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Community and Q&A

Boiler help? Over my head here…

Logan0402 | Posted in Mechanicals on

My situation: Central MA (Zone 5A), 800sq’ Cape (recent wall blown insulation), walk up attic (recent 16 inches blown insulation), unheated basement, 1 bathroom, HE washer, dishwasher, 2 adults, 1 child. Currently running on gas with a 60% efficiency (96k BTU oil boiler converted to gas).

I’ve gotten a few (too many?) quotes and everyone is offering something different. I’ve read through a bunch of threads and you guys have been super helpful, but I’m having a hard time relating everything to my own situation.

These are the four most common setups I have been proposed:

1) Lochnivar 199k combi unit (4.8gpm)
2) HTP Pioneer 100k with HTP 45g indirect
3) Laars Mascot 199k combi unit (4.8gpm)
4) Lochnivar 150k boiler with HTP Superstor 40g indirect

Combi proposals have all been 1-2k cheaper than indirect options but I worry about what I have read about their reliability and that they don’t mesh well with the slow draw of HE washers and dishwashers, apparently. However, one proposal did come with a “6yr parts and labor warranty” from the contractor, for whatever that is worth.

Right now, the one I like the best has been the HTP Pioneer. It is about 1.5k more than the average combi proposal I have received, but from how it was explained to me, it is extremely low maintenance, completely eliminates short cycling, and is just as efficient as the wall mount setups.

My biggest concern is that these all seem oversized from what I have read but fail to understand. Each contractor has been able to explain why they aren’t oversized (they modulate down), but I don’t know what to think.

I used SlantFin, hopefully correctly, and came up with a 31k heat loss reading for the house. I also attached my consumption history for gas over the last two years.

I appreciate any help deciding that you could provide.

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  1. Logan0402 | | #1

    I found another heat loss calculator on one of the threads here and did an updated, albeit rough, calculation. This one came in around 25k heat loss, I think.

    I did one for 60% efficiency and 95% efficiency to judge what I might save, if that's how it works, and it looks like about $600 a year, maybe.

  2. Josh Durston | | #2

    Slantfin will typically oversize, so your 25kbtu might be pretty close.

    What sort of emitters (radiators) do you have? Is it zoned? What sort of water temperature requirements do you have.
    I suspect your heating load is low enough that a combi is not a great fit for your house.
    Ideally you want to make sure the minimum firing rate of the boiler is less than than the load of a single zone. If running an outdoor reset (which you should) the minimum load of a zone decreases with the water temperature (if it's 15kbtu with 180F water it will be a fraction of that with 120degF water on a warmer day). It's hard to make a judgement on this without knowing what sort of emitters and zoning you have?

    Don't get hung up or fooled based on a turn down ratio like 8:1 or 10:1 or 15:1. If the boiler is dramatically oversized then even a high turn down ration won't be enough. I would be looking for a sub 10,000btu min fire rate there are some with a sub 8000 btu/hr available. A 10:1 turn down on a 200,000 btu/hr boiler will be oversized at anything above minimum fire (20,000btu/hr) most of the time.

    Generally you want the smallest boiler that meets your heating load, and with the lowest minimum modulation rate. You make up for some oversizing with thermal mass (buffer tank, high water content system, etc), but you have a chance to get it right.

    I'm not a big fan of indirects mostly due to the cost premium. A properly setup mod con with an indirect can be decently efficient. And I don't like combi's due to expensive on going maintenance depending on the hardness of the water.

    My pick would be the Lochinvar and indirect but insist on the 55kbtu model (since it's the smallest one with a 8000btu/hr min fire rate). If you're scared about DHW just get a bigger indirect but don't oversize the boiler. You don't need to size the boiler to your DHW load with an indirect, just the heating load. There is no reason to go with 150,000btu model, since its minimum fire is likely around 15,000 which is over half you heat loss making you suspect able to short cycling.

    Second pick would be the HTP Pioneer due to the thermal mass, but then you'd have two big tanks instead of one. It has a min fire rate of 35,000 but making it oversized, but the thermal mass will likely get you acceptable but not ideal run times.

    I would recommend cross posting this question on

  3. Logan0402 | | #3

    Thanks Josh! I did post on Heating Help and received a good amount of feedback. Some of it was a bit over my head and I found this website through a bunch of people talking about Dana on here.

    I currently have fin baseboard radiators all in a single zone. They are in both bedrooms, the bathroom, and the living room. The kitchen and hallway have no heat source. I am unfamiliar with what water temperature requirements are but an outdoor reset will be a part of any install which takes place as it is required to get the state rebates.

  4. Keith Gustafson | | #4

    Who is suggesting a 150k boiler to replace a 96k

    I have a 96k in a 2800 sq ft house in Mass

    They are probably oversizing, massively, for hot water which is not good idea.

    1. Tom May | | #7

      Hot water usually adds at least 40000 btu's to a system...

      1. Josh Durston | | #11

        Only if it's instantaneous. You shouldn't upsize for an indirect DHW tank. Your indirect tank probably runs less than 5% of the day which an average of something like 2000btu/hr.

        1. Tom May | | #13

          Most 40 gallon gas HW heaters are rated for around 45000 btu's. How can you say an indirect would use much less if it has to heat up the same quantity of water? The amount of btu's needed to heat a certain amount of water by x degrees is independent of what fuel or type of heating you use, the heat input is the same. If anything, you will use more since there is a heat exchange taking place between the boiler and the tank plus the added cost of running the boiler and the pump.

          1. Keith Gustafson | | #16

            Because it averages out

            first, a 100k boiler is most likely wildly oversized for the heat load

            second, the odds of needing an additional 45k of hot water at max heat load is exceedingly slim

            Your suggestions are 1950s standard and are not going to help keep heating costs down

          2. Expert Member
            Akos | | #18

            Josh is 100% correct.

            There is absolutely no need for an oversized boiler to meet DHW needs.

            A right sized boiler with a priority zoned indirect will always work, due to the thermal mass of the building, you'll never notice that the house heat shuts off during recovery.

          3. Tom May | | #23

            Keith, the only way to keep heating costs down is to turn down or turn off the thermostat. It doesn't matter how efficient a system is, it comes down to the user. No different than a car with good gas mileage, if you constantly drive 90 and brake all the time there goes your numbers.

          4. Tom May | | #24

            Akos, sure it will work, but you are robbing peter to pay paul. Hopefully you don't have to take a shower when the heat is calling and the laundry is going on a cold day. Once again, it depends on the user and their situation. A house full of teenage girls and a wife that is always cold may cause some issues. I would rather install something that will perform and follow design codes than to get call backs asking why we have no hot water or why it takes so long to heat the house and having to say I told you so.....especially for a couple hundred bucks more, the cost of adding an additional section to a small boiler.

  5. Expert Member
    Akos | | #5

    Generally a high efficiency boiler plus an indirect tank would have about the same efficiency as a good power vented hot water tank but cost much more. You are generally better off with a separate water tank, go with either a power vent unit or a heat pump water heater.

    In my area of cheap gas and expensive electricity, the operating cost of a gas and heat pump water heater are comparable.

    HTP Pioneer looks like a nice part, because it is a tank, it would eliminate the oversizing issue. A right sized HTP would certainly be cheaper though.

    Laars makes a combi heat mid efficiency unit. This is essentially a hot water tank with a coil in it for house heat. This is a single appliance and cheaper than modcon+indirect, but you really have to confirm that you can get away with 20kBTU of heat at 140F supply temp, feels a bit too close for comfort.

  6. Jeff Wasilko | | #6

    If you go with a Superstor indirect, compare the price on the Superstor Ultra. It's got a lifetime warranty as it's made from stainless steel and doesn't need an anode.

    We put a SSU-80 in a few years ago. It's built like a tank (fighting, not storage).

  7. Tom May | | #8

    Rather than go with all these fancy boilers that you are suggesting, whose companies will probably be out of business at some point and that's when it will break down and parts may no longer be available for them, why not just go with a conventional weil mclain or burnham boiler which is pretty much standard issue around here in MA. Basic, simple and efficient operation. Then consider a simple, separate gas hot water heater. A 80-100000 btu unit may suffice and cost around 1200-1500 bucks and should be an easy swap out. Another 400 for a HW tank. Plus installation of course, so something to compare to your fancy options.

    1. Josh Durston | | #10

      Cast iron is an option but still no need for more than 50kbtu (since this is likely the smallest size available), you'll still have tons of capacity for an indirect. .

      It depends on the house if a cast iron boiler would be appropriate (how it's heated and zoned). If you do go with cast iron then make sure you have proper low RWT protection to keep from rotting out the boiler prematurely (the right way to do this is to have a mechanism to decouple the house from the boiler while it comes up to temperature, different mixing valve, and pumping arrangements can accomplish this).

      Indirect DHW does not add to a heating load since it is only intermittent. Sure the tank might take 40kbtu for 8 minutes here and there, but it probably averages out to only a couple thousand BTU/hr over the course of a day (less than the typical over-sizing margin disregarding DHW).

      As mentioned by others, I would go with a standalone hot water tank either HP or high efficiency gas.

  8. Walter Ahlgrim | | #9

    In my opinion the choice of installer is more important than the equipment brand.

    A poor installer can turn the best equipment into junk and a good installer knows his equipment and how to make it work.

    I would not consider installing a unit larger than your current one, no less twice the current size.


  9. Logan0402 | | #12

    My first thought was to go with the middle ground units ~80% efficiency. The way I saw it was that the house is small, I'm on gas (cheap) already, and even at 60% efficiency I'm not paying a lot.

    However, my chimney is in POOR condition to put it mildly so a chimney vented boiler would require relining ($$). Also, MA offers a 0% interest loan which I need to use but only if the efficiency is over 90% and they also offers sizable rebates; $2400 for a combi unit and if going boiler/indirect the boiler rebates are $2000 for 90%+, $2750 for 95%+, and an additional $400 for indirect tank.

    1. Tom May | | #14

      Those rebates are good but from what i've seen, the installation costs are almost double from participating installers which kind of takes away from the rebate. Plus limiting you choice of equipment. They do this with insulation programs too. The cost I mentioned earlier is less than what the rebates are so you have to wonder how they can do it, or more so, what are they doing. Finding a good local installer whose prices are reasonable may more than compensate for the rebates. A reasonable estimate to install a small boiler and hw tank should take less than a day and hopefully not cost more than 2 grand so about 4000 + total. Around 2000+ if you can do it yourself. If you get outrageous prices over this, call someone else. Compare this to whatever systems they are pushing for the rebates.

      1. Logan0402 | | #15

        These rebates are towards boiler AND install. They also allow you to choose your own installer so long as they are licensed and insured.

        The insulation work is what they usually push their contracted workers for.

        I've had 6 proposals, cheapest for combi has been $8k (+$2750 rebate), cheapest for indirect w/ boiler has been $10k (+$3150 rebate), and the Pioneer system was $9k (+$2400 rebate) so nothing close to $4k. I've mentioned smaller systems and every contractor blows it off saying the system they are offering is fine due to DHW or modulating.

        1. Keith Gustafson | | #17

          it is exceedingly hard to find a contractor who is willing to put any thought into these issues

          I had 3 contractors who all wanted to size my system by number of feet of baseboard.

          I had to spec the actual system I wanted installed, and it happened my plumber was trained to install the Buderus that I wanted. Even they wanted to measure the baseboard for sizing, but I told them no, this is the size you will install.

          My only regret is that it is obvious I could have gone with the smaller system with no problems. I specified a 92k BTU unit and they made a 76k unit, but I didn't have the guts to go that small.

          In a house that is not overinsulated and 3 times the size of yours

          1. Tom May | | #27

            Keith, I usually ask people who call me and then proceed to tell me how to figure, design and install systems..... Why am I here? If you know what you're doing more than I do, you should be doing this yourself...then proceed to walk away. So I guess all those contractors who agreed, and all wanted to do something correctly, were all wrong...which is why they went packing.
            If you already had a "trained" plumber why did you call the other 3?

          2. Keith Gustafson | | #30


            Given your statements, contractors like you are exactly why I had to do what I did. Wildly oversizing heating equipment is not green, nor is it particularly good for the equipment. The cost of installing efficient equipment is little different from old school inefficient equipment, and the cost savings will quickly be dwarfed by fuel usage going forward. Of course that is not your problem, it is the customers problem
            Plumbers are not necessarily heating installers, and my plumber had only recently received the factory training Buderus requires to purchase their boilers. I am sure competitive bidding is a nuisance, but that is what intelligent people do to ensure they are getting the most for their money

            In 10 years the difference in efficiency has easily paid for the increased cost of the equipment, and gas equipment is much cheaper than the oil equipment I purchased, thus the cost savings, even with cheap natural gas, is quickly realized

          3. Tom May | | #31

            Most plumbers have a journeyman's license which covers plumbing, heating and gas. Your plumber installed your boiler so.....and going to a installation seminar is nothing special...a free lunch and certificate.....What I see here to often is that people do not understand that no matter which system they choose, the amount of heat or energy needed doesn't change. One poster mentioned that he would rather have a smaller boiler run longer, than have a larger boiler run less. Does that even make sense? No matter what, you are still just replacing or delivering an amount of energy. How much of that energy goes into your house, or the medium it uses, compared to the amount of energy that goes up your flue is the only efficiency factor that comes into play in the manufacturers numbers. How do YOU think the efficiency of a boiler or hot water heater is determined ? How you run and maintain it either works with or against this number.
            Real intelligent people would know how to do the install themselves, or be able find and install alternative means for free heating and cooling.
            Hopefully your new and improved, cutting edge, new space age computer controlled, wifi, phone app, alexa controlled boiler that gets 5 % more efficiency outlasts a simple stone age boiler.

          4. Expert Member
            Akos | | #32


            What you say "feels" like it should work, the problem is that there are pretty big efficiency hits for older cast iron boilers due to cycling. Take a look at figure 3 at:


            An oversized boiler costs more upfront, costs more to operate. I could see why a trade person would opt for the safer approach and oversize, call backs are bad for business.

            A modcon is more forgiving but even there one has to watch for short cycling.

            If on the other hand, one does the proper calculations (either Man J or fuel use) there is absolutely NO reason to oversize.

            From personal experience, I can tell you, replacing my 3x oversized cast iron unit with a modcon has saved about 25% on gas costs.

          5. Tom May | | #34

            Akos, once again you are bringing in more complications with modulating, condensing type boilers. They can put all the numbers they want into a spreadsheet, (those graphs were pretty funny), but as I mentioned, no matter what, you are just replacing lost btu's, so modulating up and down or trying to extract heat elsewhere, still only determines how long the boiler runs. Again, akin of going 90 and braking all the time, or off and on the gas pedal, not good. I agree with not sizing a boiler 3x as you say, but remember the topic was, should the boiler be sized up to add hot water, if so, then how much. You don't have much of a choice of exact numbers if you add a section to a boiler. Each section adds x amount of btu's so there isn't much control over whether you only need an extra 5000 or 6257 btu's... (just a funny number for those who fully believe that exact calculations matter or mean something) just gotta go with what you can get, so going from say 80 kbtu to 110 kbtu can't be changed. Add another section...140. As far as cycling, smaller boilers usually only run on demand, much larger boilers will maintain.

          6. Expert Member
            Akos | | #35

            The sad part, when I think about it, is the amount of money this attitude has wasted for many many people over the years, never mind the carbon footprint of it.

          7. Tom May | | #37

            Akos, exactly. When you think of all the man hours need to produce all these extra options, the materials and manufacturing to build these options as well as all other cost associated with all this "new" stuff does create more of a footprint as you say. Wouldn't it be better to just grab an item right off the shelf whose production has probably already paid for itself and can be produced much more easily and hate to say it but...more efficiently.

          8. Expert Member
            Akos | | #38


            Your reply just made me 5% sadder...

          9. Tom May | | #57

            Akos, perhaps you can get yourself some condensing tear ducts.

        2. Expert Member
          Akos | | #19

          An HTP UFT-80 is around $1600 on-line. If it can be side vented, depending on the old water plumbing, should be under $4k installed. There are some smaller cast iron mid efficiency unit but the cost is close, I would not go for those if your chimney is in bad shape.

          This is 95% efficient unit. It is still over sized but has a very good turndown, with a min fire of 8000btu, it should not cycle even during the shoulder season.

        3. Tom May | | #25

          Well that's exactly what I said, the rebate price will be much higher so it will average down to what a normal install would be after the rebate. If you stay away from these "deals", it may get cheaper.

    2. Craig | | #28

      Anecdotal information from my heating plant upgrades a year ago:
      Had an old 1976 150kbtu natural vent cast iron boiler and two 50kbtu water heaters. Due to mech room placement, my only option was venting out the original stack. I went with a direct vent cast iron 102kbtu boiler (87% efficiency) and a 80Gal indirect tank. 2000sf house in Alaska. With all zones running, it's -11F, and the boiler water temps are climbing; IE even my boiler is oversized for my 1976 home.

      As many have stated, oversizing of heat systems is based on instantaneous comfort demands, not system efficiency. A smaller system will almost always be more efficient running more often than a larger system running less.

  10. Logan0402 | | #20

    So would it be a good idea to reach out to these contractors again and ask for a setup as follows:

    HTP-UFT-80 boiler
    HTP-SSU-45 water heater

    Lots of these guys seemed very brand centric; married to a specific brand they are familiar with and unwilling to stray.

    1. Expert Member
      Akos | | #21

      That is a good option. I still think the indirect would be more expensive than a dedicated DHWT but they do last longer.

      Since your space heat load is so small, if you really want to get super low budget, the cheapest would be a larger power vented hot water tank with a Taco X-Pump Block to feed your space heat. The part price and install should be less but it will be around 80% efficient.

      1. Logan0402 | | #22

        Akos - at the risk of sounding ignorant, can you explain what you mean by:

        "larger power vented hot water tank with a Taco X-Pump Block to feed your space heat. The part price and install should be less but it will be around 80% efficient."

        Is this pump block just an addition to the water tank or would it make the water tank work as both DHW and a boiler? Also- what would be 80% efficient, the whole system (boiler/tank) or just the water heater?

        1. Expert Member
          Akos | | #26

          Take a look at:

          X - Pump Block (XPB), Multiple Zones - Zone Valves

          Diagram labeled "X - Pump Block (XPB)" and "Typical Installation".

          The water tank would provide heat for both speace heat and hot water, you generally want a slightly larger BTU burner. You have to do a bit of digging to find the right one, what you are looking for is something with a higher "recovery efficiency", something like (bit expensive, but you can search for cheaper):

          Recovery efficiency is the efficiency of the system when the burner is running, so this would be the efficiency of the tank when used for space heat.

          This would give you 82% efficiency for space heat and should have no issues with heating the house and keeping up with hot water demands.

          The only caveat to this setup is that it doesn't work all that well if you have hard water as the heat exchange in the X-Block will tend to scale up over time, this adds more maintenance.

          This type of setup is very cheap for DIY, I don't know what a plumber would quote it as or even if they would be willing to do it.

          You can also read more about it here:

          1. Josh Durston | | #29

            If your going this route take a look at this one:

            It may be harder to access the rebates with this configuration though.

      2. Expert Member
        Dana Dorsett | | #45

        There are limitations on what's legal to do with water heaters and "open" systems in MA. It would require a minimum duty cycle even in summer, and there's a hard limitation on the total plumbing length. It's easier to make an open system meet the legal specs with hydro-air than with baseboard.

        It's also not yet clear if the place could be fully heated with 44' of fin tube baseboard and 140F storage temps on the tank without first insulating the basement (also not subsidized in MA) or other thermal upgrades to the house. This has to be designed, not hacked.

  11. Logan0402 | | #33

    I'm also noticing a trend in these forums where the amount of radiators and desired temperatures makes a difference especially when it comes to return temps and boiler size?

    I had about 44' of fin tubed radiators and we typically have the temp set at 66 during the day and 64 at night. Occasionally we will set the temperature to 68. With a more efficient system we would probably set night temps to 64 and daytime occupied temperatures to 70.

    Does any of this information change anything?

    1. Expert Member
      Akos | | #36

      Lowering the thermostat in heating dominated climate don't change the heat load that much. When it is 10F outside, a 5F decrease in setpoint reduces the heat load by ~10%.

      Your 44' of baseboards can put out 22kBTU with 170F water. My guess is your actual heat load for the house is closer to 15k, which means the boiler only needs to provide 140F water.

      If you are running a modcon, you will get some condenstion at that temperature, the efficinecy should be around 90%. If your unit is set up with outdoor reset (which you want), during the shoulder seasons, the temperature needed would be much less, you'll get closer to 95% efficiency.

      Also check that the installer sets up the circulator properly, I've seen "professionally installed" modcons that were so over pumped that there was 5F delta between supply and return. You want the delta to be around 20F.

      1. Josh Durston | | #39

        Perhaps I missed it, but what are the water temperatures during a heating call? Supply and return?

        If you're retrofiting a modcon, there are sometimes some simple changes you can do to bring the temperature requirement down and take advantage of some increased efficiencies.

        If your up for a bit of a technical read this is a good resource: (lowering water temperature) (modcon piping)

    2. Expert Member
      Dana Dorsett | | #41

      >"I had about 44' of fin tubed radiators ..."

      At condensing temperatures sufficient to hit mid-90s efficiency, 44' of 8-10" tall fin tube baseboard puts out about 9,000 BTU/hr. With fin-tube baseboard there is very little thermal mass to work with to keep the boiler from short-cycling if it's minimum firing rate is substantially higher than that.

      At an average water temp of 170F (180F out of the boiler, 160F back) the 44' of baseboard will only emit about 22,000 BTU/hr, which is way more than an 800' cape usually needs (apparently, even before you insulated and air sealed it.)


      The BuildItSolar heat loss calculator is a very crude and inaccurate tool. With your radiation the 25K+ load calculation simply can't be right unless you're running the boiler at 200F or higher.

      Most combi boilers big enough to meet the domestic hot water requirements have a minimum firing rate close to that 22K, number, which is more than twice what the fin tube will emit at temperatures necessary to hit the published efficiency numbers. It's a ridiculous mis-match- I'd go so far as to suggest losing the phone numbers of any contractor proposing one of those:

      The minimum input of the Lochinvar NKC199N is 20,000 BTU/hr, which would be about 17,500 BTU/hr out at NON-CONDENSING temps. 20,000 BTU /44'= 455 BTU/hr per foot- it would NEED to run at ~170F to balance (even at min-fire) to keep from cycling on/off during continuous calls for heat.

      The minimum input of the Laars Mascot MFTCW199 isn't appreciably better (a rounding error) at 19,900 BTU/hr.

      The HE washers are going to short-cycle the combi-boilers- the fill cycle bursts might not even be long enough to deliver the hot water, due to the flue purge an ignition delays.

      The proposed boiler solutions are also ludicrously oversized for the design heat load, and even oversized for the radiation, at minimum modulating/condensing temps. It's absolutely senseless to install boilers so oversized for the radiation that they can't be operated in condensing mod without short-cycling, and there is NO need to go more than 50,000 BTU/hr (total) on the boiler for an indirect that is zoned priority unless you have some MAJOR continuous hot water use requirements. A 50K condensing boiler puts heat into the indirect faster than a typical 50 gallon standalone, and the recovery times are short- short enough that it releases the boiler for space heating service by the time you're dried off and dressed after a shower.

      This has all been covered before:

      If the basement walls aren't air sealed and insulated the foundation losses are going to be a significant fraction of the total fuel use now that you've insulated the rest. A SINGLE square foot of uninsulated above grade poured concrete foundation wall loses as much heat as 10 square feet of insulated 2x6 framed wall, or 7 square feet of insulated 2x4 framed wall. So even if the "unheated" basement is allowed to drop to 50F, the heat loss is still quite substantial when it's averaging 25-30F outside. Insulating the foundation walls to the current IRC code-min R15 continuous insulation is "worth it", and reasonably cheap & green if doing it with reclaimed roofing foam.

  12. Matt V | | #40

    The performance of indirect DHW systems in the summer is not very impressive, based on this study:

    I think #11 is most representative of a condensing boiler with indirect DHW tank. To me it would be hard to justify the extra cost compared to a standalone water heater, but if you have no good way to do atmospheric venting then indirect might be worth it.

    A couple other papers that might be helpful:

    1. Expert Member
      Dana Dorsett | | #42

      >"I think #11 is most representative of a condensing boiler with indirect DHW tank."

      Look at Appendix 11- that's a LUDICROUSLY oversized 160,000 BTU/hr mod-con, probably with no more than a 5:1 turn down ratio. Even so it would still beat most standalone tank water heaters, but probably not a condensing tank water heater. A more appropriately sized 40-50K mod-con with a turn down ratio of 5:1 or greater would do better. There are several 80-85K mod-cons with 10: 1 turn down ratios that would be OK here too.

      If all else were equal a 1.5-2 ton ducted cold climate mini-split and a heat pump water heater in the basement (to keep humidity down) would be a better overall solution to the heat & hot water (and AC!) needs of a tight 800' cape with 1 bath and HE appliances. But I don't believe there's any subsidy money for going that route (yet).

      1. Matt V | | #43

        It's not the best study. They look at mostly old outdated equipment, rather than what we should install going forward. I agree an indirect water heater would be more efficient than a non condensing tank, but my point is when you consider the efficiency over the whole year it's not as much better as you think, and it might not be enough to justify the cost. Hot water might consume a few dollars of gas per month (maybe $5-15 for a small to average household?), and a slight increase in efficiency on a a small amount might never justify the large upfront cost.

        A Sanden CO2 split heat pump water heater would probably be great for this house (and mine), if they weren't so expensive. One of those combined with a small mini split would be enough for heat and hot water.

        Where I am, the fee for having gas service is around $16 a month even if I use no gas. Eliminating that is another small benefit of going all electric.

        1. Expert Member
          Dana Dorsett | | #44

          >"It's not the best study. They look at mostly old outdated equipment, rather than what we should install going forward. "

          It actually IS the best study that's readily available, and was instrumental in getting cast iron boiler manufacturers to include heat purging economizer controls as standard equipment.

          But it IS a bit dated, and it doesn't really delve into what it would be if the mod-con boiler was reasonably right-sized for the heat load of an 800' house, which I would hazard to be no more than 15-17,000 BTU/hr @ 0F (or whatever Logan0402's local design temp is.) That mod-con is something like 10x oversized for the space heating load of this house and they only compared it at 2x and 3x oversize factors in Table 3 (page 9).

          The duty cycle in water heating only mod of a 50K mod-con (still 3x oversized for the space heating load) would be 3x higher than the monsterousity tested in system 11. Also note, the steady-state efficiency of that oversized boiler was 88.5%. Most current mod-cons are in the mid-90s for steady state efficiency. The higher duty cycle in water-heating-only and higher steady state efficiency would move up the summertime efficiency numbers to where it should beat any non-condensing tankless, and would be pretty similar to a condensing tank.

          If they're chasing subsidy money they can't get it out of MassSave with a roll-your-own tank-type combi. HTP won't support using the Phoenix series water heaters with baseboard systems, only hydro-air, and only "open" systems. While reasonable hydronic designers can make it work reliably and well with other types of systems, the manufacturer's lack of support and the state's lack of subsidy makes that approach less viable.

          The only wall hung combi-boiler I can think of that might make any sort of sense here given that it's a 1-bathroom house is Navien's NCB-150. It has enough burner to handle a single full flow shower with some margin (but not a lot), and it modulates down to 12,000 BTU/hr-in, or 11,000-11,500 BTU/hr out. 11,500/44'= 261 BTU/hr per foot, so at an output temp of 130F-135F it will balance perfectly with the heat emittance of the baseboards with 90-92% efficiency, and dropping it to 120-125F out it might still be tweakable to not short-cycle.

 (click the "specifications" tab.)

          The max 120KBTU-in on the hot water side translates to about 110,000 BTU/hr-out. When the incoming water is 35F (it happens in some central MA locations) and the shower output is 105F, a 70F rise, that limits the total flow rate to 110,000/70F = 1571 lbs/hr, or (/60=) 26.2lbs/minute, or (/8.34=) 3 gpm. So with a low-flow <2 gpm shower it can still work with a hint of margin, but wintertime tub fills would be a bit tedious. With a drainwater heat recovery heat exchanger (probably not subsidized) a lot of margin could be built into the showering performance though. The EcoDrain VT1000-4-54 (4" drain x 54" tall) delivers more than half of the heat of a shower back into the incoming stream, freeing up another 1-1.5 gpm of burner capacity for other uses.

          >"A Sanden CO2 split heat pump water heater would probably be great for this house (and mine), if they weren't so expensive. "

          It's probably not enough to cover both the hot water and space heating needs of an 800'' cape house in central MA, and would need to use anti-freeze- it does occasionally hit negative digits here when the power grid is down.

          Cold climate mini-splits and a heat pump water heater fully inside an insulated basement makes sense. Most homes in central MA need mechanical dehumidification to keep the basements from stinking- better to put the heat-of-vaporization recovered into water inside an insulated tank than putting it toward heating the basement.

          1. Logan0402 | | #46

            Dana and Matt - that's a lot of good information and it looks like I'll have to read it all again after work tonight to understand it.

            I can provide the following insight:

            -My current boiler goes into a high heat hold at 119 degrees, I think.

            -The basement is cement block and the only insulation is in the joists below. It does get cold in the winter (not sure exact temp) and very moist but not wet in the summer.

            - I believe my design day temp is indeed 0 degrees. I live in North of Worcester MA approx 5 miles from the NH border.

            Do you have any tips on finding a contractor that will listen regarding a smaller system. I've had 6 quotes done and no one seemed to want to hear about going smaller since they all wanted to go combi and if we do that I won't settle for less than 4gpm, maybe 3.5gpm.

            The only contractor who seemed interested in talking is the one who wanted to put the HTP Pioneer 100btu high-class boiler in. He acknowledged it was oversized but said due to it's high mass that it would alleviate the short cycling. I liked him a lot, so I hope there was some truth to this.

  13. Expert Member
    Dana Dorsett | | #47

    >"The only contractor who seemed interested in talking is the one who wanted to put the HTP Pioneer 100btu high-class boiler in. He acknowledged it was oversized but said due to it's high mass that it would alleviate the short cycling. "

    The Pioneer/Versa Flame series combis are basically a pre-engineered modulating verision of what might be built around a tank type condensing water heater. It's WAY overkill for your loads, but he's telling you straight- it won't short cycle due to the thermal mass and control features that make best use of it. But it would NOT need a 42 gallon indirect- even the 55 gallons of storage capacity is overkill , unless you have a huge soaker-tub to fill in that one bathroom. It's probably the most expensive of any of the proposals. (Can you ballpark the quotes for us?)

    With the boiler/water heater in the basement you'll still want to air-seal and insulate those CMU walls. Air sealing basement ceilings adequately is nearly impossible- walls are much easier. There are multiple vendors of used and factory seconds foam board operating in Worcester county that can even make it pretty cheap. (I used to have the card of a small operator in Winchendon, but can't seem to find it.) The biggest is Green Insulation Group in Worcester.

    1. Logan0402 | | #48

      From what I understand, the Pioneer is a high thermal mass boiler that does not produce DHW on it's own, thus the addition of the indirect. The Versa Flame I was unaware of, but it looks like they make a 130btu, low fire at 35kbtu, and that is a combi unit. He only quoted for the Pioneer and did not mention the Versa. I will say that he made it clear that 95% of their installs are the Pioneer.

      Basement insulation has been a thought but the moisture in the summer gave me pause. I can't afford to both seal the moisture out and insulate, to be honest. I added a dehumidifier but my electric bill skyrocketed almost $75 per month. Would worry that adding the rigid foam alone would trap moisture; would that be incorrect?

      As far as the quotes go:
      Q1) HTP Pioneer 100BTU w/ 45g Indirect: $9,000 to include removal of old boiler plus the addition of a 5ft fin tubed radiator installed in kitchen (currently unheated) *He originally came in at $10,000 but when I balked at the price he came down to this price within half a second.

      Q2) Lochnivar 199btu combi unit: $8250 w/ 5ft fin tubed radiator installed in kitchen (1yr warranty) :OR: Locnivar 110btu w/ PowerStor 40g: $10,400 w/o removal of old boiler

      Q3) Laars Mascot 199btu combi: $8,000 w/o any additional radiator install and leaving old boiler in basement (6yr part/labor warranty)

      Q4) Lochnivar 150btu combi: $8,000 +$500 if installing 5ft fin tubed radiator :OR: Lochnivar 110btu w/ 45g PowerStor: $10,000 +$500 if installing 5ft fin tubed radiator.

      Q5 & Q6 were both for Lochnivar 150btu w/ indirect, $11,000/ea

      1. Expert Member
        Akos | | #49

        Because the Pioneer has the tank built in, you don't need an additional water volume to meet demand, you still need some extra plumbing since you can't mix heating and potable water:

        It does save some money over an indirect, but it is not a standard setup that most heating guys would be familiar with. They will probably quote more for this setup than an indirect.

        1. Logan0402 | | #50

          From my understanding the Pioneer cannot provide DHW on it's own, and requires a water heater. The Versa Flame is the "sister" to the Pioneer that acts as a combi unit.

          1. Expert Member
            Akos | | #53

            The Pioneer CAN provide DHW with a correctly sized plate heat exchanger as in the link I sent. With the right sized plate HX, the 55 gallon tank backed by a 100k burner, it can easy supply hot water to 2 bathrooms.

            The Versa is nice, but way too expensive. A UFT + Indirect is way less money.

          2. Expert Member
            Dana Dorsett | | #55

            That's right- figured it out when looking at the Pioneer-only manual:


            It is essentially a water heater without the heat exchanger for isolating the potable, ergo the need for the indirect. The Versa Flame (and no indirect) would most likely be a better solution for your loads but probably even more expensive.

            An indirect makes for a pretty expensive "heat exchanger" compared to Akos' recommended plate heat exchanger solution, but the latter requires design competence on the part of the installer (and a knowledgable code inspector), and it may not qualify for rebate subsidies if configured that way.

            A UFT-080W + indirect should come in under $9K if put out to competitive bid, maybe even under $8K. That boiler modulated down to ~7600BTU/hr out (x 44' = 173 BTU/hr per foot), so it should be able to run at 120F- 125F-out without short cycling.

        2. Logan0402 | | #52

          I just tested the tub in the bathroom and it flows at approximately 3.5gpm. That, as it stands, is about as low as I would want to go because it already takes a while to fill the tub. The shower head is approximately 1.75gpm.

      2. Josh Durston | | #51

        Quote 4, but with a 50kbtu Lochinvar to get the 8000btu min fire rate.
        (80kbtu is almost the same but completely unnecessary).

        I agree with Dana's sentiments that it's hard to trust a contractor that is pushing such over-sized systems. I'd be concerned about other design designs they may make (regarding pumping and such).

        I'd reach out to your short list and ask for some references and photos of jobs. Also get specifics on supporting components such as piping, hydraulic separation, pumping, air elimination, control strategy, water quality management (PH, TDS), etc.

        1. Logan0402 | | #54

          Are you referencing asking Quote 4 to re-quote the indirect option? So the 50kbtu Lochnivar wall hung boiler with the 45g indirect? Probably won't save money on the quote, but I see how it would be more fitting.

          1. Expert Member
            Dana Dorsett | | #56

            There are a couple of smaller Lochinvars that would be appropropriate- the WHB/KHB-085 modulates down to 8500 BTU/hr-in which isn't much higher than the WHB/KHB-055's 8300 BTU/hr-in. Either would be quite a bit less expensive than anything in the 150K range, and would not short-cycle on a 44' zone of fin-tube at condensing temps. The -085 would have noticeably faster recovery on the indirect, not that you'd necessarily need it.



            The Knight series boilers have lots of setup bells & whistles options that you'll never need. Cheaper still would be the Lochinvar NKB080, which is a somewhat simpler boiler than the WHB/KHB-085 , which also modulates down to 8300 BTU/hr in:


            That boiler is comparatively simple to set up almost as simple as the UFT-80W that it's most similar to. But the UFT series boilers are pre-plumbed with a separate port w/control for the indirect, making it simpler to install. If Lochinvar, the NKB080 is probably your best value, but it's still about a grand more than HTP's UFT-080 or (Westinghouse labeled WBRUNG080- same boiler) at internet pricing.

            The NKB150 + indirect would be better for hot water delivery than the NKC150 combi they quoted, but the min-fire input is 15K for ~14,250 BTU/hr-out at 95% efficiency. That's (14,250/44'=) 324 BTU/hr per running foot. That puts it into short-cycling territory unless the output temp is north of 135F, which means it won't be condensing (much), and at your likely heat load modulating-never.

  14. Expert Member
    Dana Dorsett | | #58

    >"Again, akin of going 90 and braking all the time, or off and on the gas pedal, not good. I agree with not sizing a boiler 3x as you say, but remember the topic was, should the boiler be sized up to add hot water, if so, then how much."

    If the water heater is zoned priority, with one bathroom and no big tubs to fill there is no need to up-size the boiler, even with a tiny cast-iron boiler.

    A non-modulating boiler that's oversized for the radiation has no choice but to go 100(%) and jam on the brakes. In this case we're dealing with 44 feet of baseboard, which even at 200F EWT isn't going to emit as much as 30,000 BTU/hr.

    The available selection of non-modulating boilers that can run even at 80% as-used AFUE on that little radiation is pretty limited. The only one that comes to mind is the Burnham 202, which could easily handle both the hot water (zoned priority) and likely heat load of that house and would probably hit pretty near it's 82.3% AFUE.

    The steady state output of that boiler is about the same as most standalone 50 gallon water heaters, and for a 1-bathroom 3 person house there would be no point to up-sizing either the boiler or the indirect. The DOE output is getting on to 2x the actual heat load of that house- the indirect would give it a higher duty cycle, improving net efficiency.

    Based on the most recent December bill in the attachment assuming 80% efficiency (which is probably generous) and zero hot water use (not likely) the heat load of this place is less than 17,000 BTU/hr. Assuming 3x oversizing factor with more idling losses and daily bathing it's probably close to or even under 15,000 BTU/hr

    The fact that the boiler would be in a basement with no wall insulation and an insulated ceiling above, the standby losses of that boiler would be pretty much true losses, those lost BTUs won't be offsetting the heat load. Depending on the size and condition of the flue venting the old boiler it would most likely need a narrowing flue liner, but since it's such a low combustion efficiency it needn't be stainless.

    The street price of the Burnham 202 boiler through MA distributors costs about $100 MORE than the HTP UFT-080W, and there is more labor and design work to make it work with an indirect than the UFT. The overall installation would come in CHEAPER, with the value-priced stainless UFT mod-con than the cast iron Burnham 202.

    And there's subsidy money to offset the installed cost of a UFT, none for a Burnham Series 2. So what would the rationale be for going that route?

  15. Logan0402 | | #59

    I have a few more contractors coming by this week and I plan to use all the information you guys provided to push for a correctly sized system. I really appreciate the time you all took to provide insight.

    I attached a very rough outline of the house and how the fin tubed radiators are set up. It looks like the heat output splits and one line goes to the living room and the other goes to bedroom 1, bedroom 2, and then the bathroom. Both lines then meet back at the boiler. Does this seem right or should they all be on the same loop? Is the house too small to have 1 zone for the kitchen/living room and 1 zone for the two bedrooms and bathroom?

    1. Expert Member
      Akos | | #60

      Because your loads are so low, the best way to zone your setup is if you go with a tanked boiler. I doubt that is worth the additional cost.

      You can also get there with a standard modcon+indirect with the indirect as a parallel zone without a zone valve. This would let you use the mass of the indirect to keep your boiler from short cycling while only heating one zone. When any zone is calling for heat, you would also be flowing water through the indirect. When there indirect needs to re-charge, you just turn on the circulator without any of the zone valves open with water only flowing through the indirect.

      This would mean your modcon output temperature would have to be pretty high, which is not the most efficient way to run it.

      Also it is not a "standard" setup. You would need a knowledgeable plumber to set it up so it works properly.

      I run something close to this at home. It works pretty well especially if you have a larger indirect tank.

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