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Community and Q&A

Adding a Heat Pump and Other Energy Upgrades

johnstith | Posted in Mechanicals on

We bought our house last Monday! We know it pretty well because we’ve been renting it for six years.


Our old gas boiler stopped working on Friday! Now we are true homeowners – it’s 15F outside and we’re living on space heaters.. 🙂


I had visions of carefully planning out a green retrofit. If the gas boiler can’t be fixed, we will have to greatly accelerate that.


Seems like yinz enjoy a puzzle, so here’s mine – all advice welcome!


Our house was built in 1947 on a concrete slab, with a footprint of about 1000 square feet plus an improved attic. We will add insulation where possible this year, but with the improved-attic ceiling in place and some questionable roof ventilation, we may have insulation limitations for many years. The south roof is partially shaded by neighbors’ trees, so I am dubious about adding solar panels. Small detached shed, no garage, and we’re perched at the top of a little ridge, so no place to drill geothermal. We’re in the Maryland suburbs of DC (IECC Climate Zone 4).


Our malfunctioning ancient gas boiler is in a tiny utility closet in the center of the house. The boiler feeds hydronic floor heat plus a hydronic air handler that sends air heat through ducts. Our aging central-air condenser uses the air handler and ducts as well. We enjoy the warm floors but we also like the air heat so we can have a cooler house for sleeping, then a quick burst of heat when we wake up.


That tiny utility closet also has an ancient gas hot water heater. Our hot-water use is average – one shower but several users.


I’ve read the debates about various ways to help the environment, and our choice is to phase out all fossil fuel use, if at all possible. We are willing to pay more for electric. The only way we’d buy a new gas unit is if we can’t find a local contractor to install and maintain the needed electric unit. Circuit box says 200 amps – we seem to have plenty of room for more electric use.


I’ve been told any new gas equipment in our tiny utility closet would require re-doing the ventilation because what we currently have is not up to code. With any type of new units, we may need small options to fit the closet.


We would like to keep the radiant floor heat, but if it’s likely we could insulate the slab and floors sufficiently for the floors to be room-temperature, instead of cold, we would consider abandoning the radiant heat.


We may need to break up the work into phases to spread out costs. And if our gas boiler can’t be fixed, we may need to address heating first and quickly.


So for air heat, would you use a heat pump with our current ducts? Or use a mini-split and close up the ductwork? It would be great to get rid of the huge air handler in our attic eaves, as we could really use more storage space. Any other green options?


For the radiant floors, I’m dubious about maintaining a solar thermal system – will it be worth the expense and maintenance? We could get an electric-resistance boiler, but the electricity will be expensive for what we get. How well would floor insulation work – should we just abandon the radiant floor system? What would you do?


For hot water, a heat-pump water heater would have to be inside our heating envelope, though maybe we could duct it up the chimney currently used for the gas units? And we would have one with electric-resistance backup – would that cover us on cold days? Would that complex heat-pump water heater design still be better than a simple electric-resistance heater? Any other options?


And finally, how do I find the local contractors who will do these green retrofits on a moderate budget? Should I hire a consultant first? I see energy auditor online, but few claim to advise on major HVAC issues. And when I look at the local HVAC companies, they do mini splits, but no one mentions installing electric boilers or anything unusual. I’m enjoying the many innovative ideas written up on, but how do I actually get something unusual installed?



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  1. charlie_sullivan | | #1

    If your slab has no insulation under it, heating it is not a good option--lots of the heat goes in the ground. Insulating above the slab--foam and a new sub-floor above the foam--can work well, but you lose headroom. So the question is how much headroom you have and how much are you willing to lose?

    No need to duct a heat-pump water heater to the outdoors. It will still be much better than an electric water heater, even in the winter.

  2. paul_wiedefeld | | #2

    If the boiler can be fixed, you have time to explore air-to-water, otherwise air-to-air using the existing ductwork will be the easiest and most effective path here. Luckily, you’ll have plenty of contractors familiar with that. Heat pump water heaters are the weakest link in the electrification process in my opinion: many are loud, unreliable and expensive and cool off spaces you might not want cooling in. A long lasting resistance heater might be worth considering, it’ll be more expensive to operate but more reliable and silent.

  3. creativedestruction | | #3

    Sounds like your best first investment may be a central air source heat pump that utilizes existing ductwork. That will get you efficient electric heating and cooling and there should be plenty of contractors that can handle that especially if you're open minded on what brands they can get good pricing on. Compare specs and proposals once you have a few bids. Your current energy bills should help with system sizing.

    Next investment--heat pump water heater. No longer niche. Available at the big box stores.

    Then put some thought into the floor heat/slab insulation conundrum.

  4. johnstith | | #4

    Thanks everyone -- keep it coming! On the first few questions: I'm assuming the slab does not have insulation underneath or along the sides, given the house was built in 1947, but I don't know for sure. When we leave the radiant heat off for several days, the floors get quite cold.

    Our current headroom is 8'3". So we could lose a bit. We have a small fireplace with a little tile flooring in front of it -- that would be a strangely sunken fireplace if we raised the floors with insulation, but our house is not exactly a museum, so what the heck.

    1. paul_wiedefeld | | #5

      Do you know if the radiant floor is original? I didn’t know they did in-floor heating in the 40s.

      1. johnstith | | #6

        Indeed they did -- I just found this article about radiant heat in Levittown! And sure enough, the snow sticks last closest to our house. Hmmm.

      2. user-6623302 | | #10

        All of Levittown, NY is copper in concrete radiant heat and built in that era. No insulation, just gravel.

      3. paulmagnuscalabro | | #18

        Not to veer too off-topic, but I think Frank Lloyd Wright was using radiant floor as early as the 20s? He definitely incorporated it in a lot of his Usonian houses, I think using copper pipe in the slab.

  5. Expert Member
    BILL WICHERS | | #7

    I would absolutely explore repairing the existing boiler first, which, if possible, buys you time to make a better decision about your future plans. Rushing into anything is not conducive to getting an optimal result! :-)

    If your goal is reduced energy/fuel use DO NOT consider electric resistance heat. Electric resistance in most areas will use more fossile fuels than using natural gas directly. The reason for this is that most new electric generation over the past decade or two has been with natural gas fired turbines. Due to ineffiencies and losses in the system, using electricity generated from natural gas for heating will actually consume more natural gas than burning it directly for heat.

    With heat pumps, it's different -- because heat pumps MOVE heat, they don't MAKE heat, so they allow you get more output BTUs than input energy. That's a great way to go for energy efficiency, but it means switching over to heat pumps. I'm not aware of any heat pump boilers that would be able to keep your radiant system functional though.

    If you're able to repair the boiler, I'd do that for now and operate normally while you research your options. If you go with minisplits or some other type of heat pump system, keep the boiler as a backup for extremely cold days, or just in case of a failure with the heat pumps. Make sure to run the boiler periodically if you do this, just to keep the system from sitting and rotting.


    1. charlie_sullivan | | #15

      Enertech Advantage air-to-water would be likely to be capable of the job, but that doesn't make it a good idea to keep heating the ground, and given the 8'3" head room insulating the floor on top of the slab sounds viable. Maybe 1.5" of GPS.

      Enertech Advantage flyer with basic specs:

      Excellent advice to buy some time to make a good decision if possible.

  6. Expert Member
    NICK KEENAN | | #8

    If the boiler hasn't rusted through and all the water is on the floor, it probably can be fixed. Does it have a pilot light? It's probably the thermocouple, some people replace that as part of annual maintenance. It may also have electric ignition, the ignitor is a simple replacement. I'm trying to think of what else can go wrong -- the circulator, the aquastat -- those are couple hundred buck fixes.

    The real day of reckoning is the day you go down there and there's a puddle of water under your boiler expanding through the basement.

    1. johnstith | | #11

      We had a tech in on Friday -- I think he checked the easier things. He's coming back on Monday with the tool to do a conbustion analysis. He is concerned about the heat exchanger and the flue, if I understood correctly. He found that a "rollout safety" tripped, if I understood correctly, and he doesn't know the root cause of that. He said if our chimney is blocked (which is possible -- it's not capped), that could cause this. We are keeping it off this weekend out of an abundance of caution around carbon monoxide. (We do have the typical home CO detector.)

      So no puddle of water, and I'm happy to hear your optimism and others' that other things should all be fixable once diagnosed!

      1. Expert Member
        NICK KEENAN | | #13

        The rollout switch has a reset button. With the chronology you've laid out I'd be highly suspicious that this has been an intermittent problem and the previous owner was just hitting the reset button when it happened.

        The rollout switch trips when the combustion isn't going up the chimney. Usually this is caused by a blockage. If it's intermittent I'm wondering if you've got a situation where when the wind is just right or something it blows back down the chimney. It was quite windy all up the east coast this weekend.

        If it is intermittent the tech probably won't find it unless you get lucky and the conditions happen to occur while he's there. It may be that giving the chimney a good cleaning helps. Or replacing the switch may make it less sensitive.

        1. Expert Member
          NICK KEENAN | | #14

          Although I'll add that gas burns clean and doesn't tend to clog chimneys. Usually if your chimney is clogged it's because something built a nest during the summer when the burner was off.

          1. johnstith | | #16

            Maybe! It has been windy some days. The gas hot water heater vents to the same chimney, so there's a bit of venting all year.

            We've lived here several years (previously as renters) and no reset button was never used on the boiler. (We got a fair price in our purchase -- the house has many issues!) Last Monday I noticed the boiler was humming without firing for about ten minutes in the morning, even though the thermostat was calling, but then it did fire. Happened again the next morning. Then Friday morning, it happened for an hour, which is when I turned the thermostat off and had the repair technician come out.

            This has been the coldest month in Maryland in several years, so I was expecting him to say the system was overloaded and needed a break, or something like that. (I don't know much about gas boilers!) When he said some switch had turned it off, that was surprising, because it didn't seem to match the intermittent problem I was seeing.

            Thanks for the suggestion of replacing the switch -- I may bring that up if the tech doesn't come up with a plan.

          2. Expert Member
            NICK KEENAN | | #17

            Humming without firing may not mean anything, unless it's a new noise you've never heard before. Typically the thermostat is connected to a pump called the circulator that pumps water through the system. The boiler has its own thermostat called an aquastat that turns the burner on when the water temperature gets below 160F and turns it off at 180F. The boiler might hold ten gallons of water so the burner only fires occasionally.

            So if the thermostat is calling for heat, but the water is still above 160F, the circulator runs but the burner doesn't fire. Or if the boiler is below the set point but can't fire for some reason the circulator will still be running. The circulator makes a humming noise and absent other information I would guess that's what you're hearing.

  7. walta100 | | #9

    Let’s not jump on the worst cast conclusion so fast.

    Unless water is leaking out of the boiler it can almost certainly be repaired for only a few hundred dollars.

    Making the repairs will give you the time you need to upgrade your air sealing, insulation and collect fuel usage data with your new insulation needed to size the new heat pump you want.

    Is the current air handler & duct work in the attic? If so I think the smart move would be to abandon them and plan new ducts inside the conditioned space or a ductless plan.


    1. johnstith | | #12

      Great to hear the optimism about boiler repair. And yeah, I'm realizing anything an HVAC contractor proposes this week will be oversized because we haven't done the insulation project yet!

      Yes, the air handler and lots of big flexible duct tubes are within the attic eaves, which are inside the insulation envelope (to the extent we have an insulation envelope), because the majority of the attic is an improved bedroom.

  8. GBA Editor
    Kiley Jacques | | #19

    Check out this new series on planning for a furnace to heat pump retrofit by Jon Harrod—it’s right up your alley: Planning a Furnace-to-Ducted Heat Pump Retrofit, Part 1 and Planning a Furnace-to-Ducted Heat-Pump Retrofit, Part 2: Data Collection. Part 3 will be published this Wednesday and is about sizing.

    1. johnstith | | #20

      Thanks Kiley, I'm checking that out! Installing a heat pump in our home appears to be even more straightforward, because we already have a traditional (horizontal) air handler in our improved attic for our current central-air / hydronic-fan-coil-for-heat-system. We'll probably get a new air handler, but the space and ductwork is all set up for it.

  9. johnstith | | #21

    Update on our situation: Our gas boiler has huge amount of buildup on the heat exchanger, blocking its effectiveness (and leading to way-high carbon monoxide levels inside the unit). The buildup apparently occurred because the chimney has not been capped (not for at least the six years of us renting the house), so plenty of rainwater has been flowing down into the boiler. Repairing the heat exchanger would require taking the boiler outside, a huge job we will not be having done. So the gas boiler is dead!

    I've broken our project into four phases -- what do you think?

    #1 Replace central air and hydronic-heat fan coil with a new split air-to-air heat pump, using existing ducts. This is the only sure way to get heat-pump efficiency for the ducted heat, due to possible limitations on air-to-water solutions in our house (described below). It's also a typical solution that can be installed quickly. (We're currently running five space heaters!)

    #2 Insulate insulate insulate.

    #3 Pick a new water heater -- hopefully heat-pump, but it could get quite expensive to add ducts to this tight house or install a split system. Our utility closet is literally 100 cubic feet and doesn't seem to have any potential duct routes to the too-warm improved attic. Putting a heat-pump water heater in the improved attic would be in-the-way and add a lot of new plumbing. Also if it's worth the electric use to not have cold floors, either use the radiant floor heat (perhaps an indirect tank off the water heater), or perhaps re-do the floors with insulation and/or electric floor-heat matting (which also seems expensive given all the changes to doors and stairs a higher floor might require).

    #4 Install a small woodstove in our old small fireplace, or perhaps home battery storage, as a heat backup for power outages.

    #5 Finish electrification with new stove and clothes dryer, and shut off the gas.

    I have three contractors visiting today and tomorrow. If we end up with an oversized heat pump because we don't know how successful phase 2 (insulation) will be, will that cost a lot more in electricity long-term? Or is it just that I've needlessly spent a few hundred more on the system itself?

    My hope is they think phase 1 (heat pump) doesn't depend much on whether we keep heating the floors (phase 3) or not. The same question arises -- if we buy a heat pump now that turns out to be oversized, is that an efficiency drain, or just an upfront needless cost?

    Thought you'd enjoy the attached photo of our poorly uninsulated home in winter. Warmer ground along the edge (snow melts first) due to an uninsulated slab. Warmer roof above the overhangs, due to poorly insulated ceilings. Much to do!

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