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Community and Q&A

So Confused: HRV, ERV, Dehumidifier, Ductwork

josephny | Posted in General Questions on

I’m gut renovating a 100 year old, 4500 sq-ft, 3 story home (plus unfinished, but in-the-envelope basement).

I’ll most likely be spray foaming and have a pretty tight house.

I’m trying to figure out the HVAC and ventilation plan.  I really like radiant heating, but that doesn’t solve the ventilation or AC needs.

I’ve been reading about ventilation needs, ERVs and HRVs, positive and negative pressure, etc.

House is in Sullivan County, NY, where the Winters are zero degrees (F) and the Summers are 100 degrees and the humidity has a range almost as large.

House is 34×45 with 11′ ceilings on 1st floor, 10′ on second floor and 3rd floor is dormer/attic style with average ceiling height of ~7′ (roof slopes down to touch exterior walls and peaks at 14′).  Basement average ceiling height is just under 7′.

Should I use radiant heat?  Should I go with a ducted HVAC?  Mini-Split?  Separate AC?  Integrated ERV/HRV?

Sure would appreciate some advice.

Thank you!

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Replies

  1. billfrombirchwood | | #1

    We remodeled our 2 story 2000 ft and replaced our subfloor with warmboard which is radiant floor heat. The pex manifolds for the warmboard connect via a heat exchanger to our DHW tank. The tank is currently heated with a ng boiler but could be swapped out with an air to water heat pump. For ac, we currently have ductwork and a air handler that circulates air. In 2020 hindsight, I should have installed a heat pump and a hydronic air handler for cooling and dehumidification. Since the duct work just handles ventilation, you can use ERV/HRV that plug it into the return and supply.

    1. josephny | | #3

      Very interesting. Do I understand correctly that the NG boiler produces the heating for the warmboard as well as the hot water through a DHW heat exchanger type? And completely separate from that for cooling you use an air handler and ductwork? What produces the cold air?

      Thanks!

      1. billfrombirchwood | | #6

        Here is an example configuration for Climate Zone 6. The Heat Pump produces hot water and cold water. The Hot water goes into a Large Tank and the Cold water goes into a buffer tank. The hot water pre-heats the water which then goes into a booster to bring the water up to 107F. Instead of electric backup heat - you can use Natural Gas boiler as backup heat - with some additional piping. Today, NG is still cheaper, once solar gets lower in cost then Electric will be cheaper.

        Dehumidification and Cooling (Cold Air) is produced by running the Air Handler over a chiller water. The chilled water picks up the heat from the air and transfer the heat to the outside via the Heat-Pump.

        Since the air handler is only doing ventilation (not forced air for heat), you can add an ERV/HRV to the ductwork and still have a balanced system. Broan (Venmar) make some good units.

  2. charlie_sullivan | | #2

    I'd recommend ERV for a large house in a cold climate, unless you have a lot of people living there. The rate of people producing moisture inside will be low compared to the volume, so you'll want to retain that moisture to retain comfortable humidity in the dead of winter, and it will help you maintain low humidity in the summer, in conjunction with A/C and perhaps active dehumidification for the shoulder seasons.

    I'm not sure what drove your decision to use spray foam, but you can probably do better in all respects with something else, whether you prioritize high R-value, good value for the money, excellent air tightness, or minimal overall environmental impact, you can do better on any of them (or all of them) with a different approach.

    If you want to use hydronic heat, either with panel radiators or radiant floors, a good, modern, climate friendly way to do that is with a heat pump, either an air source heat pump that has an outdoor compressor pulling heat out of the air, or a ground-source heat pump that pulls heat from underground tubing in a well. You would be looking for a "water-to-water" ground-source heat pump. You can then do cooling either with ductwork and a few "fan coil" units where the air is blow across coils of cold water from the heat pump, or you can use ductless slim fan coil units that mount on the wall in each room you want to supply with cooling, with the chilled water piped to them. All of that stuff is pretty specialized work and you'll need to work hard to find someone qualified to do it.

    1. josephny | | #4

      I've been reading that ERVs could have problems like allowing pollutants in.

      The average daily number of people will be low across any 12 month period (it will be used only occasionally), but there might be a handful of 2-3 week periods with 20 people in the house.

      i havent' sprayed yet, and would be happy to find an alternative, but I need r-49 on the roof and r-25 for the walls and I can't figure out how to achieve that without substantial furring of supports to create far more depth for other types of insulation. And, being ignorant of the dynamics involved, I am worried about getting the vapor barrier issue correctly handled. From my limited understanding, with closed cell foam, I don't have to worry about it -- outside stays outside and my surfaces won't be suspectible to dew point condensation.

      I am also not decided on hydronic heating.

      What I'd really like is a heating/cooling/ventilation/humidification-control system that doesn't cost a fortune, is completely silent, has no possibility of accumulating dust/dirt, is super reliable and energy efficient. Should be easy, no (;-)?

      Thanks!

      1. charlie_sullivan | | #5

        If your occupancy is large numbers of people for short times, that might change some of the calculus--you might want an HRV on super low plus a temperature setback when it unoccupied, and then run it much higher when there's a crowd. But if you have ERV for normal use and the humidity gets too high with a crowd, you could open some windows.

        ERV could potentially transfer some pollutants from the outgoing airstream back to the incoming. But only very small molecules, so it's not many, and not all transfers, so you are still diluting it. If your hobbies include a lot of solvents, you might want to choose HRV or do more research, but in general, I wouldn't worry about it.

        Yup, the insulation thickness will need to be more with other kinds of insulation. And you need to make sure you have the air sealing and vapor control done right. The good news is that when you do that, you have also addressed the thermal bridging through the studs/rafters. Putting high R-per-inch insulation between rafters means that the heat will mostly leak through the wood, and you won't really get the R-value you paid for. Same with the walls. The R-49 between the rafters will meet code, but it won't give you the whole system R-value of R-49 cellulose blown on an attic floor, or of R-49 worth of dense packed cellulose in a roof furred down to make space for it.

        If you are going to insulate at the roof rather than the attic floor, this article outlines the options:

        https://www.greenbuildingadvisor.com/article/five-cathedral-ceilings-that-work

        This long article goes over insulation options in general, including disadvantages of spray foam, in the article and second comment

        https://www.greenbuildingadvisor.com/article/a-beginners-guide-to-insulation

        If you go ahead with spray foam, do specify HFC-blown foam, for better performance, easier installation of a thick layer, and lower climate impact. And get in writing what the companies policy is if the foam doesn't cure right, especially likely in winter, and your house has a persistent odor problem.

        As for the heating system, well, the good news is that if you do the envelope really well, the heating system needn't bee that big.

  3. Expert Member
    AKOS TOTH | | #7

    As soon as you say hydronic, you are adding about $20k in material cost plus a lot of labor to the build. Depending on the marker and expectations, that might or might not be a lot.

    Since you need AC, you'll have to run ducts, so at that point might as well use it for both heating and cooling.

    The exception to this, it is very nice to have heated floors in entrance mudroom, kitchen and bathrooms. This can easily be done with electric resistance mats under the tiles.

    Your energy source and costs will set what makes financial sense. I'm in the land of cheap natural gas and expensive electricity, so gas dominates. Well designed heat pump comes in pretty close though, so it is worth it from the green perspective.

    For actually heating and cooling a place like that, you are probably looking at two air handlers, one in the basement for the main+basement and one on the 3rd for the 2nd+3rd floor. The important part here is to keep all ducting inside the conditioned envelope, by the sounds of it you are insulating at the roof deck so this is less of an issue.

    Ventilation is always best delivered with dedicated ducting. This tends to add a lot of cost especially with a lot of rooms. The in-between is to share the supply ducting with the HVAC and have dedicated stale air pickups in the house like in the "Multi-Point HRV or ERV with Partial Connection to Central Air Handler" diagram here:

    https://www.buildingscience.com/documents/information-sheets/info-611-balanced-ventilation-systems

    ERV or HRV does not matter much in most climates, either can work well, imporant part is to get a well set up system. I prefer ERV in colder climate as they need to spend less time defrosting and also help keep indoor humidity higher in the wintertime.

    For your insulation options, SPF is usually the best way to seal up older houses with complicated roofs. Doublecheck your code needs as in most places you only need R38 roof assembly, R49 in SPF is a lot more foam for almost no energy savings.

    For the walls, go for open cell foam. There is no point in spraying high R value foam between studs as you loose most of that extra R value from thermal bridging of the studs. A 2x6 wall with open cell SPF and closed cell SPF have almost the same assembly R value (R18 vs R21). Even better, seal up the walls with 1.5" or so of cc SPF and insulate with either batts or dense pack cellulose.

    Make sure to also insulate your foundation in the basement. Getting at least R8 of rigid or 2" of ccSPF on the foundation makes a big difference on energy use. It also keeps the floor of the main level much warmer.

    1. josephny | | #9

      I'm trying to get up to speed from a very very low level of knowledge.

      You write that I "need AC." Do I need it for comfort or for other reasons as well? I would certainly consider not having it.

      And, when you write that by adding hydronic I am "adding about $20k..." am I correct in my understanding that this conclusion is based on having both a system with ducts for AC/ventilation/humidity-control AS WELL AS hydronic? That is, I would be having 2 systems instead of one, thereby adding all that cost?

      Propane is $1.79/gallon and electricity is under $0.10/kwh delivered (but expected to go up). (And I'm also considering a photovoltaic roof system).

      Everything under the roof will be in the envelope. As for SPF, because the rafters aren't deep enough, I was going to fur them out with XPS or EPX, which would help with the thermal bridging.

      I've read in a number of places that wall stud thermal bridging does indeed degrade the over r performance of the wall, but I don't fully understand the mechanism and/or calculation? That is, if I achieve r-25 by between-the-16"-OC-studs wall insulation, and my net r value after the thermal bridging is r-20, what would be the net r value if I has r-20 between the studs? Or r-40 between the studs? That is, what is the mathematical relationship between the r value between the studs and the overall r value as the r between the studs changes?

      But, back to what's important: Do I need a ventilation system? Can it just be some exhaust fans in the bathrooms and some way to bring in filtered air to replace?

      Am I even on the right track to try to simplify this and/or eliminate ductwork?

      Thank you so much!

      1. Expert Member
        AKOS TOTH | | #14

        I can't see living in the west coast area with 100F+himidity in the summer without AC. Possible, but now what I would consider comfortable, personal preference I guess.

        The extra $20k is since it is a reduant heating system. If going with hydronic only, it would be less but still more than equivalent airhandler+ ducts.

        Your $1.80 propane burned in a 95% boiler works out to $2/therm. The $0.10/kWh electricity feeding a COP 3 (seasonal average for a good hyperheat unit) heat pump works to $1.02/therm so heating with heat pump is about 1/2 the cost of propane.

        For wall assembly R values, the easiest is to run your options through this site https://www.ekotrope.com/r-value-calculator

        Don't get too caught up in R values though. An R20 wall VS an R22 wall is noise in terms of energy use. Focus instead on getting a robust, well sealed assembly. That will make a bigger difference in terms of building durability and occupant comfort.

        Even a less well sealed house will need good ventilation. Exhaust only ventilation only works on paper, the fresh air is brought in through the air leaks in the house, which rarely if ever where people are. With a down to stud reno you are doing, the additional cost is noise for the overall budget and will make a big difference on indoor air quality when done. It does have to be though of and designed in from the beginning, don't leave it as an afterthought.

        1. josephny | | #15

          I just checked with the boss and she confirmed AC is a must. Oh well, so much for savings...

          I don't think $20k extra for the hydronic would make sense for me. Now I understand that the extra cost is to have a second (redundant) heating system -- thank you.

          I am leary of heat pumps. My zip is 12763. I have another small home/cottage just up the road from the house under discussion and installed a Pioneer heat pumps. It completely fails to keep the place (spray foamed) warm in December-March. I understand Pioneer is far from the best brand.

          As for ventilation: Sounds like I absolutely need it.

          Do I understand correctly that all this narrows my (wise) options to either a mini-splits plus a separate ducted vent system or a single heat/AC/ventilation/humidity-control system?

  4. charlie_sullivan | | #8

    You are right that hydronic adds cost, and so a forced air system might be the way he wants to go, but you *can* have A/C without running ducts. Ductless minisplits, or wall-mount chilled water fan coils that are like miniplit heads but much slimmer. Then you can have the silent heat delivery of a hydronic system in the winter.

    Then the ducts for the ventilation system can be much smaller than the ducts would need to be for heating.

    1. josephny | | #10

      So, a wall mounted AC unit in each room? That would provide AC, but not ventilation, right?

      1. charlie_sullivan | | #12

        Not necessarily in each room. For example, for my New Hampshire house, I have one in the living room only. I cool the living room a little more than needed, and the bed rooms at the far end of the hall still get sufficiently cool and dehumidified. I'm not sure how our summers compare--if you are up in the hills enough it might be pretty similar. You might be happy with two per floor, for example.

        And yes, those would provide A/C--cooling and dehumidification, but not ventilation. I see that as a good thing--your ducts for ventilation can be smaller than would be needed for A/C.

    2. Expert Member
      AKOS TOTH | | #11

      Find a good hydronic installer is hard enough. I recently had a lengthy discussion with an experienced hydronic professional who insisted that primary/secondary loop setup by itself is condensation control for the boiler (which was "right sized" at 200 000 BTU).

      Now you add in air to water heat pump, buffer tanks, multiple hydronic air handlers. The number of people that can design, install and properly commission this is so small that the chances of it being done right approaches zero.

      As an engineer, I would like the challenge of getting a system like that working and tweaking to get the highest efficiency. Not sure any homeowner would care.

      They just want heat and cooling without any headaches. A simple geo with a single central air handler is already too much headache for most.

      1. charlie_sullivan | | #13

        Can confirm. As an engineer, I have enjoyed tweaking my system, but have found it incredibly frustrating to try to find tradespeople to work on it.

    3. josephny | | #16

      Do I understand that a possible solution is ductless minisplits, radiant, ducted ventilation?

      My guess would be that this would be substantially more labor intensive and therefore expensive. I understand the benefit of the hydronic heat, but what is the benefit of minisplits and ducted ventilation instead of a single forced air AC/ventilation solution?

      1. charlie_sullivan | | #20

        Yes, that's an option. The advantages are smaller ducts and the lack of the complexity of trying to integrate the cooling and ventilation, which is something that is hard to get right.

        If you want radiant floors hydronic heating, the cheapest/easiest thing to find people to install might be propane for the floors, and get several Panasonic Intellibalance ERVs. (You could get one large one for the whole house, but the Panasonic ones and nice and reasonably prices and you'll have shorter ductwork if you use several of them located in different parts of the house.) Then a few minisplits--your open floor plan works well with that.

        You can swap in a heat pump to supply the radiant floor in a few years when more contractors have had experience with that and when there are more incentives in place to more things in that direction.

        Only thing is, your electric vs. propane costs now would make running the heat pump about half the cost of the propane heat! So it's kind of a shame not to go there right away. If you get minisplits with cold-climate heating capability, you could supply some of the heat with them and some with the radiant floors and save some money that way. Especially use the minisplits for when it's unoccupied.

        1. josephny | | #21

          I am really hoping that the cost to heat this tight house with radiant will be quite reasonable, whether propane or heat pump (obviously, lower is better). I would be okay with a heat pump if someone with expertise and authority could verify it would work well in this zone 6 area.

          Same with minisplits -- and having them as backup heat would be nice.

          Do you really think I need an ERV (or HRV or any ventilation)? I see online (mostly here) that there are many levels of thoroughness one can have for ventilation. I wonder if just a couple of the Intellibance units in the house would work well (that is, none in any of the bedrooms) -- perhaps just as a way of getting make-up air inside?

          Thank you!

  5. josephny | | #17

    So what would you all do with this gut reno?

    Hydronics for heating and separate forced air for AC/ventilation?

    Hydronics for heating and cooling?

    Forced air for heat/ac/ventilation?

    HRV/ERV & humidity control?

    3 floors, 7 bedrooms, 3 full and 2 half baths, entirely open floor plan for 3rd floor, half of 1st floor is open floor plan, about 850 sq-ft of glass for windows & doors.

    Thank you!

  6. billfrombirchwood | | #18

    I would hire an independent HVAC design company to perform a Manual J for heat loss and provide several options based on your budget. They will request a copy of your floor plans and the load them into a CAD package such as WrightSoft. The package will do the manual j and allow them to layout your options. WrightSoft can do both hydronic and duct work.

    Once the design is done, then interview the installation companies and review the design that has already been done. The install company will then prepare an estimate base on the bid package prepared by the designer.

    Then look at your budget and the estimates to make an informed decision.

    1. josephny | | #19

      Thank you. I wish I could do that. If I were in or near a densely populated area, I'm sure I could find 2 or 3 competent companies (coming referred).

      Unfortunately, there is a major scarcity of all forms of service providers where I am, let along people highly skilled and current in HVAC solutions.

      EDIT: I just realized that an independent HVAC design company might not have to be local. Any recommendations?

  7. ben1350 | | #22

    Try David with Consult air.https://loadcalculations.com.
    He has done a couple of homes for me in Idaho and Montana.

  8. Expert Member
    AKOS TOTH | | #23

    Your Pioneer mini split did not work because it can barely be called a heat pump. The unit's output drops significantly even in milder temperatures.

    A proper hyperheat unit will maintain rated output down to 5F temperature most will provide 80% rated down to -5F. Properly sized, they will have no problem heating your home.

    Once you have your load numbers, browse through here:

    https://ashp.neep.org/#!/product_list/

    You are looking for single zone centrally ducted units. Stuff like Mitsubishi Zuba, Daiking SkyAir or Carrier Greenspeed.

    1. josephny | | #24

      The HVAC company that sold me and installed the Pioneer swore up and down that it would keep the place toasty -- and they were local, so ignorance of the climate is not the explanation. Ugh.

      I did a Slant/Fin and Manual J analysis (as best I can, which is probably somewhere between majorly flawed and somewhat flawed) and Slant/Fin says the house will have a 61,000btu/hr heat loss; manual J using coolcalc yields heat load of 76,000btu/hr and cooling of 28,000. I'm sure I messed it up -- I'm working on understanding exactly what each field means.

      I keep coming back to wanting a solution without vents. Something like hydronic heating in the floors and minisplits for AC and backup heating?

      But that doesn't include a solution for ventilation or humidity control (beyond the minisplit AC's secondary benefit of reducing humidity).
      Then I came across hydronic cooling....

  9. billfrombirchwood | | #25

    John “Siggy” Siegenthaler Appropriate Designs is out of New York State may be able to do a design he is the Dean of Hydronics. I used his books for my own hydronics system, it was a good review of basic engineering, For warmboard, the carpenters installed most of it it, and the plumbers finished it. I installed the controls and calibrated the heat exchanger.

    For my own duct work, I hope to use Energy Vanguard, they seem to understand proper ventilation. I grew up with hydronic heating, so that I understand. There still is an art to duct work , that requires some experience. Dr. Bailles posts here on GBA, so will hire Energy Vanguard after the framing plan is ready. Vent work if properly designed is comfortable, quiet, and improves indoor air quality. Vent work can also be noisy, drafty, and dirty if you don’t pay attention to details.

    If you look at SpacePak, they use hydronics cooling for their mini splits, hi-velocity uses hydronics for AC. Different application of the same physics, water moving energy.

    Again my intent is to reduce the number of things that can break and keep things as small as possible.

  10. josephny | | #26

    Wow!

    Appropriate Designs, Energy Vanguard and SpacePak are all so cool (no pun intended) and hot (pun intended) -- okay, okay, those are some impressive bodies of knowledge and applications of current technology.

    I love the summary of 'why hydronics' -- so clear and persuasive.

    But, like you, I feel strongly about keeping this small and simple.

    Despite my stubborness, I keep coming back to the need for ducts in order to satisfy ventilation and humidity-control. Am I missing something?

  11. billfrombirchwood | | #27

    Some sort of duct work is needed to move air through the building, I.e. ventilate. An ERV or HRV maybe all you need.

  12. josephny | | #28

    I'm pretty sure I'm being slow on this -- my apologies. I keep going around and around and nothing is jumping out as the best solution.

    Some options:

    1. A single HVAC system that provides heat, AC, ventilation via an HRV or ERV, and humification/dehumidification provided by galvanized ducts. Benefits: less physically intrusive, fewer things to break/maintain, lowest cost. Cons: Potential for noise via vents, pollutants/dirt collection, limited zone capability; or

    2. Hydronic heat AND an centralized AC/ventilation/humidity-control systems w/ducts. Benefits: Heat in floor and silent where it's best, visibility for AC/ventilation is only vents which can be placed to optimize AC/ventilation. Cons: Double system, double cost; vent potential for noise and pollutants; or

    3. Hydronic heat, AND mini-split ACs (i.e. ductless), duct system (albeit smaller ducts that might not need to go to every room) for an ERV or HRV. Pros: Great heat; individual room control for AC. Cons: Many things to break (unit for each room), aethestics, still have duct potential problems; or

    4. Mini-splits for heat and AC, with an HRV/ERV duct system. Pros: Low costs. Cons: aethestics, many things to break, ducts; or

    5. I could just skip the ERV/HRV and use fans for ventilation. Pros: No ducts to worry about. Cons: Fresh air problem.

    I really need to make a decision soon on this.

    What would you all do?

    Thanks!

    1. charlie_sullivan | | #29

      Thanks for summarizing.

      Note that on option 3, you do not need to have a minisplit head in each room, particularly given your modest cooling requirements (if I remember/understand right).

      1. josephny | | #30

        Do you mean that some rooms simply won't have a head (fan unit, right?), or that I might choose a multi-split system (ducts)?

        Yes, I would say the cooling requirements are modest.

        I've also seen high velocity AC (uses smaller ducts and can have humidity-control and fresh air, either by using an HRV/ERV or just a vent, share the ducts).

        Too many choices for a non-pro. And the local pros all want to install their flavor of the year.

        1. charlie_sullivan | | #33

          Could be either or both. For example, if you have a head in the hallway you can cool the whole floor while the doors are open during the day, and then if you close the bedroom doors at night, it's not a problem since the heat load is less at night and you have pre-cooled.

          I'm not a fan of high-velocity ducts. If your cooling load is modest, your ducts can be small without incurring the extra energy costs and possibly noise of using high velocity airflow.

          Have we already talked about hiring a designer independent of your local installers?

  13. Mark_Nagel | | #31

    I'll offer this as a place to help find a baseline:

    https://www.phius.org/PHIUS+2021/PHIUS%202021%20Prescriptive%20Project%20Specific%20Calculator%20v1.45/PHIUS%202021%20Prescriptive%20Project%20Specific%20Calculator%20v1.45.htm

    An aside: When discussing things with your wife/partner, always make it clear that there WILL be compromises in the design and solutions. Endeavor to hammer the heck out of things up-front so that later on you can both take credit and blame (rather than pointing fingers). Cost is an obvious means of forcing compromise: but just make sure that all parties fully understand what is being compromised. Successful delivery of "needs" will almost never produce bad outcomes, whereas the successful delivery of "I want" not necessarily so.

    1. josephny | | #32

      Thank you. I can't say I fully understand what this calculator is telling me.

      After inputting the variables, the results are:

      Ductless Heat Pump:
      Minimum HSPF: 10.0
      Minimum COP @ 5F: 1.75
      Minimum SEER: 15.0
      Minimum EER: NR

      Single Package ASHP:
      Minimum HSPF: 9.0
      Minimum COP @ 5F: 1.75
      Minimum SEER: 15.0
      Minimum EER: NR

      Thanks!

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