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ERV, HRV, Fans, Ductwork -- ugh

josephny
josephny Member Posts: 172
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. (I'm exaggerating: Spring/Summer/Fall are quite nice, and the 1200' elevation helps; but December-March is, eh, challenging.)

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 or HRV?

Sure would appreciate some advice.

Thank you!

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 20,440
    Let's assume, for the sake of argument, that you really do manage to get the place really tight (mind your vapour barriers! On the inside side of the walls!!), and that you are going to be able to run amply sized ductwork. If that's the case, then I would suggest a combination. First, a heat recovery ventilation unit integrated with the ductwork. Do NOT get the variety which also recovers latent heat, properly called an ERV. Why? Because, unhappily, it also recovers a good many of the more subtle -- and obnoxious -- indoor air pollutants, which you don't want. Then I would use a heat for the air conditioning and shoulder season heating, also integrated into the ductwork. And I would add humidification and dehumidification capabilities to the mix, also integrated into the ductwork.

    Now that is not going to meet your heating needs when it gets chilly out -- so for that I would go with radiant floors, sized to meet the total heat load of the building on the design day. With a really tight structure, that should be doable.

    I might add... the budget is going to be eye-watering.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Zman
  • TAG
    TAG Member Posts: 738
    How much do you want to spend?

    Spray foaming is what I always do with old buildings ... my current project has radiant/ducted/minisplits -- it's all a question of how far you want to go.

    Years ago I always incorporated a ducted dehumidifier in the system .... with new VS equipment I found that it was not really necessary ... the new equipment being able to remove the humidity even on mild days.

    Old houses leak -- even with spray foam. I'm in a radon zone so I stick with a slightly pressurized house -- simple intake to the ducted system. I also make provision for stove exhaust make up air ... you can always add the dehumidifier if need be.

    The number of people in the house matters as well .... lost of people may require more air changes or humidity control. I prefer using simple proper CFM bath fans vs trying to link them to an ERV/HRV ....
  • josephny
    josephny Member Posts: 172

    Let's assume, for the sake of argument, that you really do manage to get the place really tight (mind your vapour barriers! On the inside side of the walls!!), and that you are going to be able to run amply sized ductwork. If that's the case, then I would suggest a combination. First, a heat recovery ventilation unit integrated with the ductwork. Do NOT get the variety which also recovers latent heat, properly called an ERV. Why? Because, unhappily, it also recovers a good many of the more subtle -- and obnoxious -- indoor air pollutants, which you don't want. Then I would use a heat for the air conditioning and shoulder season heating, also integrated into the ductwork. And I would add humidification and dehumidification capabilities to the mix, also integrated into the ductwork.

    Now that is not going to meet your heating needs when it gets chilly out -- so for that I would go with radiant floors, sized to meet the total heat load of the building on the design day. With a really tight structure, that should be doable.

    I might add... the budget is going to be eye-watering.

    Starting at the end, I'm already crying from replacing the foundation, demoing and disposing of 100 years of accumulated stuff and replacing 1500 sq-ft of 3x10 doug fir floor joists, so, yes, cost is very important.

    Let's assume a pretty decently tight place (no, I have no idea how to put numbers to that, but with foaming the entire envelope, shouldn't I expect pretty tight?). Could I reasonably forgo both AC and ventilation? Just have hydronic heat (pex in the floors) and some through the wall fans and call it a day?
  • josephny
    josephny Member Posts: 172
    TAG said:

    How much do you want to spend?

    Spray foaming is what I always do with old buildings ... my current project has radiant/ducted/minisplits -- it's all a question of how far you want to go.

    Years ago I always incorporated a ducted dehumidifier in the system .... with new VS equipment I found that it was not really necessary ... the new equipment being able to remove the humidity even on mild days.

    Old houses leak -- even with spray foam. I'm in a radon zone so I stick with a slightly pressurized house -- simple intake to the ducted system. I also make provision for stove exhaust make up air ... you can always add the dehumidifier if need be.

    The number of people in the house matters as well .... lost of people may require more air changes or humidity control. I prefer using simple proper CFM bath fans vs trying to link them to an ERV/HRV ....

    What is "VS equipment?"

    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.

    Simpler is much preferred, all else being almost equal.

    I'd prefer to not have to duct, if possible.

    In fact, 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 (;-)?
  • Jamie Hall
    Jamie Hall Member Posts: 20,440
    josephny said:

    Let's assume, for the sake of argument, that you really do manage to get the place really tight (mind your vapour barriers! On the inside side of the walls!!), and that you are going to be able to run amply sized ductwork. If that's the case, then I would suggest a combination. First, a heat recovery ventilation unit integrated with the ductwork. Do NOT get the variety which also recovers latent heat, properly called an ERV. Why? Because, unhappily, it also recovers a good many of the more subtle -- and obnoxious -- indoor air pollutants, which you don't want. Then I would use a heat for the air conditioning and shoulder season heating, also integrated into the ductwork. And I would add humidification and dehumidification capabilities to the mix, also integrated into the ductwork.

    Now that is not going to meet your heating needs when it gets chilly out -- so for that I would go with radiant floors, sized to meet the total heat load of the building on the design day. With a really tight structure, that should be doable.

    I might add... the budget is going to be eye-watering.

    Starting at the end, I'm already crying from replacing the foundation, demoing and disposing of 100 years of accumulated stuff and replacing 1500 sq-ft of 3x10 doug fir floor joists, so, yes, cost is very important.

    Let's assume a pretty decently tight place (no, I have no idea how to put numbers to that, but with foaming the entire envelope, shouldn't I expect pretty tight?). Could I reasonably forgo both AC and ventilation? Just have hydronic heat (pex in the floors) and some through the wall fans and call it a day?
    What was the matter with the floor joists?

    You simply have to define your goals. Do you need AC and ventilation? Actually, depending on where you are and what the usage is, most likely not. Florida? Southern California? Lots of very beautiful people? You probably do. Otherwise... not so much.

    In which case... use a good heat loss calculator (Slant/Fin's, here: https://www.slantfin.com/slantfin-heat-loss-calculator/ is easy to use and very good). and from that determine the heat loss in the various rooms. Then figure out -- can you actually deliver the heat you need from the radiant floors alone, or will they need some boost? If so, can you use panel radiators operating at low temperature?

    And stop right there -- you've just cut your budget at least in half!
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • josephny
    josephny Member Posts: 172

    josephny said:

    Let's assume, for the sake of argument, that you really do manage to get the place really tight (mind your vapour barriers! On the inside side of the walls!!), and that you are going to be able to run amply sized ductwork. If that's the case, then I would suggest a combination. First, a heat recovery ventilation unit integrated with the ductwork. Do NOT get the variety which also recovers latent heat, properly called an ERV. Why? Because, unhappily, it also recovers a good many of the more subtle -- and obnoxious -- indoor air pollutants, which you don't want. Then I would use a heat for the air conditioning and shoulder season heating, also integrated into the ductwork. And I would add humidification and dehumidification capabilities to the mix, also integrated into the ductwork.

    Now that is not going to meet your heating needs when it gets chilly out -- so for that I would go with radiant floors, sized to meet the total heat load of the building on the design day. With a really tight structure, that should be doable.

    I might add... the budget is going to be eye-watering.

    Starting at the end, I'm already crying from replacing the foundation, demoing and disposing of 100 years of accumulated stuff and replacing 1500 sq-ft of 3x10 doug fir floor joists, so, yes, cost is very important.

    Let's assume a pretty decently tight place (no, I have no idea how to put numbers to that, but with foaming the entire envelope, shouldn't I expect pretty tight?). Could I reasonably forgo both AC and ventilation? Just have hydronic heat (pex in the floors) and some through the wall fans and call it a day?
    What was the matter with the floor joists?

    You simply have to define your goals. Do you need AC and ventilation? Actually, depending on where you are and what the usage is, most likely not. Florida? Southern California? Lots of very beautiful people? You probably do. Otherwise... not so much.

    In which case... use a good heat loss calculator (Slant/Fin's, here: https://www.slantfin.com/slantfin-heat-loss-calculator/ is easy to use and very good). and from that determine the heat loss in the various rooms. Then figure out -- can you actually deliver the heat you need from the radiant floors alone, or will they need some boost? If so, can you use panel radiators operating at low temperature?

    And stop right there -- you've just cut your budget at least in half!
    The house sits at the bottom of a rather large hill. We get lots of rain (NYC gets its water from our reservoirs). The ground is clay and rock. Put that together with a 100 year old house that had been neglected for many years and it results in 4' of standing water in the basement for some number of years before I even bought it. Foundation walls shot. Every single 1st floor floor joist rotten. Oddly enough, everything structural above those joists is totally solid -- no rot, no mold, looks kinda pristine.

    My problem is (like so many), I read stuff on the Internet and start to worry.

    If I can have a perfectly healthy house without AC, I'm good with that.

    If I can have a perfectly healthy house without ventilation, I'm great with that.

    Thanks!
  • Jamie Hall
    Jamie Hall Member Posts: 20,440
    Pity about the floor joists -- but you gotta do what you gotta do. I'm not that surprised that everything else is good that way -- say what you will about 100 years ago, but the quality of lumber was a lot better! Even in cheap houses.

    Were you able to do anything about the drainage problem when you rebuilt the foundations? I hope so!

    If you really are doing a thorough job of insulating, you will probably be fine on ventilation -- it's almost impossible to retrofit an old house to be too tight (almost impossible...). And you may well be able to manage entirely with radiant floors. A commonly accepted limit for them is 20 BTUh per square foot of open floor area. If that won't be enough (do do the heat loss calculation!) a very good arrangement is one zone for the radiant floors, and another zone for panel radiators. The radiant floors are slow to respond, but the panel radiators are much quicker, so you can have some setbacks or variations in heat (such as a nice warm bathroom!) without trouble. You can power the whole thing with a mod/con boiler, too, if you have gas available.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • josephny
    josephny Member Posts: 172

    Pity about the floor joists -- but you gotta do what you gotta do. I'm not that surprised that everything else is good that way -- say what you will about 100 years ago, but the quality of lumber was a lot better! Even in cheap houses.

    Were you able to do anything about the drainage problem when you rebuilt the foundations? I hope so!

    If you really are doing a thorough job of insulating, you will probably be fine on ventilation -- it's almost impossible to retrofit an old house to be too tight (almost impossible...). And you may well be able to manage entirely with radiant floors. A commonly accepted limit for them is 20 BTUh per square foot of open floor area. If that won't be enough (do do the heat loss calculation!) a very good arrangement is one zone for the radiant floors, and another zone for panel radiators. The radiant floors are slow to respond, but the panel radiators are much quicker, so you can have some setbacks or variations in heat (such as a nice warm bathroom!) without trouble. You can power the whole thing with a mod/con boiler, too, if you have gas available.

    Oh yes, indeed!

    Dug down deep around the house. Replaced footers with 3.5' wide by 2' rebar reinforced poured concrete footer. Then poured a 12" thick, 7' high wall rebar concrete wall. Then used Deco Seal 20 waterproofing (proof, not resistant). Then put 1" XPS on exterior of wall (wish I had put 4" and been done with insulation needs of basement, but I didn't know). Then put non-woven fabric on ground from edge of footer, 3.5' out from edge and then up to grade level. Then 6" slotted perforated pipe, all the way around and out to daylight by the road. Then filled it with #3 and #4 clean stone up to grade. Then wrapped the fabric over the top. Carried this trench exactly as described down both sides of house and continued down to the road (which luckily is a slope away from house).

    Here's some pics:

    https://ibb.co/QnxNhvR
    https://ibb.co/sK3gph1
    https://ibb.co/17xX51v
    https://ibb.co/vcjFKXG
    https://ibb.co/F7Hp9yS
    https://ibb.co/k9nTSx2

    Insulation contractor says he'll use Heatlok HFO r49 (7") on inside of roof and r25 (3.5") on walls and 4" on rim joists and 2" on basement walls.

    I feel like, while I've increased my understand tremendously, I still don't know what to do about heat/ac/ventilation/humidity. I'm just not particularly excited about installing ducts or mini-splits.

    And I'm told by the boss (mrs.) that AC is a must.
  • Jamie Hall
    Jamie Hall Member Posts: 20,440
    Happy wife, happy life. If it were mine to play with, I'd still go with radiant floors as my base heat source. I would try to avoid ducting -- so, for the AC (and might as well throw the heat pump capability in there too -- not much more money) I'd go with minisplits. The interior heads aren't all that intrusive, and they do do a good job of air conditioning and an at least so-so job of heating, and they completely eliminate the need to have ductwork all over the place.

    Humidity is a potential problem, and it depends very very much on how tightly you want to control it. The minisplits would go some way towards keeping it under control in the summer -- just as any air conditioner would -- but they can't drive it really low; they don't get cold enough. On the other hand, neither they not the radiant floors (nor, for that matter, "normal" forced air) will do anything to raise it in the winter time. It is, in fact, rather difficult to get really tight control of humidity without forced air -- and with the additional (considerable) expense of humidification/dehumidification as part of the package. The budget is beginning to go back up here...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • josephny
    josephny Member Posts: 172

    Happy wife, happy life. If it were mine to play with, I'd still go with radiant floors as my base heat source. I would try to avoid ducting -- so, for the AC (and might as well throw the heat pump capability in there too -- not much more money) I'd go with minisplits. The interior heads aren't all that intrusive, and they do do a good job of air conditioning and an at least so-so job of heating, and they completely eliminate the need to have ductwork all over the place.

    Humidity is a potential problem, and it depends very very much on how tightly you want to control it. The minisplits would go some way towards keeping it under control in the summer -- just as any air conditioner would -- but they can't drive it really low; they don't get cold enough. On the other hand, neither they not the radiant floors (nor, for that matter, "normal" forced air) will do anything to raise it in the winter time. It is, in fact, rather difficult to get really tight control of humidity without forced air -- and with the additional (considerable) expense of humidification/dehumidification as part of the package. The budget is beginning to go back up here...

    So hydronic as the main heat and heat pump minisplits for AC and backup/supplemental heat, right?

    And don't worry about humidity level (AC will lower it in high humid months) or fresh air (open window?)?
  • Jamie Hall
    Jamie Hall Member Posts: 20,440
    You got it. Mow go and persuade the boss...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England