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Community and Q&A

Ventilation retrofit in cold Winter and hot humid summer climate

TomK_WI | Posted in Mechanicals on

I’m looking for some advice on how to handle the ventilation of my 6 year old house. It is not a high performance build however it is well sealed.


I’m in the process of finishing about 1000 Sq Ft. in the basement and I’d like to take this opportunity to improve the ventilation, comfort, and efficiency of the house. I’ve been working to better air seal the basement over the past few years and after I sealed my sump, basement floor, and added a radon system I noticed my hot water heater was backdrafting. I’ve since changed to a tankless direct vent. I also noticed that my air handler is drawing quite a bit of air through the 6″ fresh air duct. There has to be a better way than letting freezing winter air or hot/humid warm air directly into the house. I plan on running my air handler fan continuously to even out the temperatures between the two floors.

It seems like there’s no perfect solution to ventilation…

Option 1: Do nothing (exhaust only ventilation)

Option 2: Fresh Air System
– Allows too much unconditioned air into the home for me to consider this a viable option
– Don’t want to end up with positive pressure in the house

Option 3: ERV/HRV

– Which system to go with?
I live in Janesville, WI which has quite a different climate than the rest of the state(we have about 150 more Cooling Degree Days than Madison).
Winters can be brutally cold and Summers are very hot and humid. You can count on one hand the number of days you can actually have the windows open in the summer. I’d say climate is much more like 5A than 6A

Would keep out much of the summer humidity but I am afraid of too much humidity in the winter. After air sealing the basement we usually sit at around 30% to 35% RH in the winter which is too high and causes condensation.

This might dry out the house too much in winter and make it too humid in summer.

– Bath fans
Seems counter productive to continue using bath fans if I install an ERV/HRV but will there be enough ventilation? Say I go with 100CFM, at 60% capacity I could draw 20 CFM from each bath. The article on GBA about this topic cautions use of ERVs.

– Ducting
I think what I’d do is run the HRV/ERV exhaust from all 3 bathrooms then push the supply to the return duct of the air handler.

– Sizing
I’m hearing from some manufacturers that I need 240 CFM of ventilation. That seems waaay too high. I think I’d rather roll the dice with the BSC formula of .01 * total sq ft + 7.5 * (Occupants+1) which is better than what I’m getting today.

– Dryer and Range hood
Not much that can be done for these at the moment. Down the road I can go with a condensing dryer. Range hood is rarely used. Will the make-up air be pulled through the HRV/ERV?

Any advice to set me straight would be much appreciated. Thanks!!

Additional Info

Ranch home, single story 1850 Sq. Ft. w/ basement (back wall half exposed). 4 Bedroom, 6 occupants.

Wall System
– 2-coat veneer plaster on 1/2 blue board
– Poly sheeting air barrier
– Foam sealed penetrations
– 2×4 walls
– Anderson 400 series casement windows
– R13 Fiberglass batts
– Tyvek barrier
– 1″ XPS (not taped)
– Vinyl Siding

– Hip
– 6/12 pitch
– Engineered trusses
– Energy heels
– Soffit and ridge venting
– R50 loose fiberglass

– 1′ wide x 10″ tall concrete footing with form-a-drain
– 8″ wide x 9′ tall basement walls
– 1″ XPS on exterior of basement walls before backfill
– Foam sill seal
– PT rim plate
– Engineered rim joist
– Spray foam sealed rim and verified by depressurizing house with 600 CFM fan

Basement Floor
– Poly sheeting
– 4″ concrete
– Sikaflex all expansion joints, cracks, and corners
– 200 CFM Radon fan
– Air sealed sump cover

– Forced Air single-stage direct vent furnace w/ AC
– April Air 600A Bypass Humidifier (not used)
– Tankless high efficiency water heater
– Passive fresh air duct to return trunk w/backflow damper

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  1. Expert Member
    Dana Dorsett | | #1

    Is the 1" XPS the only foundation insulation? Does it stop at grade, or does it go all the way up to the sill plate?

    You are at the warm edge of US climate zone 6. IRC code-min for basements and crawlspace walls is R15 continuous insulation or equivalent. But in zone 6 the above-grade portion of the foundation wall still needs to more than 1/3 of the total insulation on the exterior side of any fiber insulation. If you're building an insulated 2x4/R13 wall on the interior side of the foundation and the exterior foam stops at grade you'll need at least R7.5 of foam between the studwall and foundation (all the way down to the slab) to meet the IRC prescriptives for dew point control at the foam/fiber boundary. I needs to be set up that way to be able to dry toward the interior- an interior side vapor barrier isn't moisture safe for the studwall, since it traps ground moisture. That stackup would put you somewhat ahead of code minimum for thermal performance, and would be relatively low risk for future mold/rot issues in the finished studwall.

    Also note, that foam shouldn't be 1.5" XPS, which while labeled R7.5, is only warranteed to R6.8. and will eventually drop to R6.3 at end of life as the climate damaging HFC blowing agents responsible for the performance boost slowly diffuses out. EPS is blown with a much more benign pentane blowing agent, most of which escapes the foam and is recaptured at the factory, and it's R-value is stable over time. It would take 2" (R7.8-R8.4 depending on density) to meet the IRC prescriptive. Alternatively 1.5" polyisocyanurate board could be used (labeled R9),. which is also blown with low-impact hydrocarbons.

    In your locations the subsoil temps are low enough that 1" of EPS (not polyiso) on the floor would be a good idea for keeping summertime mold issues in rugs or boxes stored on the slab, even 2" could still be financially rational on a full lifecycle basis.

    An ERV is not a dehumidifier- go with an HRV, and back off on the ventilation in summer when outdoor dew points are high. The cooling loads of basements (insulated or not) are too low to count on the air conditioning to dry it out- a room dehumidifier may be necessary if you insist on continuous or high rates of ventilation during the sticky-muggy season.

  2. Jon_R | | #2

    With 6 people in 1850 sq ft, you are likely to have excessive Winter humidity. So +1 on a HRV.

    It's best if the HRV supply goes directly to the bedrooms at about 15 cfm/person.

    I'd continue to use bath exhaust fans during showers.

  3. TomK_WI | | #3

    @ Dana Dorset - Yes, exterior 1" foam is continuous all the way from the footing to the roof. The finished basement area is actually 2" XPS with firing strips to support the drywall. That gives me R10 XPS + ~R1 concrete + R5 XPS so if Wisconsin actually adopted IRC I would be within code. It is unfortunate I didn't understand the climate impacts of XPS until after I had used a bunch of it in the basement. :( I hear you on the insulated floor. I almost went with a dimpled foam underlayment with 5/8 OSB to at least get a thermal break with some drainage. 1 or 2 " of XPS would have been good to know about before that slab was poured! OSB underlayment would still need to go over the XPS. If i significantly raise the floor I'll have to shim the stair treads. I still have some time to think about what I want to do here.

    @Jon R - Good point... as mentioned I get condensation on the windows in the winter. It turns to ice if I close the cellular shades all the way. Thanks for the vote.

    Does anyone else have ideas, opinions, or experiences to share?

  4. TomK_WI | | #4

    I'm finding that a decent HRV is much cheaper than a good ERV. I think at this point if money were no object I would go with the Broan ERV200ECM. It has all-around good stats according to HVI. In fact, I really don't see any competition except for the Zehnder units. $2000+ is tough to justify for ventilation. I was looking into the smaller Broan ERV140TE but the sensible recovery numbers are just garbage.

    I am slightly worried about drying out the house too much with an HRV. I recently sealed my sump and put in a radon system and haven't gone through a winter season yet with the reduced humidity load. Worst case I could just run the April Air humidifier if it gets too bad. In summer I could just make sure the HRV is interlocked with A/C to limit the need for aux de humidification.

    Seems like the best value in HRVs is the Fantech HERO 150H-EC. Running on low speed it has fantastic sensible recovery #s and is a top performer in Watts/CFM. The Broan HRV160TE looks like a decent second choice.

    After doing all of this research it really does make me wonder if all of this is going to save energy in the long run :/

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