Ventilation and dehumidification strategy for crawl, living, and attic in older home
Hello all,
I have a 1,400 sq ft 1966 home in CZ2 with an encapsulated crawlspace and OC spray foamed roof deck (sealed attic). I have two goals that I should probably address at the same time. First, I’d like to improve humidity management in the crawlspace, living space, and attic. Second, I recently purchased an Aranet4 CO2 monitor and now see the home needs better ventilation. What are some ways to accomplish my two goals?
I currently have a 2-stage heat pump for the living space with a central return closet. This controls humidity well in the summer, but not the other three seasons. I also have a dedicated dehumidifier for the crawlspace and this works well.
From my own research, it seems like a good solution for the main living area is a ventilating dehumidifier like the Aprilaire E100V. I believe the best way of installing this would be in the attic with a dedicated return duct from the living area’s ceiling and a dedicated supply duct to the ceiling of the central return closet. Opinions?
I am less sure about how to manage humidity in the attic. I could install another dedicated dehumidifier, but it seems like there must be a more efficient way of accomplishing my goals beyond having three dedicated dehumidifiers in my small home (crawl, living, attic). For example, if I install a new ventilating dehumidifier in the attic, I could split the dedicated supply and return ducts with wye fittings so that some of the attic air is dehumidified. However, that means I would be mixing attic air with living space air, and I’m not sure if that is a good idea.
Any advice is appreciated. Thanks for reading.
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Replies
If you've insulated those spaces they are now part of the interior of the house and the strategy is to include them in the ventilation of the rest of the house. You can connect them to either a supply or return from your HVAC, they're probably leaky enough to the rest of the house that you don't need both. If the air in there is dusty, do a return and put a filter on it.
Thanks for your succinct and informative reply, DC.
After thinking about this for a bit, I have devised a plan:
1) Install a ventilating dehumidifier in the middle of the attic
2) Install fresh air vent in gable, ducted to the dehumidifier's fresh air intake
3) Leave the dehumidifier's return open to the attic (non-ducted)
4) Duct the dehumidifier's supply to the air handler closet (through the ceiling)
5) Cut two small return grills into the ceiling, one at each far end of the home
If I have thought this through correctly, the dehumidifier should put a small negative pressure on the attic. The return grills in the ceiling will therefore allow air to move from the living space into the attic, where it is mixed and dehumidified with fresh and attic air before being sent to the central return closet.
The mixed/dehumidified air being sent to the return closet will be filtered and distributed through the supply ducts whenever the air handler's fan runs (potentially always if I keep the fan on low/35%).
Does this sound like a reasonable plan?
It seems to me until you can bring yourself to use the words “conditioned attic” and “conditioned crawlspace” and accept that both spaces need to be conditioned to more or less the same temp and humidity as the rest of your house you will continue to look for ban aid solutions to big problems.
Why don’t you want the attic air in your home? If the air in the attic in dirty clean the attic. If the air in the attic is hot remove the old insulation from the attic floor and install enough registers in the attic to keep it cool.
I do not think bringing more outdoor air into your conditioned spaces is the answer to your problems.
Walta
Agreed.
Thanks for your reply. I agree that the proper solution is to condition the crawlspace and attic, and I thought that is what my proposed 5-point solution that I posted above would do. I specifically propose actively mixing the attic air with the rest of the home's air via the dehumidifier and additional grilles connecting the attic to the main living area. Do you see a problem with this proposed plan?
I don't see why you feel the need to put a hole in the gable. An energy-recovery ventilator is what you need if your CO2 is excessive.
I don't see why you feel the need to condition the air of the attic and crawlspace separately from the rest of the house. Condition them all together. If, after doing that, you need dehumidification, a single dehumidifier should be able to handle the entire house. If air is allowed to circulate humidity equalizes pretty readily within the house.
I initially planned on installing an ERV to deal with ventilation. But after watching a series of recent videos on ventilation by "Home Performance" on YouTube, I learned that ERVs are not recommended unless you have a confirmed tight home. Although I have tried to improve my home's air tightness, it is limited by the fact it was built in 1966 without modern materials and methods. With that in mind, a supply-only ventilation approach seems to be the better strategy. Of course, I am more than happy to hear other opinions.
https://www.youtube.com/@HomePerformance/videos
My proposed action plan (above) actively exchanges air between the attic and main living area. The crawlspace would continue to be conditioned separately. I agree that ideally I would condition the crawlspace, living, and attic together as a single space. This would be easy by simply installing a grille that connects the crawlspace to the return closet. However, I need to do some additional work in the crawlspace to ensure it is properly sealed. A local company was hired to seal the crawlspace before I purchased the home and did an OK job, but it needs additional work before I would consider it to be adequately sealed for the purpose of connecting it to my main living area. There is some air and bug infiltration that needs to be sorted first. Until then, I need to condition it separately.