Attic ventilation with open-cell spray foam
Before I moved into my new home two years ago, open-cell spray foam was installed in the unfinished attic. There is no ventilation in the attic, and the air is toxic up there. I had it tested. (The VOCs may or may not be the spray foam.) My contractor says to use an HRV (heat recovery ventilation thing) but two brands (Broan and FanTech) say these units are not to be installed in space that doesn’t have conditioned air. The drain pan can freeze or the motor can overheat. So, basically, no go on the HRV? Would it be better to install simple (cheaper) ridge vents which will of course defeat the purpose of the insulation? Or is there an exhaust fan system that I could operate on a weekly schedule to clear the air without sacrificing energy efficiency continuously? Need to come up with a plan so I’m not living with toxic air above my head. I need to get to the attic to change air handler filters and mouse traps and suitcases. Thanks.
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A 20cfm continuous exhaust fan designed for bathrooms ducted to a soffit would do the trick.
The Panasonic FV-04VE1 single-room ERV might do it too, if balanced ventilation with some heat recovery is a goal.
Ceramic core single room HRVs that switch direction every 30-100 seconds are not a good idea, since pressurizing the attic space even intermittently would drive at least some of that air into your conditioned space.
A ridge vent would also drive some of that attic air into the conditioned space depending on wind direction, or even from opening & closing exterior doors- the opposite of your goal here.
Super helpful, Dana Dorsett! Thank you. Do you think the continuous exhaust fan would defeat the purpose of the insulation--or not a big deal? (I suppose not if the seal between conditioned space and the attic is good.) I definitely prefer this idea or the Panasonic ERV because I most definitely do NOT want to drive any attic air into conditioned space, so of course the HRVs you mention here and the ridge vents are out! My respiratory health is more important to me than energy-efficiency in this situation. Thank you very much.
The specific heat of dry air by volume is about 0.018 BTU/cubic foot per degree F. A fan moving 20 cfm is moving 1200 cubic feet per hour. So when it's 25 F colder outside than inside than inside it's losing 0.018 x 1200 x 25F= 540 BTU/hr.
To put that in perspective, that's about the amount of heat emitted by two sitting human couch potatoes while conscious. (It drops to about 460 BTU /hr if they fall asleep with the TV remote in their hand. :-) )
In short, it's a heat loss, but it is not substantially defeating the purpose of that insulation.
Just out of curiosity, toxic with what? Does the spray foam have a dead fish odor, or is it a residual chemical smell?
Are you sure none of the waste lines or vent lines were interfered with during the foam installation?
Have you checked for dead animals?
Interesting questions, and my oil company asked me some of these. The air-test results were "moderate", not "elevated", but I still want to ventilate the attic. The test identifies the category of VOCs as "paint/varnishes/sealants, with overlap of these ingredients with fuel oil, diesel fuel, kerosene." So I wondered about my chimney, which has a sleeve, but no idea what condition that's in. The spray foam doesn't currently seem to have an odor, and I have a sensitive nose and lungs, but a second-opinion heating guy was just up there and said it smells like the foam to him. My experience that started this whole exploration was that back in May when I turned on the AC upstairs for the first time after winter, I came back upstairs 2 hours later and my walk-in closet and all my clothes smelled of "oil, or something mechanical" for weeks, until I washed the clothes. I wouldn't say dead fish. I also distinctly smelled the odor of sickly sweet mouse poison coming from the attic. I am not at all sure about waste lines or vent lines affected during installation. Whether a dead squirrel or fuel oil, I'm concerned that the smells from the attic were sent down to my bedroom so I'm trying to find an HVAC company to answer my call to check (and seal) the air handler and ductwork. Being unfamiliar with how a dead animal decaying in a confined space might smell, I can't rule that out! Thanks.
I'm not sure what would show up on an air quality test if the odor is from the foam, but two years is a long time to have a lingering odor from a spray foam installation and could be the sign of an install gone wrong. Here is an article on the topic that may be helpful:
https://www.greenbuildingadvisor.com/article/spray-foam-jobs-with-lingering-odor-problems
Thanks. I agree, and perhaps especially with open-cell, which is water-based. So I'm thinking after two years of too-tight attic, all the VOCs from painting, propane stove, etc. are trapped there. But will keep in mind the possibility that it's the foam. I could call the company and ask them to check it!
It sounds like you have your HVAC system in the attic? If that’s the case, are there any hot parts in contact with the foam or some other plastic part? If your heat recently ran before, or ran during, your test, that might be what registered. You should have your HVAC contractor check if anything is getting hot that shouldn’t be.
Spray foam shouldn’t be off gassing for years. Usually a few weeks and you can’t smell anything anymore. If your attic is completely sealed I suppose it may take a lot longer, by then years still seems too long. Ventilating the space might not have to run forever though, maybe run for a week or two and then stop the ventilation, wait a few days, then test again and see if things are significantly reduced compared to your first test.
On the plus side, if your attic is so well sealed that the foam smell is still there, then it’s probably not leaking much and at least you’re not breathing it inside your living space.
Bill
Yes, two air-handlers, one in attic. What started me on this project was when I turned on the upstairs AC last May, after an hour I came to my bedroom and smelled foul oil-type smell plus mouse poison that had been sent down from the attic. So, sealing the air-handler and duct work seems like a must-do! I will install some kind of ventilation in attic eventually. Very hard to get people to show up to do the work, but I'm trying! Thanks for your help, Bill!
I realize this post is 5 years old, but I am curious if you ever solved your issue. We recently did an indoor air quality test and had the same results. Strong smell and high VOC in the home - open spray foam throughout the house. Did venting the attic help?
I had open cell in my last house, and it still had an odor after four years. But like JcEssex, I have a sensitive noise and even normal smells bother me a lot.
JcEssex. If the air handlers are made out of duct-board, I would replace them with sheet metal. Duct-board can host a variety of things that you don't want blowing through your HVAC system.