How to heat a crawl space & ventilate it in winter?
NorEasterGirl
| Posted in Energy Efficiency and Durability on
I have a crawl space beneath my home. The floors are freezing and our bills are high in winter. I recently had a very reputable gentleman (ie., expensive but knowledgable) spray closed cell foam along the joists and sealed the space up – it had almost no insulation. Now I am vaguely worried because we heat the space to 50 degrees in winter (we live in upstate New York) but I am reading about off-gassing and thinking – how do I ventilate a space I need to heat in the winter?
Can anyone talk me through this? Thanks so much –
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Replies
Off gassing from spray foam is (or at least, should be) mostly done after several days to maybe a week or so. Exactly how long it takes before you don't smell it anymore depends on the temperature and humidity, and also how much airflow is moving through the space with the spray foam.
I'm assuming from your post that you've already insulated with spray foam, and are just asking about what you need to do for that to be safe. The good news is that it's usually fine, bad installs are fairly rare, and if you had someone who has a lot of experience do the work, that greatly reduces the chances of your having a bad install. If you don't really smell anything anymore, you're fine -- it won't get worse over time, it'll only get better. If you want to ventilate some before winter to be sure, run a box fan or two so that you get crossflow through the space, which means "air in at one end and out the other", with as much seperation between the two "ends" with vents as possible. It's usually preferable to exhaust air, which means setup a fan to blow OUT of the space towards the outdoors. This makes sure you don't blow any stink into your living space. Allow somewhere else (ideally also open to the outdoors, but at the opposite end of the space being ventilated) for air to come IN to the space to replace the air that was blown out by the fan.
You shouldn't need to do anything special with your newly insulated crawlspace over the winter, although you are supposed to allow for some air movement down there. This can usually be done by putting a register in a handy duct somewhere. You don't need much airflow -- you are supposed to allow 1 CFM of ventilation per 50 square feet of crawlspace. For comparison purposes, that would mean the airflow of a typical computer cooling fan would be about the amount of airflow you need for around 1,000 square feet or so worth of crawl space area.
Bill
I'm in upstate NY. I have one register at the end of a run, far from the return air, that I can open. That, and duct leakage makes for acceptable basement/crawl temperature.