Wytze Schouten wrote:I'd like to test an idea with you all.
So we have a vacation home in the woods in the Netherlands, and we are about to install a wood stove in the fireplace. Location: we have a temperate, moist climate (750mm per year) not unlike that of inland British Columbia or Washington state, except we're farther north on the globe, so the sun sits lower and isn't as powerful. Our land is fairly high and dry on sandy soil, but we do have moisture problems in the basement.
Whole house in the woods: https://www.dropbox.com/s/o2v72w2h2nihp8q/2013-05-18%2015.18.17.jpg
The fireplace installer technician mentioned the possibility of adding an external air supply to the wood stove. He advised against it, though, because in his experience this is only necessary for very new, highly insulated homes. In those homes, the fireplace would not be able to draw in enough new air through cracks and vents, causing incomplete combustion, underpressure, and other undesirable outcomes. For every other type of home, the recommendation is not to use external air supplies. Recent research online suggests there is not only very little benefit, but also a real risk because of the possibility of backdraught.
I accept this guy's expertise for installing in homes and modern buildings, but not when it comes to wooden vacation homes from the 1920s in the middle of a forest. I have reason to think we might still have a very good use for external air supply in this case.
First of all, the wood stove is calculated to use about 20 cubic meters of air per hour. That's one sixth of the volume of the room where we're installing the stove. So it's not much, but it isn't negligible either. Since the walls are all wood (planks, not logs), the house has very little thermal storage. So the approx 100 kg of air inside the living room is a significant part of its thermal mass. Also, letting the stove take its air from the living room will likely lead to a draught along the surface of the floor, which means cold feet and an unhappy dog. (Plus discomfort for any guests who might be sleeping over on mattresses on the living room floor)
Second, if we install the external air supply and let it take its air from the basement instead of the outside, we are likely to solve two problems at once. The tube would only be around 50cm (1,5 ft) long, or we could lead it all the way to the floor of the basement to make sure it sucks the coldest, moistest air out first. The basement has several big cracks and small vents to the outside. At 20 cubic meters, the basement's air would be fully replaced every hour and a half. This might help a lot with the moisture problem. Currently we can only avoid fungus formation in the basement by leaving the trap door open throughout winter. But ventilating moist air into the vacation home can hardly be called a solution.
I am wondering about three possible risks, some of which have been discussed in the forum on rocket mass heaters by Paul and Erica and Al:
1. Moist air and wood stoves. Taking moist air from the basement to go into the wood stove: how bad is that? I know moist wood is bad, so I'm not confident about this bit. How bad is a supply of moist air for the wood stove's metal parts? The air is preheated by the stove before it reaches the fire: will moisture help it to absorb more heat faster, or exactly the opposite?
2. Backdraught. In certain situations, wind may cause high pressure at the top of the chimney and low pressure in the places where the stove gets its external air. In that case the fire from the wood stove might blow back into the air supply and into the basement. This seems unlikely because the basement is shielded from the pressure changes that might occur around the outside of the house during strong winds.
Thanks to Al for pointing me in this direction.
I'd be happy to hear any thoughts!
Wytze
Basement: https://www.dropbox.com/s/4flhkpqjjc0egsy/2014-05-18%2017.53.59.jpg
Floor above basement: https://www.dropbox.com/s/l2nd1asaxm29tui/2014-05-18%2016.50.13.jpg
I plumbed my intake to pull air from the basement like you suggested. I did it to use the cooler, more humid, Radon rich air. It did help a bit with the Radon gas.
My house is very tight but i have no issues with backdrafts unless we have the bath and kitchen exhaust fans both running when the chimney is cool. Once the chimney is warmed up good no issue.
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