Wood fireplace with “posi-pressure”
Does anyone have experience with these fireplaces? I was originally thinking of getting the Apex42 fireplace from Xtrordinair as it was the cleanest burning one I could find. However, the elite https://www.fireplacex.com/product/36-elite/ is about 2k cheaper and advertises “posi-pressure”. On one hand, I’ve read that supply ventilation only may cause moisture being forced through my envelope, but according to https://www.greenbuildingadvisor.com/article/designing-a-good-ventilation-system this isn’t a problem. Does this fireplace then solve the makeup air problem for fireplaces effectively? I’m going to have a very air tight SIP home, so perhaps this fireplace is ideal as the makeup air is included in the installation?
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apparently the fan it uses is 388 cfm. the installation manual is here: https://www.travisindustries.com/docs/93508090.pdf
Is the fan a distribution fan, or one providing mechanically pressured intake air? I get no useful information from their description: "This clean-burning fireplace features our exclusive Posi-Pressure technology that uses fresh outside air to provide optimal warmth by evenly heating your entire home."
If it's providing pressured intake air, that is a closed system and has no effect in interior house pressure. If it's a distribution fan (which is very common), it also has no effect on the interior pressure, but also doesn't help with pressure differences that may cause back- drafting.
Yeah the documents aren’t very clear. But from the way they describe it would be pressurizing the house, it is not for combustion air and this not part of a closed system. It sounds like it’s just a 388 cfm supply fan blowing over the “stove”.
page 25 of this document perhaps has a clearer diagram: https://www.travisindustries.com/docs/98800160.pdf. So it is pulling outside air in and blowing it over the stove with a 388 cfm blower and out into the house to provide their "posi-pressure". The confusing part is from the diagram it looks like this air channel is also exposed to the air going from the firebox to the chimney which seems like a fire and air quality risk.
The way I see it the two options are....a fan draws air from the inside of the house into the unit and it divides between three outlets, two that go through the fireplace and back into the room and one to aid the exhaust out the chimney.....the posi pressure takes outside air to perform the same task.
So drawing from the inside creates a negative pressure in the house....drawing from the outside creates a positive pressure which is what you want in order to prevent infiltration. So what they are saying is if there is an air leak, the pressurized/ warmed air would tend to move in that direction thus bringing the heat to where it is needed.
update: for anyone with the same question, I have decided I do not trust the pos-pressure system and am instead going with the cheaper quadrafire pioneer 2. the emissions are a bit higher, but still under < 2grams/hr for epa cert without needing a catalytic converter. My current plan is to just open a window if needed, and to install a powered makeupair fan later on if it becomes a problem.
page 2 and 5 talk about it more. It doesn't mention anywhere that the air is directly piped into the combustion chamber. The cut-away diagram makes it confusing, but I think all that intake air just gets blown out into the room through the 'decorative grill' (after being heated).
This little bit on the posi-pressure system is a bit... interesting:
"The heated air naturally ‘seeks out’ and penetrates cold spaces, warming the entire home evenly while ‘sealing’ cracks, leaks and other drafty spots by preventing cold air infiltration. "
haha, 'sealing' cracks. Basically it creates positive pressure.
It's curious. I don't quite understand why you wouldn't just want a closed system, and then deal with house ventilation separately. I suppose this allows your inflow to be heated. The outflow becomes the chimney and any other envelope leak.
Ha - missed that! They make the intake air sound like warm AeroBarrier.
that's exactly it Tyler, they are just positively pressurizing the house. Aside with potential issues with interior moisture being pushed through your walls, for a drafty house their marketing claim would seem to be valid, beyond the silly naming. I was looking at it more from the added bonus of not needing to add makeup air to avoid backdraft, since this already has builtin makeup air (and the makeup air is heated).