I love a good wood fire. In our new SIP house I'm looking at putting a small wood burning stove in the main living area, on an east or south wall. The stove is a model with integral legs and will be sitting directly on the polished concrete slab and will have ceramic wall tile behind. What is the best solution for wood stoves in a tight SIP house, vent/heat outside air, or fan-assisted venting through the upper pipe? I want to avoid backdrafts. JHinson

What I did in my SIP house was to install a Fireplace Extrordinair. It comes with a blower that turns on automaticaly when the fire gets so hot. I put the blower outside to bring in fresh air through the heat exchanger to heat the air in the house while pressurizing the house stopping any chance of a downdraft, and with the blower, it does a great job of heating the house. And like you. I really enjoy the look and sound of a fire. The only time I have to be careful is when I start the fire, making sure that no bathroom or kitchen power vents are on. Once the blower on the fireplace kicks on, everything is OK. Do you have a whole house ventilation system? If so, make sure it's operating when you start your fire. The problem with a fan assisted flue is that it creates a slight vacuume in your house and pulls in cold air through every nook and cranny actually making it more expensive to heat your house. Something else to keep in mind is that for some reason, wood burning stoves seem to have more problems with creosote buildup than fireplaces. It may sound like I sell fireplaces, but I don't, I sell SIP's. Have a great day, Steve

Steve,

What happens when the power goes out?  Can you keep the fire going?  I am considering a woodburning stove (HearthStone) and using a small a tube (similar to dryer vent on outside wall) to allow air into the stove from outside.  With insulation around the tube and a cut-off at the stove, it should seal okay when not burning.  Does the tube need a positive pressure or would the negative pressure in the stove be sufficient to draw?  I suspect the latter should be sufficient.

Tim

Tim,

The fireplace came with a screen so that you can have a fire and enjoy the look and sound of a wood fire. There is a switch so that the blower only operates with the doors closed. So, if the electricity goes out, I can open the doors, put the screen in front of the fireplace to stop sparks and still heat the house.

I think your idea of a duct for fresh air to the stove should work fine. I would have the damper closed when I start the fire, close the stove door and then open the damper. I would also suggest putting the damper as close to the outside wall as you can, keeping the cold outside air as far from the inside of your house as possible and preventing birds or animals from building nests in the duct. A screen on the outside of the duct will help this too. The only drawback that I can see is that this would be pretty manual, and would call for close supervision. When the fire goes out, you would have to make sure to close the damper so cold air wouldn’t be drawn into your house. You might be able to find a thermostatically operated damper that would open when the fire got hot enough and close when the fire went out, but that would entail some expense and wiring. I’m not sure if one of those hanging flappers (like on a dryer vent, only backwards) would work very well. The nice thing about a manual damper is that you would be able to control the burn rate. That’s one of the things I like about my fireplace. There’s a heat sensitive switch that turns the blower on and off and an air control to control the burn rate.

A couple of things to think about. A blower will help circulate the heat around your house for a more all house even heat. You might put a ceiling fan over the stove area to help distribute the heat. Wood burning stoves seem to have more problems with creosote build up. I think wood burning stoves do a better job of converting wood to usable heat than a fireplace.

Steve Etten
[email protected]
www.GrandCountySIPs.com

Steve,

Thanks for the information and feedback.  I took a look at their web site.  Too bad they don't offer a free standing wood stove.  I prefer those for increased radient heat.

I mentioned the dryer vent more with reference to the rain/wind cover than the hanging flapper.  However, our current house also has a manual damper on the inside of the dryer vent.  Blocking outside air opens the tube to inside air.  Something like this might work if it were accessible.    I guess that with a flexible cable attached to the damper lever, it could be made accessible even if buried in a wall.  For our next house, I am inclined to use a 2" tube, wrapped with insulation or boxed with blown in insulation, running through the crawlspace with 1/4" mesh and a rain/wind cover at the outside termination.  That tube would terminate on the inside at the 'outside air supply' connection on the wood stove.  There would only be a free flow of air into the stove, but not into the room, at least not directly.  A lever on the stove controls air input and burn rate.  With an 8 hour burn time and 12 hour sustained heat time on something like the HearthStone Heritage model, hopefully, there would not be much unattended time for there to be heat lost through the stove after a fire went out.

As for heat circulation, I am planning to set an EcoFan on top of the wood stove.  It is powered by a heat differential motor (no electric connection).  I bought one last year for my mother to use on her wood stove insert.  It seems to work very well.

For better heat distribution, I am thinking of putting the wood stove in a central location in a square or almost square house.  This would entail running the chimney straight up through the roof.  One thing I do need to figure out is how to vent the double wall chimney pipe through a vaulted ceiling SIP roof.   Can this be done with exposed pipe or should it be boxed?  Any thoughts on this?

Thanks.

Tim

Tim,

Probably the best thing to do would be to contact the wood stove supplier and pick their brains. On my fireplace, the airspace between the inner and outer walls of the double wall chimney pipe is vented to reduce outer wall temperatures, so mine was a little easier to do. Basically, find out what clearance you need between the outer wall of the chimney pipe and any combustibles, and cut a hole in the roof to satisfy this requirement. The ESP isn’t flammable, but the OSB is. Check with the supplier, but I think you can fill the void with fiberglass insulation, put maybe a thin copper plate around the chimney pipe against the ceiling on the inside to cover the hole and a storm collar and flashing on the outside. There’s special chimney caulk that you can use around the seams where the chimney pipe and flashing meet. I think the copper with the black pipe would look pretty nice. If you do decide to go with copper, polish it well and spray it with lacquer or polyurethane to keep it looking nice before installation. And the exposed pipe will radiate extra heat into your house.

Steve Etten
[email protected]
www.GrandCountySIPs.com

Steve,

Thanks for the feedback and ideas.  The copper on black would look very nice.  I like the vented pipe idea.  That might add some convection, especially with the height of a vaulted ceiling.  The placement of the upper vents might help blow heat into the loft area.

Thanks again.

Tim