Outside air supply for woodstove in non-airtight house?

[cougkid]

We have a 1914 farmhouse with a woodstove (and oil furnace). I know modern "airtight" homes with woodstoves have external combustion air supplies. Since our house is not airtight, I assume combustion air is being drawn in through cracks. If I was to install an external air supply line, would it eliminate this enough to be worth it?

[Laura]

Drilling an adequate hole or holes in the floor under or near the woodstove or gas heater will draw that under-the-house air instead of dragging those drafts across your feet from the exterior walls and windows. With a localized air supply, your stove will be able to radiate heat and you say goodbye to the cold drafts.

Is it worth it? You bet! It only takes a few minutes and I've done it in every house I've lived in that needed it.

[cougkid]

Thanks Laura! We have an unfinished cement basement below the woodstove. If I was drawing air from the basement, wouldn't the basement fill with cold exterior air from the windows and door in the basement?

[stanb999]

Originally Posted by cougkid

Thanks Laura! We have an unfinished cement basement below the woodstove. If I was drawing air from the basement, wouldn't the basement fill with cold exterior air from the windows and door in the basement?

Well yes. But this may be ok. If your basement is damp. It will help dry it out. I do however have my intake going out the wall behind the stove. Also I've found that the floor in the room with the stove stays toasty warm now.


The big thing to remember with these air intakes is that they are located lower than the floor of the firebox. This is so the stove wont back draft into the air intake.

[Laura]

The following statements are theory and personal experience from a lifetime of heating with wood and stand alone propane heaters and should not be construed as concrete fact.

The theory of locating the air intake through the floor is that underhouse air, especially right under the floor, is warmer than outside cold air and is more stable, not influenced by wind or low barometric pressure which may already causing problems with your updraft. Taking prewarmed air from the basement will create better circulation down there but will not lower the temperature enough to make a difference. For me, it is the easiest method, drill a hole drop in a short pipe with a flip cap on top and a screen on the bottom, calk around it.

Locating air intake through an outside wall leaves it vulnerable to outside wind conditions. Gusts of wind can blow more air in than needed, causing your fire to flare and possibly creating another cold draft if the stove cannot suck all the cold air coming in. If the direction of wind changes, it can cause a vacuum effect, creating a backdraft, especially if your chimney draft is already precarious because of low barometric pressure or being really damped down. I corrected this problem in a house with cement slab floor by extending and elbowing the air pipe to a sink-sized hole in the ground, covering it with a concrete slab then adding the dirt back onto it.

So far, I haven't seen any draft problems that cannot be solved by a localized under-house or undergound air source. It even works on the 150 year old lodges with the giant fireplaces that put out more smoke than heat.

[tamatik]

is there a site with diagrams to help explain this?
Thanx
Gord

[Ross]

Your concern is with house depresurization. it can cause the wood stove and furnace to back draft pulling toxic gasses into your house. Generally speaking an old non-air-tight house does not need a combustion air inlet, and if you add a direct passage for air from your basement to the wood stove or not chances are niether will back draft. Now that said there is an effective method to add a combustion air inlet into your house that will allow a constat re-presurization to occur without needleddly cooling your house through cracks! Simply install a hooded inlet into the basement (above the snow line) and add an insulated flex duct in a sagging loop (called a Saskatoon loop) with the outlet high, closer to the ceiling and a loop of the flex duct drooping to the floor to act as a trap of cold air. Not dis-similar to a plumbing drain trap. It will let cold air in only when the house depresurizes. A ducting of basement air to the stove sure sounds like it would cut off drafts too!

[SmartAZ]

Stopping cold drafts is ALWAYS worth the effort!

[caberjim]

I am very intrigued by this - we have a wood stove as our sole heat source and while the house can be 76 degrees at waist level, the floor level is rather cold. Am I to gather that this would help?

Technical questions - our house is on piers, i assume the best thing to do is have the air intake come in from under the house. Where does it go to? right in front of the stove? under the stove? directly into the stove?

Metal piping? What size? 1 or 2 or 3?

adding - It is not an airtight stove (or an airtight house)

thanks

[logbuilder]

How the outside air kit works on each stove varies by make and model. But for my vermont castings stove, the kit is a small box that covers up the air intake on the bottom back of the stove. On that box is a 3" outlet. You cut a hole in the floor and then put a piece of 3" metal flexible pipe on the stove and then run it down the hole in the floor. This is how it works when you have a crawl space underneath. This causes the stove to draw all the fresh air needed from outside the house.

[cougkid]

Logbuilder, what would you do in my situation, where I have an unfinished basement beneath my woodstove? Would you draw air from the basement, or run the pipe all the way to the outside?

[logbuilder]

The flexible metal tubing is not expensive. Since one of the reasons for the kit is to not pull air from any space that is occupied and since it would seem reasonable that sometime in the future you might do something with your basement, I'd go ahead and route it to the outside.

[logbuilder]

BTW, the 3" metal flexible tubing you need is the same as that used to vent hot water heaters. When you go to the hardware store, refer to it as that. Otherwise you might just get a blank stare.

[cougkid]

OK, thanks for all of the tips. Cool house by the way. I grew up in Stanwood.

[Boleyz]

Fires need air for combustion and will draw that air right across the floor (Through the lowest crack...usually the entry door) if the fireplace is not vented.

Best solution I ever saw was a 1/2" black steel pipe punched through the fireplace, along the baseboard and then elbowed through the wall to the outside.

To keep critters and cold air from entering, a simple ball valve was in the line on the baseboard. To start a fire, the vent was opened first, and then the fire was lit and drew it's air through the pipe.

Simple solution...you can do it in an hour...most plumbing supply places have nipples long enough to do it, so you wouldn't even have to thread any pipe.

[seedspreader]

LOL, we just have nice 121 year old house that has cold air returns in the floor for the oil burner in the basement. All we heat with is our woodburner... it's airtight, the house isn't air tight by modern standards but well insulated with good windows.

I've never heard of air inlets in an old farm house. interesting.

ps... anyone with those outside air vents have pictures of your set up?

[fastbackpony]

OK - i'm going to just admit it . . . i've never heard of this

we have a new house - aug. 10 - 06 and are heating completely with wood - and we have no vents of any kind. did we do something wrong ? ? are we going to die of oxegen depletion in the middle of the night ? ?

sometimes it gets too warm and i crack a window.

i grew up in an old house, and we had a big basement with a big double barrel stove, and i never even heard of anyone mentioning venting in cold air for this.

whats the deal ? ? ? why would this be necessary ?

it stinks to be so dumb about these things . . . . . sorry

[agmantoo]

I realize the discussion is regarding combustion but I have seen buildings that were slightly positive pressurized to prevent inflow of hot or cold. A small amount of outside air was force fed into the return duct work to be conditioned then released into the living area. This practice eliminated the creature discomfort associated with cold drafts.

[Boleyz]

Originally Posted by fastbackpony

OK - i'm going to just admit it . . . i've never heard of this

we have a new house - aug. 10 - 06 and are heating completely with wood - and we have no vents of any kind. did we do something wrong ? ? are we going to die of oxegen depletion in the middle of the night ? ?

sometimes it gets too warm and i crack a window.

i grew up in an old house, and we had a big basement with a big double barrel stove, and i never even heard of anyone mentioning venting in cold air for this.

whats the deal ? ? ? why would this be necessary ?

it stinks to be so dumb about these things . . . . . sorry

There's not much danger of your woodstove depleting all of the oxygen in your home. A combustion air vent wouldn't hurt though.

The problem in the OP had to do with drafts and cold floors.

His wood stove SUCKS...literally...it is sucking air through the various cracks and crevices in his old house and therefore, there is a constant chilliness at floor level, as the outside air is drawn in and used for cumbustion by the fire.

Venting the fireplace to the outside is a means to provide air for cumbustion without sucking it across the room. Make the vent nearer the fire, and you eliminate the draft across the floor.

Your stove is sucking air as well, but many modern fireplaces are vented to the crawlspace...

ZYG asked for a picture...here's a diagram...Mobile Home Installation

[caberjim]

We have an older steel Country Flame woodstove. The air intake and dampers are on the front doors - big knobs that spin in and out. Is it worth it to run a pipe thru the floor that comes up right in front of the woodstove doors? That would bring fresh air up to the outside of the stove where the intake is.