Ask Our Experts

Answers to your questions about gardening, energy, homesteading and other sustainable living topics.

Add to My MSN

Woodstove Air Supply

10/8/2010 11:48:43 AM

Tags: energy savings, woodstoves

Should woodstoves and fireplaces have an outdoor air supply, or should they draw on indoor air? I've heard both.  

Back in the 1980s, I was one of those people who promoted outdoor combustion air, but that was before anyone had seriously studied the issue. Since then, testing done under controlled conditions has shown no advantage, and has revealed some disadvantages. Nevertheless, some jurisdictions require outdoor combustion air supplies. 

Three reasons are often given for supplying outdoor air: 

• To prevent the wood heater from “starving for air” in a tight house 

• To prevent depressurization of the dwelling that might affect other fuelburning devices  

• To save energy by not using warmed room air for combustion  

However, as several studies have demonstrated, none of these reasons stands up to scrutiny. 

The main issue is that the air consumption of a woodstove is only a small part of a much larger exchange of air between the house and the outdoors. The average air consumption of a modern wood heater is about 10 to 25 cubic feet per minute (cfm). Even a tightly sealed, 1,500-squarefoot home would have an absolute minimum air change rate of 66 cfm, and the rate for most houses would be far higher. 

On the question of saving energy, remember that there’s no free lunch. In other words, outdoor air will have to be heated one way or another, either by the fire, or by seeping in through leaks and being warmed by your space-heating system. Regardless, if your local building code requires an outdoor air supply, it must be installed. 

However, I have seen a few cases in which wind pressure around a house caused hot exhaust to be sucked back outside from the stove or fireplace through the combustion air duct. If your wood-heating appliance malfunctions in windy weather, disconnecting the outdoor air supply may fix the problem. 

John Gulland,  

Content Tools

Post a comment below.


Subscribe Today - Pay Now & Save 66% Off the Cover Price

First Name: *
Last Name: *
Address: *
City: *
State/Province: *
Zip/Postal Code:*
(* indicates a required item)
Canadian subs: 1 year, (includes postage & GST). Foreign subs: 1 year, . U.S. funds.
Canadian Subscribers - Click Here
Non US and Canadian Subscribers - Click Here

Lighten the Strain on the Earth and Your Budget

MOTHER EARTH NEWS is the guide to living — as one reader stated — “with little money and abundant happiness.” Every issue is an invaluable guide to leading a more sustainable life, covering ideas from fighting rising energy costs and protecting the environment to avoiding unnecessary spending on processed food. You’ll find tips for slashing heating bills; growing fresh, natural produce at home; and more. MOTHER EARTH NEWS helps you cut costs without sacrificing modern luxuries.

At MOTHER EARTH NEWS, we are dedicated to conserving our planet’s natural resources while helping you conserve your financial resources. That’s why we want you to save money and trees by subscribing through our earth-friendly automatic renewal savings plan. By paying with a credit card, you save an additional $5 and get 6 issues of MOTHER EARTH NEWS for only $12.00 (USA only).

You may also use the Bill Me option and pay $17.00 for 6 issues.