combustion air

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Can Atmospheric Combustion Work in a Spray-Foam-Insulated Attic?

In an attempt to reduce costs, some contractors do questionable retrofits on attic furnaces

Posted on Mar 11 2015 by Allison A. Bailes III, PhD

A while back I wrote about the incompatibility of putting an atmospheric combustion furnace in a sealed attic. Most often the attic is sealed by installing spray foam insulation at the roofline, thus bringing the attic inside the building enclosure and turning it into conditioned spaceInsulated, air-sealed part of a building that is actively heated and/or cooled for occupant comfort. (directly or indirectly). The good news is that some installers understand this problem and seek to address it. The bad news is what a few of them do.

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Image Credits:

  1. Unless otherwise noted, all photos are by Energy Vanguard

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Providing Outdoor Combustion Air for a Wood Stove

We brought ducted outdoor combustion air to our wood stove by punching a hole through the back of the unused fireplace

Posted on Oct 14 2013 by Chris West

In November 2012, I started on a deep energy retrofit of my 1976 raised ranch in northwestern Vermont, in the shadow of Mount Mansfield. As a Passive HouseA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. consultant, I wanted to make my leaky (8.25 ach50) house with fiberglass-filled 2x4 walls and a tuck-under garage much more energy-efficient.

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Image Credits:

  1. Chris West

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Sealed-Combustion Appliances and Hot Tub Parties

In a tight house, combustion appliances and exhaust fans are all fighting over a limited supply of indoor air

Posted on Aug 5 2013 by Erik North

Sealed-combustion appliances are apt to become more common as the new energy codes introduce residential airtightness standards. This means that you’ll need to pay close attention to heating system safety. Fortunately, the new codes lay out explicit guidelines for combustion appliances.

Building and energy codes often get adopted piecemeal around the country. In Maine, we’ve adopted the 2009 International Energy Conservation Code (IECC International Energy Conservation Code.), but have exempted towns below a certain population level.

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Image Credits:

  1. Will Perkins

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How to Provide Makeup Air for a Wood Stove

Should your wood stove get ducted outdoor combustion air direct to the firebox, or to a location near the stove — or perhaps no ducted outdoor air at all?

Posted on Dec 19 2011 by Scott Gibson

Wood stoves used to be pretty uncomplicated devices. Even though they weren’t airtight and they weren’t especially efficient, these cast-iron stoves warmed plenty of New England farmhouses in the dead of winter.

Our forebears never considered the source of makeup air to replace all the heated combustion gases that were going up the flue. They didn’t need to, because back then, houses were leaky. As the stove burned its load of oak or maple, makeup air had no trouble finding its way into the house.

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Image Credits:

  1. Justin Fink/Fine Homebuilding magazine

Green Basement Renovation: Adding Under a Home

Bridgewater, CT

Jan 28 2009 By Rob Wotzak | 2 comments

General Specs

Location: Bridgewater, CT

Space affected: About 2/3 of a 900-sq.ft. basement
Remodeling contractor: Andy Engel
Completed: Summer 2004

General Design and construction

  • Remodeling existing space with simple details keeps the project's actual and environmental footprint small

Building Envelope

  • Relatively dry basement - no drainage system required
  • Continuous, vapor-permeable insulation (EPS) on floor and walls
  • Thorough air-sealing (spray-foam and seam tape)


  • New fresh air supply ducts for existing boiler and water heater
  • Backdraft dampers in fresh air ducts

Interior Finishes

  • Glue down cork flooring


  • Owners run a dehumidifier to maintain a comfortable and healthy relative humidity

A layer of rigid insulation covers cold concrete and makes a warm and inviting new room.

When the owners of this home in Bridgewater, Connecticut called in contractor Andy Engel to convert a portion of their basement into a rec room, they weren’t sure how far he would need to go to make it comfortable and healthy. Fortunately for them, there was no evidence of water problems, so Andy was able to do all of his moisture, air, and, heat control details within the existing basement.

Lessons Learned

There’s always an easier, better, less costly way
Andy was able to avoid fastening through the insulation into the concrete walls, but felt that he needed to screw the subfloor to the slab to get a solid base for the new floor. He says he would have done things differently if he had more information at the time. “Instead, I'd have used a leveling compound and done a true floating floor. I just recently learned that's approved by the Wood Flooring Manufacturers Association.”

The steps Andy took are mainly common-sense ones aimed at long-term durability and economy, two goals that happen to go hand in hand with the green movement. So, you might say that Yankee frugality is a good quality to have for when renovating sustainably.

— Rob Wotzak is Associate Editor at

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Image Credits:

  1. Charles Bickford/Fine Homebuilding

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