Spray Foam Attic Gas Furnace

Earlier this year i got a question about a home that had spray foam insulation in the attic.

Spray foam attic gas furnace.

Sealed combustion appliances fueled with natural gas cost less to operate than electric ones. Air tight homes require sealed combustion hvac appliances and mechanical ventilation. Let s say you bring the attic inside the building enclosure by putting spray foam insulation at the roofline the case with the two furnaces in my previous article on this topic. Now let s put some numbers to it.

These allow the furnace to use air from your home for the combustion process. If a high efficiency unit can hit 90 with a typical installation then you can achieve a rating of at least 65 with a standard installation. The good news is that some installers understand this problem and seek to address. My plan was to get a high efficiency gas fired furnace in lieu of a heat pump or electric furnace.

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 space directly or indirectly. 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 space directly or indirectly. A lot of builders and homeowners are going with spray foam insulation because of the airtightness benefits but then the questioner mentioned that the spray foam contractor had intentionally left big holes to the outside by not sealing the gable vents.

The attic is a sealed space by polyurethane foam and will need a combustion air source. A furnace in the attic is a design that works for all homes. When you can use natural gas over electricity there is an opportunity to boost the efficiency rate of your furnace as well. Yes we re going to do math but it s just simple arithmetic.

Spray polyurethane foam insulation can achieve air tightness of 0 10 to 0 20 air changes per hour. The spray foam contractor installs louvered grilles between your attic and your living space. Note that this isn t a good idea if you have a very airtight high performance home or if your home simply isn t large enough to provide the air needed for combustion.