Q. I had my house built 30 years ago and installed a gas boiler, approximately 83% efficient that heats my hot water also. There are a couple of gas appliances such as a dryer and range in the house. We have three bathrooms in the house, and each has a bath fan. Recently I installed a higher CFM range hood and I’m concerned that I have enough air supply into my home. There is a wood fireplace that has an outside air inlet. Do you think I need more make up air? — Jim of Angola
A.The building sciences of operations of a home are not simple especially when you start considering anything specialized.
Regarding heating, cooling and air handling systems, there are several factors including how many people are in your house including pets. How many air changes does your house currently have? This can be figured with a Blower Door test where they temporarily install a door curtain with a controlled blower mounted in it. Testing the resistance will produce your house performance results.
Most of the time this leads to addressing air leakage problems by caulking or sealing.
Assuming your home was built to be well-insulated and airtight, make up air is probably needed. When you use air for combustion such as gas dryer, gas range and gas boiler, they all need air to operate properly. The air quality in the baths to prevent mold and mildew is prevented by using the bath fans. All these require air.
Then you turn on the large range hood and it’s likely the fireplace will puff smoke back into the home as your home tries to equalize the air pressure.
A number of air ventilators are available to solve these problems. They can gently move air into your home through an outside duct run through the crawl space or basement and distributed into your house through duct work. Some have sophisticated controls, and heat exchangers and some are simple by turning on when pressure needs to be equalized.