Sizing Your New Furnace

Sizing your new furnace does not pertain to the actual dimensions of the system, but rather the system’s heating capacity. You want a system that can adequately heat your home, while not costing you too much in fuel or energy costs each month. You’ll want to look at the system’s Annual Fuel Utilization Efficiency (AFUE), which tells you how much of the fuel will be translated into usable heat. If the system you’re looking at has a 90 percent AFUE rating, then that means 90 percent of the fuel will be turned into heat, with the remaining 10 percent being exhaust. It’s important to keep in mind, however, that you can only compare the AFUE of the same type of furnaces, such as one gas furnace to another.

A furnace that’s too large for your home can result in it cycling on and off too much, since it’s generating more heat than your home needs. This can result in a lack of heating efficiency, not to mention mechanical problems that can severely shorten the system’s lifespan. With a system that’s too small, meaning it can’t produce enough heat to keep the house warm, it can run too long and too often, resulting in higher energy costs and home that’s not comfortable during the colder days of the year.

Heating Capacity

Your new furnace’s heating capacity will be shown in British Thermal Units, or BTUs. You’ll want to be sure that your new system can produce enough BTUs to keep your home at a comfortable temperature. The number shown on the certificate on the new model will tell you how many BTUs per hour the furnace will produce. You’ll need to know your home’s square footage in order to determine what your new system’s heating capacity should be. If you need 80,000 BTUs per hour to heat your home, then you won’t want to install a furnace that only produces 60,000 BTUs per hour. You also need to take efficiency into account, because if the system shows 100,000 BTUs per hour, but is only 90 percent efficient, it will only produce 90,000 BTUs per hour.

Manual J Load

While BTUs are very important, it’s also essential to take your home’s manual J load into consideration before installing a new furnace. The manual J load refers to how your home is built, what type of insulation and windows you have, and how much sunlight the house receives on a daily basis. All of these factors play a part in heat loss and heat retention, and our HVAC technicians know how to calculate your property’s manual J load. When sizing your new furnace, we’ll take everything into account so that you end up with the best system possible.