How to Determine Proper Furnace Size

Residential gas furnaces are available in several of sizes and are measured in British thermal units, or BTUs, per hour. A BTU is equal to the amount of energy that is required heat or to cool 1 pound of water. It’s possible to use very basic calculations to get a rough estimate of furnace dimensions, but it’s important to get an HVAC specialist or other qualified specialist perform thorough load calculations to determine an appropriate furnace size and type for your residence and heating objectives.

Calculate the square footage in the living space of your home. Measure the length and width of every room and multiply those two numbers. Add of the room dimensions together to get the square footage. Don’t include dimensions for rooms which don’t possess vents or the ductwork for heating or ac. Measurements for rooms that you don’t plan to heat or cool, such as garages, workshops, covered patios or sunrooms. Quantify your ceiling height with reference; lots of sizing charts assume 8-foot ceilings, and you might have to adjust your calculations for taller ceilings.

Think about the weather, such as low and high temperatures, and also the duration of every season. According to U.S. Department of Agriculture plant hardiness classifications, San Francisco is in Zone 7. Even though you generally have hot summers and mild, cool winters, the weather is too cool to be eligible as a region having a year-round hot climate. San Francisco residents need a little to midsize furnace, and encounter of the seasons. Generally, the colder the weather, the bigger the furnace.

Consult with a furnace manufacturer or installer and observe recommended graphs to find out the best furnace dimensions for your home. The exact same USDA zone classifications aren’t always followed by installers. By way of example, if you pick a model using a 95-percent annual fuel use efficiency and your house has between 810 and 1,350 square feet, then you want a 40,000 BTU per hour furnace. In case your home measures between 2,035 and 2,070 square feet, a 80,000 BTU per hour unit is best, and more than 3,390 square feet requires a 120,000 BTU per hour furnace.

Prior to selecting a furnace consult an HVAC specialist for evaluation and load calculations. Manufacturer recommendation graphs give you an easy starting point, however there are lots of other important criteria to consider, such as the age and construction of your house, how much insulation is in the walls and attic, and the quality of your windows, doors and seals. Homes with adequate insulation, energy-efficient windows and proper sealants around windows and doors experience less heat loss than those without.

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