Dear Angie: How do you determine the right size furnace? Should I do a home energy audit first?
— Kate W., Lansdale, Penn.
Dear Kate: Figuring the right furnace fit comes down to what's known as a Manual J load calculation. This gives heating and cooling professionals the exact furnace size in British thermal units (BTU) per hour.
A Manual J calculation takes into account the size of your home and its ductwork, as well as overall energy efficiency. That's why an energy audit is a good idea. Audits start at about $250 and are available through many HVAC companies as well as companies that specialize in energy efficiency auditing. Steps you take to boost efficiency, such as adding insulation or replacing windows, will affect the load calculation.
Seems like a lot of fuss over having enough hot air, right? But installing a system that's too big or too small has consequences for your comfort and costs.
A too-large system won't cycle correctly. It will heat the home too quickly, then shut off and repeat the process more often than necessary. A system that's not big enough will run longer than it should to reach the desired temperature. Either way, an improperly sized furnace means wasted energy and overworked equipment.
Service providers recommend replacing furnace, air pump or air conditioners that are at least 10 years old and starting to have problems. Ideally, your HVAC system's major components are the same age, or close to the same age, so they can be replaced at the same time. That allows your HVAC company to easily install compatible units and offer a package discount.
The average cost of a new HVAC system is around $10,000, but prices can vary widely, depending on the brand and type of equipment and size of your home. Your cost will also depend on whether you add services, such as weatherproofing or new ductwork.
Angie Hicks compiles the best advice from the most highly rated service pros on Angieslist.com to answer your questions. Ask Angie your question at firstname.lastname@example.org.
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