When you're in the market for a new furnace, of course you want to think about more than just the cost. The overall heating ability of your furnace will affect your comfort during winter while also protecting your home from damage due to cold weather and frost that can literally build up around windows and elsewhere. While a powerful furnace is important, it's also good to think of energy efficiency and not pay for a larger furnace than what you need. Note a few tips when you're ready to shop.
BTU versus AFUE rating
The BTU rating of a furnace refers to British Thermal Units, or how much heat a furnace can produce. Most residential furnaces average 40,000 to 100,000 BTUs for furnaces; the furnace manufacturer will tell you the recommended size based on your home's footprint. However, you'll want to invest in a larger size if your home is especially drafty or if you live in an area with harsh winters, as the furnace will need to work harder in these cases. If your home is very well insulated and you've recently invested in weather-stripping for the windows and have energy efficient windows as well, you can typically go down a size for your furnace.
The AFUE rating or annual fuel usage efficiency is different than the BTUs; this tells you how much energy the furnace uses to operate the heating element, versus energy used for other parts of the furnace. A furnace with a higher AFUE rating will use more of its electricity to create heat; one with a lower rating will use more electricity to run the blower, belts, and other such pieces. Note that a higher AFUE rating doesn't mean that the furnace will necessarily use less electricity overall, but the electricity it does use will be used efficiently, creating heat for your home and not just powering other parts of the furnace.
Maintenance
Note the filters that are recommended for the furnace and how often they should be changed, and if they can be swapped out easily, depending on where they're located. Can you easily access the front panel and, if so, reach the belts inside so you can clean and oil them? For a gas furnace, is the pilot light protected by surrounding walls so it's less likely to go out, and can you reach it easily if it should go out so you can relight it? These small features can actually go a long way toward allowing you to maintain your own furnace, keeping it running efficiently and saving you the cost of repairs.
