 | Howard McDaniel is president and owner of Even-Temp of Wichita, Inc... Howard started Even-Temp of Wichita, Inc. in 1991. Even-Temp is a fully-licensed and bonded residential and commercial mechanical contractor in Wichita and the surrounding areas. Howard has been a member of the Kansas Cooling Contractors Association (aka K.C.C.A.) since 2001. He is also a member of the B.B.B. and Chamber of Commerce. Howard’s education includes graduate of Pittsburg vocational technical college and 5 years of schooling through the Local 171 Plumbing apprenticeship school. Howard built Even-Temp to what it is today. He started his business working many hours, night and day, by himself to a successful business with over 20 employees. Howard is an honest, fair and considerate business man, which is proven by the number of customers he has and by the number of them that have been with him for over 10 years. Howard can be contacted at his office at (316) 262-2277, fax at (316) 262-5366, or you can e-mail him at Howard@eventemp.com. |
Home Improvement
2008-01-01 14:23:00
Sizing a furnace
How does one determine the correct size and type of furnace for a home?
One of the two most important aspects in your selection of a heating system is proper sizing. The other of course is type. We will talk about that at another time.
A properly sized heating system will provide a high level of comfort, while maintaining maximum efficiency. An oversized system will “short-cycle”, meaning that it will cycle on and off more frequently. Short cycling will limit your comfort due to the frequent on/off cycling and reduce the system operating life. Having said all of this keep in mind that with gas furnaces you don’t have to nail your requirement down to the very last BTU. Furnaces are typically sold in 20,000-25,000 Btu increments because the manufacturers know that with heating, you just need to be in ballpark in terms of how many Btu’s your home needs.
If you are off by even as much as 20-25%, there is no real harm. A good rule of thumb is that if your heating requirement is about 10% or more above a given furnace’s capacity, go up to the next size furnace. So how do you select the proper system size for your home? Here are some options:
1. Have a contractor visit your home and provide an evaluation of the sizing needed. An experienced contractor in your area may be familiar with your home’s floor plan and already know the size needed based on previous evaluations and installations. Unfortunately, contractors will not always agree on the proper size for your home. If not, ask them what criteria they used in their evaluation. If they are using only square footage in the evaluation there is absolutely no assurance that the recommended system will function properly. Studies conducted by heating industry trade groups have repeatedly shown that over 50% of the furnaces sold in this country are dramatically oversized. By “dramatically oversized” we mean furnaces that produce up to twice the Btu’s actually required. Our industry is trying to correct this problem through training programs that emphasize proper sizing procedures.
2. If you are replacing an existing furnace within your home, locate the Btu capacity of your existing furnace by removing the top front service panel from the furnace. Usually, the “Btu input rating” and “Btu output rating” are listed on the nomenclature plate on the furnace behind the service door. Most older furnaces are 80% efficient so the output rating will be 80% of the input rating. For example if the rated input is 100,000 Btu, the output will be 80% of this figure, or 80,000 Btu’s. Next, measure the square footage of the heated area of your home. In warmer climates it should be roughly 25-30 Btu’s per square foot. In colder climates it should be around 40 Btu’s/sq. ft. and in the coldest climates around 45 Btu’s/sq. ft.
If used properly, this method will provide the existing furnace sizing. Assuming it was sized properly to begin with the same size replacement system is a fairly safe bet. This method is more reliable if you have lived in your home for at least one or two heating seasons and have experienced the system performance first-hand.
3. Use a system size selector. This selector uses square footage and your climate zone to estimate the approximate sizing for your home. It is not scientific as it assumes all homes in each zone are approximately similar in construction type and insulation values. Don’t be afraid to ask questions and expect well thought out answers. Use your judgment when determining who really seems the most interested in providing you with straight-forward, valuable information.
