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Before You Shop
Before you make changes to your heating system, find out if there are any simple, cost-effective steps you can take to get the most out of your investment. Buying a heating system means dealing with contractors. The more information you have, the better equipped you will be to hire someone who will know how to size and install the system properly.
Sizing Up Contractors
Choosing the right contractor may be harder than choosing the right heating system. A competent heating contractor will determine your heating requirements (or heating load) after checking a whole list of factors—no rule of thumb here. The list includes the size and style of your house, how well insulated and airtight it is, how much useful solar energy comes in through the windows, how much heat the lights and appliances give off, the supplemental heat supply if any, the condition of the ducts or pipes, the typical thermostat setting, and the number of occupants.
In fact, the contractor should ask you a lot of questions. Are there any drafty areas? Any moisture problems? Hot or cold rooms? What changes are you about to make? He or she should also ask to review your past utility bills. All of this information will indicate how much heat the heating system must generate on the coldest days in your climate and over the annual heating season in order to keep you comfortable. These numbers are usually expressed in Btu (British thermal units) per hour, and per heating season.
To get the most reliable estimate, hire someone who will test your house with a blower door. This may not be a heating contractor, but a "house doctor," or home performance contractor. Using a blower door and other diagnostic tools, he or she can tell you exactly how and where your house leaks air—and how to reduce the leakage. If you have a forced-air system, a test using a blower door and a duct leakage tester will identify leaky ducts. A complete evaluation includes all the items mentioned above.
With this information you can decide which improvements are worth making before choosing a new heating system. Follow-up tests after improvements have been made will then give you a more accurate estimate (generally lower) of the size heating system your home needs.
It goes without saying that heating equipment should be installed properly. Yet bad installation accounts for the loss of 30% to 50% of the heat in many homes. Before you decide to buy, obtain firm, written bids from several companies on both the cost of upgrading existing equipment and the cost of buying and installing a complete new unit along with any other fittings and adjustments required. These estimates should include changes to the ductwork or piping and a final balancing of the heat supply to the house. Remember that you are investing for the long term. It may cost more to have everything done right. The contractor who offers the lowest bid may not spend the time it takes to do a good job.
If you are upgrading a forced-air system, be sure to have the ducts sealed first; if you are having a new system installed, demand tight ducts. A mastic sealant—never duct tape—should be used to seal all joints and connections.
After all the work is completed, your contractor should perform a steady-state efficiency test if you have a combustion system. On a forced-air system, ducts should be checked for leakage and the distribution system should be balanced (see chapter 4: Air Sealing). If you had insulation added and air infiltration holes sealed, a new air leakage test should be done with a blower door, and, in some cases, a worst-case depressurization test should be done to make sure there won't be any backdrafting of combustion appliances. Compare the results with the original tests run to be sure that all the improvements were made, that no new problems were introduced during installation, and that your new system is operating at top efficiency.
Trethewey, Richard with Don Best. "This Old House: Heating, Ventilation, and Air Conditioning". Boston: Little, Brown and Company, 1994.
Wilson, Alex and John Morrill. "Consumer Guide to Home Energy Savings". Washington, DC: American Council for an Energy-Efficient Economy, 1996.
Excerpted with permission from No-Regrets Remodeling by Home Energy (1997)