A.Richard Karg responds: Yes, an oversized heating system is wasteful for three reasons: 1) It reduces the annual efficiency of combustion heating systems; 2) it increases the potential for flue condensation in mid-efficiency systems; and 3) it increases the cost of heating systems.
Now for some explanation. First, an oversized combustion heating system will not fire as much as a system that is sized properly. Instead, it will "stand by" more and lose more heat up the flue. The more oversized it is, the greater the stand-by time, and the higher the fuel bill.
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