What Size Furnace is Right for My Home?
When deciding on the size of the furnace, the size of your house is one factor to consider, but it is not the only factor. As a rule of thumb, 25 to 30 BTU’s per square foot should be sufficient in mild climate. If you live in a colder region, count on 40 BTU’s per square foot.
This said, take a look at what you have now, assuming your current home is already being lived in. If you are happy with the performance of your furnace, i.e. you are kept warm while not suffering from overly costly bills, and your only complaint is that the unit needs to be replaced, then get the same size again. There is no point in re-inventing the wheel.
What you are really interested in is the efficiency of the furnace, not the size. For instance, you invite problems with a unit that under-performs. Obviously, you will have trouble staying warm, but in addition, the unit will wear out more quickly because of the continuous struggle to reach the desired temperature. So, trying to save money with a modestly sized furnace is not a long-term solution. Eventually it will actually turn out to be more costly.
Some people have the misconception that an oversize furnace will save money because it is so powerful that it reaches and maintains a certain temperature more easily. It is true that a large furnace will get your house warm quicker, but it does so with an unnecessary output of energy that is really geared toward much larger rooms. In this way, energy is squandered and you end up paying more in your monthly bill.
If you don’t believe the furnace you currently have suits your needs, a professional heating expert will be able to tell you what exactly what is going on. You might, for instance, have an insulation problem you are not aware of. Caulking and weatherstripping might take care of those issues without your even needing a new furnace. Or your thermostat might need replacing. In some cases, an attic’s insulation might be failing, or perhaps was never even installed. Either way, before replacing a furnace the house needs to be inspected to ensure that the furnace is operating under conditions that allow for optimum functioning.