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Sharing my search for a replacement furnace may save you some steps or answer some questions for you.

Older, 5 years or more furnaces are typically over sized for the house they are put in. Gas was cheaper then. This causes the furnace to run more often. A quick heat up and a more frequent duty cycle. The furnaces typically have 3 large flues in them, connected at the top by a horizontal pipe. Heat that is not used goes up the chimney; your chimney pipe gets very hot.

A bungalow of 1300 square feet needs about 50,000 BTU to supply comfortable heat to the building. The installations described above typically have 150,000 and above for a BTU output for the furnace. That means ¾ of the heat is going up the chimney!

Furnace manufactures manufacture on different scales one may be 20 –40-60-80-100-120-140 etc while the next may run 30-50-70-90 etc. Different brands will put you closer to your actual needs.

Comfortable heat often has more to do with furniture placement than furnaces. The heat will be sucked out of the heat vent by the air return. It will get there by the most direct route. If you have a chesterfield in front of your air return, your room will seem cold. More air returns in more rooms is a better plan and, try not to block them with furniture.

Furnace shopping is a hum! There are choices to be made as much to fit your budget as to heat your home.

The older over rated furnace will probably be pulling 40 or 50% efficiency in heating although it is rated at 50 to 70% in burning efficiency. (Because of oversize waste)

There are flavors of high efficiency furnaces to be high efficient rated they have to be over 78% burning as legislated in the US. Most popular is the 80% models. Popular, because of a couple of reasons. People are suspicious of the service life and maintenance costs and down time of the 94% etc furnaces. Also, the cost is prohibitive easily going 1000 dollars higher than the 80%.

What is similar in them all is the gas burning. They have automatic low and high settings for the amount of gas that goes into the burners. They are smart enough to figure out which one you need. The down side, these super systems are designed for a continuous run motor. The art of the system is in the electronics which matches the high/low burn to the motor speed. If you plan on shutting your heat down and don’t have the air condition installed, best to pass it up!

On 80% and above you are given choices between the standard but newer capacitor start motors and the variable speed motor which is certainly a sweet motor. The capacitor start is what you are used to in your furnace. A low speed and a high speed available. They typically use a high of 4.5 amps running on high (500 watts/hr)

The new “DC” Variable speed motor can slow down to move less air than a bathroom fan and go higher in speed than your capacitor motor. If you compared two motors in service running 24 hours a day all the time, the DC motor would be cheaper, your house would be more comfortable and your humidity always correct. There are no real numbers out on power consumption. One manufacturer says 373 watts but doesn’t say if that is per hour, day or week and they won’t give any more information. Because of continuous run system and all the publications say they are cheaper I would make that per day. Hardly planning material!

To run the capacitor motor all the time is going to cost about 265..00 per year for electricity. That would be 4390 kw/h. The DC motor will cost about 223.00 per year for electricity. (Based on .06 per kw/h at 3270 kw/h)

The cost of the DC motor in these furnaces will be 600.00 + up charge for the furnace above the capacitor motor. It will take you 30 years to make up the difference in price of the motors running continually, as if that is going to happen.

It is not possible to retrofit a DC motor into a capacitor furance of any year. Gotta live with what you choose!

My choice after I drove every one nuts?

I went 80% high efficiency half the size of the furnace I now have (2 flame levels) and a capacitor motor..