View Full Version : Replace my 15yr old furnace …why... just because???

04-16-2007, 05:06 PM
Presently installed:
House is 1900 sq feet.
Yearly Outside Temps: winters are -25c to +5c for 5 months, summers are +20c to +30c for 3 months.

A/C is a Lennox model c18-21qc-1, ser 6390f32698, built 06/1990

Furnace is a Heil model cugi075ad01 ser l914939042, installed mar 1992, Input 75,000 Output 57,000 ( N’gas, has a pilot light and shares vent with N'Gas water heater ).

The last couple of visits for maintenance the service guy suggested replacing the ~15 year old furnace might be in order. No cracked exchanger or anything but lots of rust. I have several CO2 detectors in the house ... never a problem reported by them. The furnace & A/C unit have only needed service 3-4 times in the 10 years I have been in this house.

My understanding is that the new mid-E furnaces won’t really save me much more in fuel. The high-E will, but are more expensive and will require side venting and not the shared vent I have now.

Any opinions as to whether I should replace one, or both, or neither of these units???



04-16-2007, 06:05 PM
Here is a PIC of it running ..... seems to be more "yellow" than i would expect.



04-16-2007, 08:08 PM
A new high-efficiency furnace is in the order of 25% more efficient than yours. The new a/c units could be twice as efficient, but it seems you may not use it that much. They will also use a different refrigerant. The sealed combustion furnaces are much quieter, if that is a factor. Side venting has its advantages. Guess where all of the air that goes up the flue come from? Inside of the house. Guess where the makeup air comes from - through cracks and leaks in the house. So, by using air from outside, you have less cold air to heat, and gain additional efficiency.

One of the nicest features of some of the new furnaces, is the option of a variable speed fan. This does add to the cost, but makes comfort levels better, and a/c operation more efficient, too. They start our slowly, so you don't hear it while moving the cool air in the ducts slowly until the heat exchanger gets a chance to heat up, then ramp up the speed. If it is mild, they may never get to full speed. same with the a/c. Because the air is moving over the cooling coils slowly, it pulls more humidity out of the air on each pass. You can often be much more comfortable at a higher temperature if the air is drier. My guess is that you don't run yours too much because it just gets cold and clammy unless it is fairly warm out. A variable speed fan means that on those mild, but clammy days, it will still run long enough to dry the air...a much valued feature where I live.

Will it ever pay back in energy efficiency? Probably not. But, I will say, my old system was about the same efficiency as yours, and my a/c electric bill use went down $50/month in the summer. Heating went down around $30/month. It's harder to tell, since there have been some significant rate hikes, but my bills have remained fairly constant.

I switched from a furnace to a boiler, and the new one I had installed this January was eligible for a $1100 rebate from the utility company. Don't know if any Canadian utility companies run similar promotions.