Compared to a 20 year old furnace how much does each design improvement increase AFUE:
Draft inducer fan Ignitor vs pilot Faster fan startup (is this due to the draft inducer) Hx design chages? Anything else?
Yes.
The biggest improvement, IMO, is the ignition vs. the standing pilot.
Second heat exchanger, Extracts so much heat from the exhaust that the water vapor in it condenses and runs out a drain (my condensate pump runs summer AND winter) The inducer fan is needed because the exhaust gases are too cool to rise up a chimney. Instead, they're pushed out through a 3" PVC pipe that barely gets warm. =20 (Been using a Carrier SX since 1994)
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Heatman,
But is it really cheaper to the consumer? I have a 25 year standing pilot that I have replaced the thermo-couple once. I have a 10 year old 80% that I have replaced the igniter on twice. I got off cheap because I know the part only cost $16. But the average Joe in this part of the country pays the HVAC man $75 for the part and a service call.
Plus you have to add in the cost of running the inducer fan and that igniter uses a good bit of electricity every time it glows. KWH are cheap here but what does it cost each time it glows where they cost more?
So who is coming out ahead here? Is the consumer really better off all costs considered?
Serious questions.
Colbyt
You may be right about the biggest improvement, but the improvement can't be much. My lowest gas bills in the summer are about $10 for heating water with a water heater has a pilot light. I doubt that the pilot accounts for more than 10 percent of the gas usage, so the pilot probably cost about $1 per month or $12 per year.
BTW, I elected to install a water heater with a pilot light and am glad that I did because operation is nearly silent. I would hate to listen to an inducer fan every time the water heater burns; the damn inducer fan on the furnace makes a lot of noise. More over, the pilot light means that you continue to have plenty of hot water during electrical outages. None of this applies to a furnace since you can't operate it without electricity and the burner makes as much or more noise than the inducer fan. But, it does go to suggest that the benefits of electrical ignition is minor.
So my 60% 20 year old furnace will achieve 80% by eliminating the pilot?
Why doesn't everyone just replace their pilots with an ignition system?
Doesn't quite add-up
I asked the HVAC tech who lives a few houses away about how much it costs to replace my pilot light with an ignition system. He said that his company charges $600 to do that. Presumably that's why it doesn't get done often. He said that they sometimes have to add new boards to make it work, etc. So I just shut mine off completely during the summer and parts of the spring and fall. It's easy enoug to re-light and I think it made a $5/month difference on my gas bill. I was using less than $5/month for gas all summer long. Not exactly scientific, but at these gas prices why not shut off the pilot whenever you can.
He's talking about the 80%, not the 92% stuff. The flue gases will rise up the chimney, but will condense real bad and rot out the chimney quick
Other than that, you're correct....
improvement
My Carrier POS has been in for 10 plus years and I haven't had to do anything to it except for filters. What brand is it?
The efficiency rating is the annual rating. If you blew out your pilot every year and didn't have to replace it, you'd gain a couple of efficiency points.
See my first post.
BTW, that Carrier POS is a 2 pipe, one intake and one exhaust. That may have something to do with the longevity of the ignitor.
My summer gas bill would be non-existant if it weren't for the gas stovetop. I use a de-superheater for hot water during the summer. It gets so hot I had to install a tempering valve on the discharge.
I couldn't agree more. I did get lucky because no one in the house can hear the inducer on my Carrier POS. There is a direct vent WH that I'm looking at when my current one goes out. It get combustion air from the outside as well as vent the flue gases out. I will not be getting a tankless.
I get that call from time to time. "I don't have any heat, but I am supposed to have gas! Why isn't it working?" 'Your furnace has to have electricity to operate the controls and the blower.' "Oh."
improvement
It's also the amount of gas being burned and used to warm up the house. The ofrices are smaller and the HX is more efficient.
Second heat exchanger, Extracts so much heat from the exhaust that the water vapor in it condenses and runs out a drain (my condensate pump runs summer AND winter) The inducer fan is needed because the exhaust gases are too cool to rise up a chimney. Instead, they're pushed out through a 3" PVC pipe that barely gets warm. (Been using a Carrier SX since 1994)
Except what you are talking about isnt a 80% unit..its a 90% or better.
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