New furnace required - advice welcomed
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The tech told me the chimney can be up to 1" larger in diameter than the water-heater pipe.
In my case, 3" to 5" is no good, so a 4" liner will be required.
CVT vs. conventional automatic.
All new furnaces have ECM blower motors. The base level will have a constant torque motor with at least 5 speeds and the higher end units have full variable speed blowers.
After going through a lot of options I settled on a two-stage Carrier. Take a look at two-stage units. I think this is where the best value is. The more advanced modular systems look good, too, but they are often quite complex.
Another thing to consider now is shortages. I have been waiting for my Carrier units for a few weeks.
Here's some real-world data-
I replaced the 15 year old Heil POS split-system heat pump (complete with POS zone damper system) in my mother's house in January 2021. This was what the builder put in, completely undersized and a horrible install/choice. The development is 100% electric. My mother wants it to be 75 degrees+ in the winter. This system was worn out and couldn't heat past 67 on days where it was below 40 degrees outside.
I had a Daikin VRV-S light commercial multi-port system installed with two air handlers; one for downstairs and one for the teenage suite upstairs. The single condensing unit serves both. Each floor has it's own 'system' and thermostat. This was not cheap, about $17k including demo of the old, some minor ductwork, all new refrigerant piping and intercepting the 60 amp strip heater circuit to power the new condensing unit.
This was installed with a commercial crew from a well-respected residential/light commercial HVAC company and works flawlessly.
Her power bills were reduced by 50%, while heating her house 8+ degrees warmer than the previous system could. There is no strip heat and it will provide 105 degree discharge air at 28 degrees ambient.
I'm an HVAC designer by trade, 28+ years experience and kind of have a little knowledge about all this and I'm a little picky when it comes to this stuff. I can't be happier and I can't be more proud of the system I specified. I priced this with 4 companies, two were heavy residential/light commercial and two were commercial/industrial only. All of them had questions, weren't 100% on board and leery of the whole thing. In the end, the installing contractor was blown away by it all and impressed by it all. Daikin factory reps were even involved and I even paid for factory start-up.
I also had un-solicited quotes submitted in addition to quotes for the Daikin system that were "basic" residential split system heat pumps from Carrier/Bryant/etc. These ranged from $12-13,200 for basic, bang-on, bang-off systems. No thanks. The $4000 difference between basic crap and top-of-the-line system is amortized in less than THREE YEARS.
Bite the bullet.
I replaced the 15 year old Heil POS split-system heat pump (complete with POS zone damper system) in my mother's house in January 2021. This was what the builder put in, completely undersized and a horrible install/choice. The development is 100% electric. My mother wants it to be 75 degrees+ in the winter. This system was worn out and couldn't heat past 67 on days where it was below 40 degrees outside.
I had a Daikin VRV-S light commercial multi-port system installed with two air handlers; one for downstairs and one for the teenage suite upstairs. The single condensing unit serves both. Each floor has it's own 'system' and thermostat. This was not cheap, about $17k including demo of the old, some minor ductwork, all new refrigerant piping and intercepting the 60 amp strip heater circuit to power the new condensing unit.
This was installed with a commercial crew from a well-respected residential/light commercial HVAC company and works flawlessly.
Her power bills were reduced by 50%, while heating her house 8+ degrees warmer than the previous system could. There is no strip heat and it will provide 105 degree discharge air at 28 degrees ambient.
I'm an HVAC designer by trade, 28+ years experience and kind of have a little knowledge about all this and I'm a little picky when it comes to this stuff. I can't be happier and I can't be more proud of the system I specified. I priced this with 4 companies, two were heavy residential/light commercial and two were commercial/industrial only. All of them had questions, weren't 100% on board and leery of the whole thing. In the end, the installing contractor was blown away by it all and impressed by it all. Daikin factory reps were even involved and I even paid for factory start-up.
I also had un-solicited quotes submitted in addition to quotes for the Daikin system that were "basic" residential split system heat pumps from Carrier/Bryant/etc. These ranged from $12-13,200 for basic, bang-on, bang-off systems. No thanks. The $4000 difference between basic crap and top-of-the-line system is amortized in less than THREE YEARS.
Bite the bullet.
Also - Here is the sequence of operations for a "multi-stage gas valve" gas furnace-
Call for heat
Fire burner 100%
Fire furnace/evap fan
Run fan/burner at 100% for a minimum TIME (5 minutes?)
If setpoint not satisfied, continue at 100% unless temperate within ____ degrees of setpoint
My problem with this is most furnace burners are grossly oversized for homes in the southeast. Firing at 100% for 5 minutes will reach the setpoint 95% of the time, resulting in the gas valve and blower speed never seeing a reduction. This means your multi-stage gas valve is never utilized.
This is my experience.....
I will never again buy a gas furnace and I'm a big fan of gas.
Call for heat
Fire burner 100%
Fire furnace/evap fan
Run fan/burner at 100% for a minimum TIME (5 minutes?)
If setpoint not satisfied, continue at 100% unless temperate within ____ degrees of setpoint
My problem with this is most furnace burners are grossly oversized for homes in the southeast. Firing at 100% for 5 minutes will reach the setpoint 95% of the time, resulting in the gas valve and blower speed never seeing a reduction. This means your multi-stage gas valve is never utilized.
This is my experience.....
I will never again buy a gas furnace and I'm a big fan of gas.
That entirely depends on how the thermostat is set up. I would think that most properly configured thermostats would start on the low stage, and only switch to the high stage when it is taking too long for the temperature to rise.
Now if some dipstick got the W1 and W2 terminals swapped around...then it would do exactly as you described.
No, it's how the system is designed to operate from the factory. The thermostat has nothing to do with it.
Then how, pray tell, does the system know to "continue at 100% unless temperate within ____ degrees of setpoint" ???
Just put a new power vented hot water tank in and cap off the chimney pretty much the same price as putting a liner in the chimney.
It's pre-programmed into the control sequence from the factory on these multi-stage gas valve furnaces.
It sounds to me like someone didn't set up the multi-stage gas furnace for a multi-stage thermostat.
In any case, that's not how they work, if it's going to high stage first, it's either broken or set up wrong.
And, unless the furnace is connected to a communicating thermostat, it's control board has no idea what the setpoint is.
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I tell ya what - since you seem to know so much about this, why don't you help me figure out if it is indeed incorrectly installed.
I'll get more info and pictures. For now, it's a 92% AFUE furnace, I believe it has a modulating gas valve (maybe it's 2-stage), 2-speed evap fan motor. Lennox, made in 2015, installed in October 2015. Hooked to a 2-stage, 15 SEER Condensing unit. The thermostat the is 2015 Lennox WiFi thermostat. Lennox iComfort Model 10F81
This is how it operates - Call for heat, the burner fires at 100% and fan at full speed. This will continue for 5 minutes minimum. I have tested this multiple times. Indoor temp at 62, setpoint at 69 (IOW, we've lowered the temp so the furnace doesn't run while we are away). System runs, for five minutes and the indoor temp might see a 3 degree rise to 65. I'll lower the setpoint to 66 and I can hear the system drop down a notch in fan speed. I'll bump the setpoint to 67 shortly to keep the burner on and it will continue in "low" speed.
The problem is when the setpoint is 69 and the indoor temp drops a half degree from setpoint or so, it fires at 100% and runs for 60-90 seconds. Yes, two problems in play - grossly oversized burner size for our area and it's in 100% mode.
I've asked the installing contractor about this and they've been out to check it and have assured me it's correct. I've also had a large Lennox-based contractor service the system and ask them, they say it's operating like it should.
Would suggest starting at the thermostat. Is it a communicating stat or does it have W1, W2, and R terminals? Pull it off the wall and check how it's wired. Take a picture and post it here if needed.
First, if it has W1, W2, and R terminals I expect that a separate wire is connected to BOTH W1 and W2. There should be two wires leaving the thermostat one connected to W1 and one to W2. If it doesn't OR the W1 and W2 terminals are jumpered together, call the contractor to make it right, because it isn't. (They may have done this because your thermostat wire doesn't have enough conductors for separate W1 and W2, and they didn't feel like running new thermostat wire...)
If it has W1 and W2 and R terminals with separate wires connected to W1 and W2 I would do this test:
(EDIT: Disconnect the R, W1, and W2 wires from the thermostat in case there is some internal problem with the thermostat that would affect the results of this test)
Jumper W1 and R with a jumper wire. Expected result: Furnace runs in low stage.
Disconnect and wait for furnace to complete cycle, then:
Jumper W2 and R with a jumper wire. Expected result: Furnace runs in high stage.
I also suggest running test directly at the furnace. I suggest disconnecting the R, W1, and W2 wires at the furnace before jumpering them there, to eliminate the possibility of a short between W1 and W2 wires in the thermostat cable.
The expected results of this test at the furnace should be the same as at the thermostat. If not a bad thermostat wire is indicated.
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Thanks for the heads-up - I'll ask about that - not sure if those meet code here.
The furnace-repair tech told me my old Carrier, at 80,000 BTU, is oversized - he recommended 60,000 BTU.
The house is a bi-level, about 1250 sq ft on the main level, insulated to R20 in the walls and c. R45 in the attic. The windows are tripanes.
Even 60K BTU probably sounds high to you, but bear in mind we hit -30 C pretty consistently, and -40 once in a while.
Is there an option in the thermostat to adjust the temperature "swing"? This might be in an installer menu. It might work better if the temp swing is set to be wider, like 1 or 2 degrees. And there may be other options to control the staging. But the installer manual for this thermostat doesn't seem to be available online.
I'm not too far south of you and sounds like our houses are nearly identical. I have a 60K BTU Trane S9V2 installed 2 years ago...love it and seems to be perfectly sized.
Why was the factory reps involved and need a factory start-up?
