View Full Version : Furnace Cycling
11-09-2008, 02:51 PM
I recently replaced a 30+ year old Lenox furnace with a Goodman 95%, two stage, variable speed and a White-Rodgers two stage stat. I am sitting here today with the stat at 70 and the outdoor temp is 23. The furnace seems to be running almost continually. On in 1st stage for approximately 10 - 15 minutes and off for only about 5. So it cycles on and off about 4 times each hour. Is this normal and if so what can I expect when it gets down to below zero. Did some research and found one site that said these types of furnaces are designed to cycle on and off 4-6 times each hour. Would like to know if it is operating properly or if I need to get my contractor back out. Any advise would be greatly appreciated.
Thanks in advance,
the dangling wrangler
11-09-2008, 03:57 PM
I think you answered your own question.
11-09-2008, 04:03 PM
Could be that your installer needs to fine tune the settings or the furnace could be oversized for your home. Did the company that did the work do a load calc on the home prior to installing the new furnace or did they just go by what the size furnace they replaced ? If they sized the new furnace based on what they replaced I would call the owner of the company and ask him for a copy of the load calc (if they did one) or have them do one and size the furnace accordingly, and if they oversized the new furnace I would aks that they replace it with the correct size needed for your home.
tinknocker service tech
11-09-2008, 04:44 PM
if it is running in low stage and then sutting down and maintaining temp then i tend to think it is working.
your stat may be set for 4 cycles per hour and can be changed if need be.
at zero i would think it will be running longer and also kicking into second stage to reach and maintain temp.
call the installer and have it checked to be sure it is doing what it is designed tto do or if something is wrong
11-09-2008, 08:01 PM
Yes, it appears to be running just fine on low stage but wondering if I need to check my LP tank to see if I have any gas left. Perhaps I just need to get used to it. However, since it it a cold November day and I don't have enough to do, it fires up for approximately 7 minutes each cycle, rest of time is fan time, which equals out to about a half hour burning gas each hour. Since it is on low stage, only burning about 49,000 btu, am I stilling obtaining my energy efficiency? Always hard to get used to something new and you know the old saying, "if it works don't fix it.
tinknocker service tech
11-09-2008, 08:15 PM
first off 2stage and modulating furnaces are mainly for comfort not eff. There is a long tread on this if you do a search you should find it. Your unit is rated but if sized properly it is going to give you uniformed heat through the house and a more comfortable level through out.
Effiency does play a role and you are getting what you paid for but you should also be getting better and a more even temp zone
you will also find the cycles per hour give you more comfort without temp swings so 70 is just that and no over shooting or waiting for the house to cool off before the heat comes on to heat it
sounds like it is working fine
11-09-2008, 08:26 PM
Whether your furance is operating normally as you described its operation is a function of the thermostat. There are two ways to wire a Goodman 2-stage furnace. The first way is to use the existing or new 1-stage capable t-stat. In that case the thermostat will call for heat and the furnace will run approximately 10-minutes on 1st stage, then if the call for heat continues it will step up to 2nd stage. That's called staging based on time.
The better way, which gives the greates comfort, is to have a 2-stage thermostat connected to the furnace. In that case the thermostat controls the staging and can start on 1st stage and keep it there 24/7 if necessary and/or cycle 2nd stage on/off as needed. It's all about maintaining thermostat set-point. If you set the stat for 70 and the temp starts sliding down to 69, a 2-stage stat will bring on 1st stage heat. As long as it can maintain or increase the temperature with 1st stage, it'll keep the furnace running on 1st stage until either the room temp reaches 70 (the set-point) or just keeps chugging along, holding the temperature at 69.5. When the temperature can no longer be kept at 69.5, the stat will cycle the 2nd stage heat on to bring the room back up to 69.5. First stage will continue to run and 2nd stage will then cycle off. If the temp slips again, 2nd stage will be brought back on and kept on as long as needed. The length of operation of 2nd stage will vary, just as 1st stage will vary, denpending on the outdoor temperature/heat loss from the home. Whenever possible we install 2-stage units with 2-stage stats so the customer gets all the comfort from the system. IMO, otherwise it's too much like a 1-stage furnace and they're not getting all they thought they paid for.
11-09-2008, 10:13 PM
If it's 23 I'd think that thing shouldn't shut off. What's the design temp where you live?
Although startup and shutdown losses on the new systems are quite small, they still exist. The advantage of multi-stage is they can run continuous under light loads. An over sized unit hit's too many off-ramps. You want to stay on the highway as long as possible to get your highway mileage and seems 23 degrees should have you there on low fire.
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