Anyone know anything about electric furnaces?

[Prof]

So I heat exclusively with wood. That was my intention when we designed and built our house. However, we couldn't have wood as our primary heat source according to code, so I had an a 15 KW (around 50K BTU) electric forced air furnace installed with a 3 ton blower. I never really use the thing, but turn it on 1-2X per year just to make sure it works. Yesterday, I decided to actually let it bring the house up from 65 to 68 degrees. It did this in about 20 minutes or so. I then noticed the furnace was short cycling 4-5 min on and 4-5 min off. I let it do this for a couple of hours thinking that it needed to reach some type of equilibrium. I didn't have any type of wood fire going for a couple of days at this point. Anyhow, after a couple of hours, it continued to short cycle. I inspected the air filter (it was fine) and changed the batteries in the thermostat--no difference. I was planning on having a heat pump installed this summer, mostly for cooling (of course given the pandemic this might not happen), but was hoping that this furnace could serve as the back-up to the heat pump in extreme cold. Any ideas on what might be the cause of the short cycling? I'm going to have a pro do the heat pump, but I'd appreciate any advice that might help me have an informed conversation with the HVAC guy.

 

[brenndatomu]

Is it blowing warm or cold air?

 

[andym]

When you say the furnace was shutting off do you mean the blower or the heating element?

I'm wondering if your blower is sized correctly? Too small and the elements will overheat shutting the unit down.

 

[Prof]

Is it blowing warm or cold air?

Warm--it didn't seem to have a problem bringing the house up to temp.

 

[Prof]

When you say the furnace was shutting off do you mean the blower or the heating element?

I'm wondering if your blower is sized correctly? Too small and the elements will overheat shutting the unit down.

Blower--not sure about the elements. The unit was a package deal, blower and elements came together without me having to choose options.

 

[brenndatomu]

So it is short cycling while the heat is "on", or after the tstat has been satisfied?

 

[AlbergSteve]

What is the make and model of the thermostat that was supplied with the system? On some thermostats you can change the hysteresis or deadband, the temperature differential that the thermostat turns on and off. If you upgrade to a smart stat, stay away from Nest, deadband is not adjustable. The Ecobee however is adjustable up to 2.5F.

 

[andym]

Blower--not sure about the elements. The unit was a package deal, blower and elements came together without me having to choose options.

My only experience with electric furnaces comes from people installing them as temporary heat during new construction. They are old units so may be different from yours....I think the elements turn on and off separately from the blower. If the filter was too dirty or something restricted the elements would trip some kind of reset and go into a cool down mode. This in turn soon caused the blower to stop.
However, you checked the filter and it sounds like the blower is correct size. The fact that it warmed up your house that soon tells me the elements are working properly, but there is something not right in the blower wiring. Is there a snap disc or something that turns on the blower?

 

[Prof]

My only experience with electric furnaces comes from people installing them as temporary heat during new construction. They are old units so may be different from yours....I think the elements turn on and off separately from the blower. If the filter was too dirty or something restricted the elements would trip some kind of reset and go into a cool down mode. This in turn soon caused the blower to stop.
However, you checked the filter and it sounds like the blower is correct size. The fact that it warmed up your house that soon tells me the elements are working properly, but there is something not right in the blower wiring. Is there a snap disc or something that turns on the blower?

I'm not sure--to be honest, this is a little out of my wheel house. I just want to have some ideas and not be pushed into replacing the furnace if there is a relatively simple fix. Thanks

 

[Prof]

So it is short cycling while the heat is "on", or after the tstat has been satisfied?

After the thermostat has been satisfied. It doesn't drop a degree before turning on again. I'm starting to wonder if it isn't a thermostat problem.

 

[Prof]

What is the make and model of the thermostat that was supplied with the system? On some thermostats you can change the hysteresis or deadband, the temperature differential that the thermostat turns on and off. If you upgrade to a smart stat, stay away from Nest, deadband is not adjustable. The Ecobee however is adjustable up to 2.5F.

Not sure what the model is, but it is the most basic honeywell, just 4 buttons and no frills.

 

[andym]

After the thermostat has been satisfied. It doesn't drop a degree before turning on again. I'm starting to wonder if it isn't a thermostat problem.

I apologize. I did not read the first post well enough. Definitely thermostat related.

 

[Gearhead660]

What is the make and model of the thermostat that was supplied with the system? On some thermostats you can change the hysteresis or deadband, the temperature differential that the thermostat turns on and off. If you upgrade to a smart stat, stay away from Nest, deadband is not adjustable. The Ecobee however is adjustable up to 2.5F.

I would check to see if your tstat is adjustable. Usually just flicking a switch on the back side.

 

[brenndatomu]

Yup, sounds like a tstat issue...either needs some adjustment/setting changed, or changed out all together.

 

[semipro]

Some thermostats have mechanical or electrical adjustments for cycle duration.
It might also be thermostat placement if it's in a location where warm air from a register is blowing on it.

 

[MissMac]

not sure what kind of tstat it is, but it could be the threshold for starting up a new cycle is really small. so for example, if your tstat is set at 20*C, but your tstat is set to call for heat when the temp drops by 0.5*C below what you've set it at, then this can cause short cycles. I had the same issue on an old tstat. if you have a way to check the 'spread' of the threshold for calling for heat, this is what i'd do first. I have an ecobee tstat now, and I've set it up so that the furnace wont' call for heat until the temp drops 1.2*C below whatever temp I've got it set for. hopefully I explained that well enough.

hope you can figure it out.

 

[MissMac]

What is the make and model of the thermostat that was supplied with the system? On some thermostats you can change the hysteresis or deadband, the temperature differential that the thermostat turns on and off. If you upgrade to a smart stat, stay away from Nest, deadband is not adjustable. The Ecobee however is adjustable up to 2.5F.

This! much better said than my ricky-bobby explanation.

 

[Prof]

This! much better said than my ricky-bobby explanation.

I think you are likely right. I have a Honeywell 5000 (took a little internet digging for me to figure this out). Unfortunately it seems that the way mine is set up it is not giving me the option to adjust the cycle rate or a bunch of other things that the manual indicates that I could adjust. If it wasn't for the COVID-19 isolation, I doubt I would have ever noticed this, since I rarely use the furnace. I feel better though narrowing things down to the thermostat. I am planning on having a heat pump tied into my system and I really didn't want to get another furnace and blower.

 

[brenndatomu]

Honeywell 5000 Series Thermostat User Manual

 

[Prof]

Honeywell 5000 Series Thermostat User Manual

So I downloaded a copy of this the other day and was at a loss. I had myself convinced that I didn't have access to what I needed to change the number of cycles. I opened the link you shared and there it was clear as day (even though it is no different than the one I had). Problem solved, thanks!

 

[brenndatomu]

So I downloaded a copy of this the other day and was at a loss. I had myself convinced that I didn't have access to what I needed to change the number of cycles. I opened the link you shared and there it was clear as day (even though it is no different than the one I had). Problem solved, thanks!

Its an Easter miracle!
Glad to have "helped"...hopefully changing the setup there will solve the issue.

 

[AlbergSteve]

If you do a bit of digging you'll see that most, if any, Honeywell stats do not support deadband changes. Changing cycle times might help.

 

[Prof]

If you do a bit of digging you'll see that most, if any, Honeywell stats do not support deadband changes. Changing cycle times might help.

That's what I did and it seems to have solved the problem.