Went through 2 sets of electric coils on my Electric HVAC system last year. Could it be because of m

[lugoismad]

Ok, so here's the deal. I have a US Stove 1400 Wood Furnace along with a Goodman Heatpump / Electric furnace.

I had it installed August of 08. Used the wood for heat up until Christmas day, and decided to use the electric while we'd be gone overnight. And...it didn't work. The installer hadn't tested it since it was the middle of august when I had it installed. So he replaced it, no biggie. He said it was the sequencer on it.

He put a new one in, we tested it, all was good. So a few months later, again, we go to leave overnight and decide to use the electric backup. And again, it doesn't work. He comes out, says its another sequencer, and replaced it again. And again, it tests fine once an new one is in.

So...the two times I've tried to rely on this thing, its screwed me.

Here's some pics of my setup.

The furnace is in my garage.

And has an 8" and a 12" duct coming out of the top. In the back there is a duct going to my utility room to draw cool air from the house.

The ducts run over and tie into my 2 trunks. The 8" goes to the upstairs, the 12" goes to the downstairs.

On the left you can see the 12" tying into the downstairs trunk. The 12" duct on the right is what goes to the upstairs. About 8 foot up from the floor is where the 8" from the wood furnace T's into it. Both of the runs from the wood furnace have valves I can turn off to keep my cool air in the summer from running into the wood furnace and basically cooling down a big chunk of iron in my hot garage.

So I'm wondering if whats happening is hot air from the wood is running up into the HVAC unit in the last picture, and ....melting? something causing the electric coils not to work? I do know the hot air from the wood warped my plastic drain pan for the AC coils, and I had to have a new one installed last summer.

So I installed a piece of sheet metal in the inside of the HVAC unit keeping the hot air from the wood furnace from running back up through it and out my air returns I use for the heatpump and AC. Of course I'll have to remove this when I want to use the heat pump, AC or electric heat again. I'm thinking maybe the extremely hot air from the wood furnace messed up the sequencers? I know they are bi-metal based, maybe it heated them up to the point they no longer worked? I know what happened when the contractor came out and tested the broken coils was that only one set of electric coils was coming on, and the sequencer would never kick on the other two.

This year I'll be ordering a Honeywell sequencer instead of a Goodman, rather than having the whole set of coils replaced though.

Any other ideas as to what could be causing my electric coils to break on me?

 

[Gooserider]

I'm not 100% sure I'm following your setup description - are your wood furnace pipes blowing THROUGH your electric furnace? If so, I would say that I'd consider it quite likely that you are cooking the sequencers. In general it seems like a bad idea to have wood furnaces in series with the fossil units, no matter what type, and there can also be code issues if the hot air is blowing through the AC coils as well...

Any way you can re-plumb so your two units are running in parallel with each other, and have some sort of flapper so that the running unit can't backfeed through the non-running unit?

Gooserider

 

[lugoismad]

I'm not 100% sure I'm following your setup description - are your wood furnace pipes blowing THROUGH your electric furnace? If so, I would say that I'd consider it quite likely that you are cooking the sequencers. In general it seems like a bad idea to have wood furnaces in series with the fossil units, no matter what type, and there can also be code issues if the hot air is blowing through the AC coils as well...

Any way you can re-plumb so your two units are running in parallel with each other, and have some sort of flapper so that the running unit can't backfeed through the non-running unit?

Gooserider

No, they are not blowing throw the electric furnace. But I do suspect that some was backing up through the electric furnace and coming out the cool air intakes, since each furnace has its own cool air intake.

Like I said, I installed a piece of sheet metal in the electric furnace below the AC coils that I hope will prevent a lot of air flow from back up through there again. Its not air tight, but it should prevent a lot of the air flow from going back through the AC coils and out the cold air intakes for the electric furnace.


So just so we're on the same page....

Each furnace has its own cold air intake
They share the forced air ducts
I think the hot air from the wood furnace was backing up through the electric furnace and coming out its cool air intakes as well. I installed a damper to hopefully prevent this, but theres no guarantee it won't still get a bit toasty in there.

 

[lugoismad]

Here, I did my best to make a diagram.

The red line inside the electric furnace is where I installed a piece of sheet metal that fitted the inside of the furnace, to hopefully block air from going up through the cold air return for the electric furnace. The squiggly things are the electric coils and where the sequencers are at. I'd just take them out, but theres a ton of wires and without knowing a lot about it, I'd be afraid I couldn't get it back in ok when I needed it.

The obvious question is, why didn't you install that red plate any lower? I can't, thats as low as I can get to in the air flow of the electric furnace without physically unscrewing it and lifting it off the duct work. Which I don't have the know-how or strength to do.

Each furnace has its own return. The electric goes up to the attic, splits into a couple flex ducts and pulls from different main rooms of the house. It then blows into a duct under it, part of which T's off and goes upstairs for my 2 upstairs rooms.


The wood furnace is just putted up against my utility room and has a 3' metal duct that goes to a hole in the wall and into the back of a closet with a grate over it.

 

[laynes69]

Knowing nothing about electric furnaces I couldn't tell you whats going on there, but that ducting is too close to combustables coming off the wood furnace. Fossil, series on a wood furnace is one of the better, more efficient setups, when the woodfurnace is second in line with the central furnace. Coils don't get damaged, and theres no possible way for heat to go backwards through the ducting, but it must be done correctly with a unit that is designed for that type of setup. Lugoismad what temps are you seeing at the base of the electric furnace from the wood furnace, that will help determine if its an issue.

 

[lugoismad]

Knowing nothing about electric furnaces I couldn't tell you whats going on there, but that ducting is too close to combustables coming off the wood furnace. Fossil, series on a wood furnace is one of the better, more efficient setups, when the woodfurnace is second in line with the central furnace. Coils don't get damaged, and theres no possible way for heat to go backwards through the ducting, but it must be done correctly with a unit that is designed for that type of setup. Lugoismad what temps are you seeing at the base of the electric furnace from the wood furnace, that will help determine if its an issue.

Well I don't have an IR thermometer or anything, so all I can really say is the ducting is warm to the touch close to the electric furnace, but not uncomfortable to the touch.

I understand what your saying about putting it in series, but like I said before, that would mean I'd be heating or cooling a big chunk of metal in an unheated / uncooled garage whenever I'm not using the wood furnace.

I could move my flue thermometer over to the duct near the electric furnace, and can give you a rough rough estimate.

I think I'm just gonna take out the electric coils and just label all the wiring really well for when I need to put it back in. I'll just use some masking tape and number all the connections.

 

[lugoismad]

Here, I did my best to make a diagram.

The red line inside the electric furnace is where I installed a piece of sheet metal that fitted the inside of the furnace, to hopefully block air from going up through the cold air return for the electric furnace. The squiggly things are the electric coils and where the sequencers are at. I'd just take them out, but theres a ton of wires and without knowing a lot about it, I'd be afraid I couldn't get it back in ok when I needed it.

The obvious question is, why didn't you install that red plate any lower? I can't, thats as low as I can get to in the air flow of the electric furnace without physically unscrewing it and lifting it off the duct work. Which I don't have the know-how or strength to do.

Each furnace has its own return. The electric goes up to the attic, splits into a couple flex ducts and pulls from different main rooms of the house. It then blows into a duct under it, part of which T's off and goes upstairs for my 2 upstairs rooms.


The wood furnace is just putted up against my utility room and has a 3' metal duct that goes to a hole in the wall and into the back of a closet with a grate over it.

maybe the forced air from wood furnace is rising thru the not running electric furnace which has cold upper area from venting into cool attic & the warm air is depositing humidity in the e furnace because it is cooler.

That would make sense.

I just went to the hardware store and bought some spade connectors. I'm going to turn off the power, label the wires and connections, and remove the e-coils.

 

[lugoismad]

maybe the forced air from wood furnace is rising thru the not running electric furnace which has cold upper area from venting into cool attic & the warm air is depositing humidity in the e furnace because it is cooler.

Well, I guess I solved my problem. The e-coils are sitting in a box next to the furnace. I turned off the breakers to it and labeled all the connections so I should be able to have them back in in about 20 minutes in the spring or if I ever need to use them.

I was looking for a solution to not have to do that, but this seems like the cheapest and easiest solution.