Professional Member
I'm a newbie heat pump owner and will try my best to describe my concern.
I have a split system Luxaire 92% efficient propane fired updraft furnace and outdoor 12 SEER York heat pump. The setup is such that the furnace is stacked on top of the indoor coil. The order is cold air return to indoor coil to furnace to plenum to trunk. I think it was setup out of laziness by the previous owner when he ripped out the older electric furnace and just stacked propane furnace instead of rearranging everything.
I've had 4 different techs work on this system for periodic maintenance and other things. All have said the coil is in the wrong place, and should be above the furnace. That is it should go cold are return to furnace to indoor coil to plenum to trunk.
The youngest tech, a pimple-popping fresh out school cocky teen, was appalled at this setup and gave other wrong information. I give his opinion the least weight. One older gray-haired tech who really seems to know his stuff from what I can tell, measured delta temperatures (inside the plenum to outside) in heat or cool mode at the plenum (just above the furnace) and said they were "textbook" (i.e. prefect).
Still no one has explained why this setup is wrong. In fact, the older gray-haired tech said this setup might have the advantage of being able to run the HP and furnace in tandem, instead of exclusively.
Can anyone tell me if this is wrong, and if so why? And how bad is it?
God Speed, Jim. We'll miss you - 2-26-23
The problem is that in the summer when the A/C is running. That the heat exchanger of the furnace can become cold enough that moisture condenses inside of it, and rust out the heat exchanger.
There is no 100% yes it will rust out teh HX, but the chances are very good.
Can you post the mod number of the furnace, and post pics of the indoor set up.
Yours isn't the first one set up like this.
Professional Member
not just wrong,way wrong.
Professional Member*
Freon leak in coil could result in phosgene gas poisoning.
__________________________________________________ _______________________
Experience is a hard teacher because she gives the test first, the lesson afterwards" ~ Vernon Law
"It's what you learn after you know it all that counts." ~ John Wooden
"When the teachers become unteachable we're all in trouble" ~ Mr. Bill
"Remember "Pro" is only a name, it's not always a mindset determined to do everything correctly" ~ Mr. Bill
Professional Member
r22jjc, I greatly appreciate your input, but could you elaborate.Originally Posted by r22jjc
Professional Member
Will post all model numbers tonight when home, but I should add we rarely ever use this system for A/C. With a whole-house fan, celing fans, pool and local temps avg 80s, and wifey likes it warm we just don't bother with the A/C.
Professional Member
That sounds scarey. Are you saying my indoor coling placement has me at greater risk of a leak?Freon leak in coil could result in phosgene gas poisoning.
Isn't anyone with a coil in their air stream at risk of this? Please elaborate.
Professional Member*
No not coils "downstream" from the furnace.
__________________________________________________ _______________________
Experience is a hard teacher because she gives the test first, the lesson afterwards" ~ Vernon Law
"It's what you learn after you know it all that counts." ~ John Wooden
"When the teachers become unteachable we're all in trouble" ~ Mr. Bill
"Remember "Pro" is only a name, it's not always a mindset determined to do everything correctly" ~ Mr. Bill
Professional Member
Phosgene gas: If your coil is BEFORE the furnace, leaking refrigerant could pass through the furnace heat exchanger while the furnace is running. It might just be hot enough to break down the refrigerant, creating the dreaded phosgene gas.
If the coil is AFTER the furnace, any leaking refrigerant would still end up in your house, but would remain as an inert gas.
Unless you have a stainless steel heat exchanger, the coil before the furnace will rust out the heat exchanger during the a/c season, as been there posted above. Then you get to deal with the deadly CO gas. To me, this is a far greater danger.
Regular Guest
wow
hi im in houston and i got to say if we had a coil on the back side of a furnace youll have water everywere with the hummidity we have
so you have an up flow coil and furnace the mfg will tell you this is a blow thru coil not a suck thru coil it would effect the the way the condinsation runs down in to the drain pan....
and if you should have a freon leak it is oilbased and will stick to the heat exchanger and in heat mode will burn off a gas that can kill you.....
get a pro and have it installed properly....
God Speed, Jim. We'll miss you - 2-26-23
Oil travels with R22.
Professional Member*
No he can't
As beenthere and Mr Bill have stated there are many reasons how this kind of setup can not be good. Is it a sure thing that you are going to have a rusted heat exchanger or phosgene gas?? No it isn't. If you were my customer I would probably recommend you have it fixed. However, I would have to weigh that against it's age and efficiency and if putting more money into it woulf be worth it....might be better to let it go for a while and replace the entire system with something that will save you money down the road.
I need a new signature.....
God Speed, Jim. We'll miss you - 2-26-23
Oil travels with R22.
Professional Member*
How did you do that??
I need a new signature.....
God Speed, Jim. We'll miss you - 2-26-23
It would be possible. But last I knew, R22 had to reach a temp of 500°F in order to begin to decompose into phosgene gas.Freon leak in coil could result in phosgene gas poisoning.
God Speed, Jim. We'll miss you - 2-26-23
Who do what.
Professional Member
There's no way that set up would pass an inspection,at least in my area. As others have said,phosgene gas (kinda like the stuff in WW1) is a possibility with a fuel burning furnace.
God Speed, Jim. We'll miss you - 2-26-23
Its just as much a possibility with an electric furnace with the coil before the strip heaters.
Professional Member
OK I'll give you that one,but I thought we were talking about a propane set up.
God Speed, Jim. We'll miss you - 2-26-23
We are, but your post made it sound like only fossil fuel systems have this problem.
Heat pumps are just as likely to have as fossil fuel furnaces.
In reality, the chances or creating phosegene gas is slim.
Rusting out the HX, high chance.
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