Better check that HX carefully. It's likely ruined by now.
Went to a house today that complained of water dripping from the furnace. The setup is an older horizontal gas furnace with a evap coil on the return side. The water is dripping from the heat exchanger chambers. There are 6 vertical chambers in the furnace and water is running down the insides of all the chambers. I haven't ran across this before, but my first guess is that warm outside air (90-100 degrees for the past three weeks) is coming down the flue pipe and condensing as the heat exchanger is in the cold air stream and around 55 degrees.
Does this sound reasonable to you guys? Would it help to add a damper to the flue to stop the warm outside air from traveling into the heat exchanger? Or do you think I have something else causing the condensation problem?
Thanks
Josh
Better check that HX carefully. It's likely ruined by now.
Having the evaporator before the heat exchanger in the air stream is what is causing your problem.
And most likely your furnace/heat exchanger is rusted out and will need to be replaced.
Like Baldloonie said Check it carefully because there are most likely issues with it
That's against code up here.... Bad news!
Where is the filter in this set up? I can't imagine the air flow being very good
Evaporator before heat exchanger is not right.
That's truly a "condensing furnace", and is about to become 90% efficient - at gassing people. Good fodder for the Wall of Shame forum.
Most are, and rot out in under 10 years in a lot of cases!
Where is the furnace located? Do they ventilation running? What type of ignition system?
Always here
The last time I saw that on a residential furnace, the heat exchangers were gone when the furnace was 7 years old. Amazingly, the guy who installed it was actually a Lennox dealer who I knew. It was already configured that way, so I guess he thought it was ok to just throw in a new furnace without correcting the problem. Not hard to guess why the one before it conked out.
This is an old natural draft furnace. Is it possible that the hot outdoor air would travel back down the flue and condense on the walls of the cold heat exchanger?
I did notice the pilot was on so I shut it off. Not sure how much moisture would come from just the pilot flame.
It's more likely the humidity from where the furnace is sitting is condensing. If your flue is back drafting you have even bigger problems!
Once that HX gets cold it's gonna act like a 2nd evap coil condensing whatever moisture is in it, since it's an older natural draft furnace it will probably take longer to heat back up to ambient, compounding the problem.
What make is the furnace?
does not need the chimney back drafting to cause the condensation.
the heat exchanger is after the evap coil so it is cold, it would probably sweat even if the chimney were disconnected.
if its a horizontal system in a damp crawl space it would even be worse.
only solution is to reinstall it properly, probably with a new furnace at this point.
The reason I am confused is that there is about 10 foot of uninsulated duct between the evap coil and the furnace and it is not sweating. I thought that would rule out high humidity in the furnace room being the cause.
That is why I was wondering if the outdoor air from the flue would be related to the issue.
Like someone said the hx is prob acting as another coil. The hx is prob slowing the air down enough that it will start to condense on the warmer metal. How hot is it in the basement?
The HX has a lot more surface area than duct work does, obviously to promote heat transfer. It's now working in reverse, and is probably garbage.
I don't know what code you have where you're at, but you can't generally add a damper to a flue, if the appliance isnt approved for one. If you can, you better make damn sure it proves open before the gas valve opens. Guaranteed this won't solve your problem though.
I will check back with them tomorrow to see if the pilot was causing any problems.
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