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Discussion Starter · #1 ·
Hi everyone
I need help with a complex air flow/temp imbalance, that so far no one can fix. I'm not sure if I need HVAC or an engineer; but I need a genius.
I have an up/down duplex (900 sq ft each apt) with a forced air, natural gas furnace, installed in Jan 2010 with a new programmable thermostat . Before it was replaced I had an oil furnace, and I lived in the downstairs apt -never had problems with temp swings. The apt was comfortable.
The new gas furnace stopped working during a very cold spell in Dec 2016, and was repaired after 2 days.Here the problems begin. During those days I opened all the dampers-and didn't mark their positions-a mistake I will never repeat.
Now each winter (randomly) the downstairs tenant complains that it's cold and sends photos of a thermometer showing 62 or 64 degrees. So the upstairs tenant, who controls the thermostat, turns up the heat. When she turns it up from 68 to 70 his apt gets way too hot (76 or 78 degrees-he sends photos-he is telling the truth)
Since his downstairs apt gets way too hot with thermostat at 70 I don't see how to fix this. If I close down the dampers to the thermostat then the furnace will run more-he will be too hot. If I leave them open the heat will turn off faster-he is too cold.
Why does he get not enough heat and then too much heat? Why doesn't he have a problem all the time? It seems to be the worst when weather is not too cold, but maybe he just doesn't tell me all the time.
A few things I've considered since reading on this website, mostly the threads by USER_12345a (yes, I'm sucking up now-hoping he will read this and jump in).


1-The return for the first floor apt is inadequate-and the apt is pressurized until the call for 70 degrees overcomes that pressure (not sure how). The return is inside a closet on the floor. He says it's not blocked but with closet door shut does it get enough return?


2-The return upstairs is blocked (not sure how that would affect the system, but we had to take the fins out of her return years ago to keep her from closing it).


2-There is some kind of 2 stage blower involved (or modulating) which doesn't work on low, but when on high and overcomes the pressure, or something similar.


3- I've asked the upstairs tenant to run the fan in ON mode. She claims she did that days ago. The downstairs tenant claims the fan is not running. Is the fan the problem?


4-One or more supply ducts are dented or otherwise not sending heat. I did not see any damage.



5- I'm considering that other 4 or so tenants (after new furnace and before this tenant) have been too cold and too hot and have not complained about it. That is, I lived there comfortably but that was with the old furnace. I'm trying to get that info now from past tenants.


I've tried to think of this as a “cold rooms in house” problem since the apts share returns and supply, (but obviously no open stairs between apartments) but nothing solves the too hot problem. To complicate things we don't live there and have a hard time getting HVAC, us and two tenants to stay there long enough to figure this out. The company that fixed the system is willing to show up, but how long can they stay in the basement asking tenants about the temperature? Would they be able to figure out something else by seeing the system? FYI the guy who installed the furnace does not return calls, to me or others. He did not do any new room calculations before installing that I know of.
Thanks in advance for ANY help. If I need a specific kind of HVAC person or engineer please tell me where I might find that person. If I need specific tests done please advise.




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To start things off, I'd lock the thermostat. I never trust what people say, you just never know what's going on in their head. Set it to 70, and the fan set to on. You may need a locking cover.

Start with all the vents open, and adjust his dampers closed if he's too hot. Adjust hers closed if he's too cold. Take your time at this, make small incremental changes.

All returns really need to be open. A closed closet door is probably not letting enough air under it. The location may need to be adjusted.

There's plenty of tests that can be done, but I'm trying to keep things simple for now. The most important measurement is going to be the temperature rise. Measure the temperature entering and leaving the furnace while it's on. The rating plate will say what the limits are. If you're too high, you have to open some of the vents you just closed.

What is the model number of the furnace?

Cheers!
 

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Discussion Starter · #3 ·
It's a Tappan two stage (no modulating) but I forgot to get the model number.

I met an HVAC guy there today (he said it was a cheap "box store" quality furnace"-I'm not surprised)

First he said close the downstairs apt. dampers-to which I said, "wouldn't the tenant be more cold because more heat upstairs would satisfy the thermostat faster?", and he agreed. Then said, "close the dampers going near the thermostat upstairs", and I said wouldn't the downstairs tenant be too hot?" and he agreed.

Maybe this is not a balance/ air flow problem. It is too cold and then too hot in the same space .....what could cause this?

He disconnected the stage 2 function, opining that if stage 2 didn't kick in there would be more time for warm air to satisfy thermostat, before first floor tenant melts.

Also, he thought it possible that the spread between the existing room temp (say 66) and thermostat (when manually changed from 68 to 70) might have caused the stage 2 to engage, and overheat downstairs. So, maybe leaving it at 70 all the time is a better answer-then no urgent call for heat.

I'm baffled and I think there is more to this than damper adjustment. Any of you guys have ideas?
Great idea to lock the thermostat, because you're right-I don't really know what they are doing. I only know what they say they are doing. I probably could also monitor this with an app of some kind.
 

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My $0.02 is the upstairs tenant likes it cool. When she is forced to turn up the thermostat she used to close the return air duct, assuming this would make it colder.
Since you put a stop to that she probably just throws a towel on top of it and in addition opens the window to cool off. And it does cool off. Which causes the thermostat to constantly call for heat.

I would not lock the thermostat. I would disconnect it. Then I would install real thermostats in the return air ducts that are remotely controlled and then turn the fan on 24x7. This is common in commercial buildings because it lets the occupants play with the thermostat all day long to get it "perfect" And I also would put a vent in the closet door.

But ultimately I think it's impossible for you to get different temperatures in the different units with a single furnace no matter what you do to the system, and I strongly suspect your tenants prefer different temperatures.
 

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I'm surprised you got an occupancy permit with a return in a closet, since that is a code violation.
 
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Put up a picture of the furnace installation, depending how the furnace hot air output ducting was designed, it may be possible to easily convert to a two-zone system. With a simple two-zone system, each tenant could have their own thermostat even though they share a furnace. That's the solution that would be the most comfortable for the tenants.

Alternately you may be able to have manual dampers put in right after the furnace to throttle back the flow to one of the units.
 

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Put up a picture of the furnace installation, depending how the furnace hot air output ducting was designed, it may be possible to easily convert to a two-zone system. With a simple two-zone system, each tenant could have their own thermostat even though they share a furnace. That's the solution that would be the most comfortable for the tenants.

Alternately you may be able to have manual dampers put in right after the furnace to throttle back the flow to one of the units.
This would likely cause significantly restricted airflow which could compromise the equipment.

Cheers!
 
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