hot water heater backdraft

2 months ago our hot water heater started back drafting out of the blue.
It’s not consistent, but when it happens, we can smell exhaust in our living area. Our landlord had several HVAC/Plumbing technicians came out and look at the issue, and none of them can identify the issue.
They think it may be the hot water heater unit from downstairs resident and also suggested that, even though our carbon monoxide detector have not gone off, but the exhaust we consistently breath in could be carbon burnout.

We share a common exhaust pipe with downstairs, and the condo management company refuses to let us install a separate piping (downstairs unit would not consider having their hot water heater examine either).

Our landlord have decided to stop investigating this issue, he taped up all the edges of the AC box so we won’t smell it as obvious in our living room and bedroom when it occurs?

We tested the back draft with a incense stick, we can see clear smoke being push out when it happens, but as soon as our hot water heater starts (it’s a brand new unit), the smoke would get push out as it should.

We need some help deciding if it’s safe for us to stay in this condo or if we should consider moving.
If there are any inspectors familiar with the area in Roswell, Georgia, I would gladly pay for a in home diagnostic as well.
Apparently everybody we had come in, either have no idea what’s happening or it’s not part of their expertise to look into it.

Thank you and if I post in the wrong section, my apology :frowning:

Contact your local fire department and explain what you just did.

I often check fuel burning appliances as part of my Energy Testing. There are some tests that can be performed by an Energy Auditor. I believe Georgia Power has a big involvement with Energy Efficiency in that state.

The building pressure can change. With the exterior temps getting hotter you can also be getting reverse stack effect. Your CO detector might not go off. The level needed to set off the detector won’t be high enough with a clean burning appliance. Low level exposure to CO can also cause health issues. The meter I use can detect even a small amount of CO in a room.

We did that and our local fire dept said that unless our condo is on fire, they can’t help us.

Thank you so much for a detail reply, that’s a lot more than any of the technicians told us so far.
Would it be a good idea to get a commercial CO meter to get a clear test on the CO level then?

Is there blockage of the flue? Perhaps by a bird’s nest.

Agree. Let the folks with some “authoritative clout” have a look-see. They won’t put up with any landlord BS!

Gas company too.

A plumbing technician went up the roof and look and said he didn’t see any blockage at all.
Our landlord called the gas company to check for gas leak (except it’s not a gas leak) and they didn’t find anything.
A local HVAC suggested that it could be downstairs hot water heater not burning correctly and it’s back drafting into our unit.
But when our hot water heater turns on, it would push the exhaust out and stop the back draft.

Because it doesn’t happen consistently (specific hour everyday etc) so our landlord said there’s nothing he can do and his best suggestion is to open the windows as much as possible to air out whenever there is a back draft??

He also suggest that the back draft may be normal? that the exhaust is not harmful?
Does this make any sense to anyone?

Thanks for all the help so far as well!
Our local HVAC companies are not that great, last guy after smelling the exhaust in our living room but couldn’t find a source, recommended spiritual adviser…

Carbon monoxide is just like water or electrical current it takes the path of least resistance. Did anyone check the type of fitting that your water heater has to the common pipe. it should not be a Tee type fitting it should be a Y fitting. It would seem logical to me that the downstairs WH was exhausting into your flue connection.

I agree that your water heater could help the other one draft. Someone should be testing the pipe for draft pressure. Depending on the temp outside the more draft is needed. So during the winter you might find it spills even more into your unit. The gasses are not healthy and it also introduces extra moisture. I would expect that if the current set up is allowed in your area they would require the flue pipe size going to the roof to enlarge where each water heater connects.

thank you so much for everyone’s help!
we do have a T fitting instead of a Y, but one of the HVAC technician insisted that switching the Y would not help with the exhaust and refuse to do the switch.
the draft pressure makes sense to me as well.
someone linked me this post -
where it said:
Both or all appliances have to be on the same floor. So, no furnaces in the basement or room heaters on the second level of your home.

does this also apply to condos or only homes?

A quick question, what kind of expert should we be reaching out to look at these issues and test the draft pressure etc?
Whenever we call a HVAC company in the area, they would tell me that I need to be speaking with a plumbing expert, and plumbing expert would send us right back to HVAC.

Any suggestion on that would be greatly appreciated!

The V in HVAC stands for ventilation, flue vents are ventilation of gas appliances its part of our trade. Sounds to me like the ones you have talked to don’t even know what field of work they work in. I would demand they separate the water heater vent to individual vents or I would move

my landlord insist that unless the issue can be reliably reproduce when the technician he calls out are on site, he would consider this a ghost issue, which i find ridiculously crazy.

thank you for all the help so far, ill definitely try to call some hvac experts today and hopefully someone can do a onsite examination for me.