Orphaned gas water heater situation? And what to do about it

[Mittenstate]

My house in Michigan was built in 1995. Last year I upgraded the 80% efficiency gas furnace to a 97% efficiency furnace that vents directly outside. Consequently I now have a chimney that vents to the roof that is only used by the ~2013 gas water heater. I'm now doing research before upgrading the water heater and was concerned to learn that I might be in an "orphaned water heater" situation. The well-regarded company that installed the furnace came by to provide a quote on the water heater replacement and assured me that my setup is not a problem because my chimney is metal rather than masonry, and that "orphaned water heaters" are only a problem for masonry chimneys in older houses. On my read the IFGC 501.15 seems to suggest that the chimney does need to be resized, but the experienced company employee assured me that my chimney is the right size and that it wouldn't be possible to run a liner down it anyway as liners aren't small enough to fit. I measured the bottom of the chimney where it joins with the water heater stack and it's about 5". I read on this forum that liners can range from 3-4", so that doesn't seem correct.

Yesterday I did a back flow test (windows all closed, turned on all bathroom fans, ran furnace, turned up water tank to force it to run, 30 degrees outdoors, but very little wind) and found that under those conditions the chimney was not back flowing. I do have some evidence of back flow as the gaskets around the hot and cold water pipes are warped, but I believe that happened prior to the installation of the new furnace.

Ultimately the reason this all matters is that if I am in an orphaned water heater scenario I don't want to run the risk of back flowing fumes or the chimney developing leaks over time due to condensation of vapor. If that's the case then I'll probably spring for a tankless unit that vents directly outdoors ($5000 installed). If not then I might have another standard tank model installed ($2500 installed).

Photos linked here in case it helps with analyzing the situation. Thanks in advance.

 

[Fitter30]

Run a 93% furnace on pvc flue and fresh air and 50 gallon nat gas water heater for 28 years. Never had a co detector go off next to the heater and yes the plastic grommets were distorted. Its not that the 5" flue won't take a liner it the screws the install people might have used.

 

[Sponsor]

 

[Master Plumber Mark]

We see this issue all the time.... I let the customer know about it and leave it at that...
I normally go ahead and install the water heater and if they decide to put in a liner at a future date then
they can spend the money at that time.... Most times the furnace was changed out years ago
to 90% and nothing was done at that time and it all works fine anyway....

I have the same thing in my home presently and its been this way since about 2005..
It will work perfectly for somewhere between 30 to 90 years......

Install a carbon monoxide dectector if you are worried about it and leave it be..

 

[Fitter30]

You should realize that in non heating season the furnace hasn't been running.
With a low CO level (50 ppm), it may take up to eight hours for the alarm to go off.

 

[Master Plumber Mark]

You should realize that in non heating season the furnace hasn't been running.
With a low CO level (50 ppm), it may take up to eight hours for the alarm to go off.

I should have taken a picture of the job I was on yesterday installing a water softener... I thought
about doing this but it slipped my mind..

A 110 year old house.... it has a brick chimney and it had both an abandoned 5 inch flu pipe for the
furnace capped off and the water heater was still going up that vent on a separate 3 inch flu pipe.....
The owner is aware of this but its not high on his list of concerns........

I told him to install a carbon monoxide
alarm above the water heater if he was worried about this....
He was not worried and I finished my work and moved on to the next event for the day

 

[John Gayewski]

A standard carbon monoxide detector doesn't detect carbon monoxide. Sounds weird. It does detect it, but the Alam doesn't go off unless it has been detected above a certain amount for a certain amount of time. If your water heater is back drafting carbon monoxide the Co detector could very easily miss it. Or decide it's not dangerous and just let it keep going.

There are more sensitive detectors for people who actually want reliable info. Standard detectors basically tell you that you'll be dead pretty soon instead of hey your being poisoned.