Water heater flue tee connection

[Greg Jenkins]

Here is a picture of a water heater flue connection. It is a tee connector that serves the water heater and at one time, possibly the furnace. The furnace was upgraded and its flue re-configured.
The flue connection is in the crawl space.
Are openings permitted in the bottom of the tee or should it be sealed? Could backdrafting be a problem.

[John Dirks Jr]

Generally speaking, hot gasses will rise up the flue instead of falling out the bottom of that hole. Nonetheless that doesn't look right. Since the other appliance is now gone, there may be an issue with the flue being too large for the vent connector of the water heater.

There's enough going on there that I would have no problem calling it out.

...."have a qualified plumber or HVAC tech check this arrangement. Have them make any repairs or modifications needed to insure the maximum level of safety"......

Something along those lines.

[Scott Patterson]

Here is a picture of a water heater flue connection. It is a tee connector that serves the water heater and at one time, possibly the furnace. The furnace was upgraded and its flue re-configured.
The flue connection is in the crawl space.
Are openings permitted in the bottom of the tee or should it be sealed? Could backdrafting be a problem.

That is completely wrong. That setup was for two appliances, one is not connected and the tee needed to be removed.

Also, you need to take into consideration that the larger diameter pipe will allow for the flue gases to cool and not rise as they would if the pipe was downsized to one that was the same all the way to the exterior. You can see the condensation marks/stains (white stuff on the bottom of the open flue), this is telling us that the flue gases are cooling and not rising to the exterior. Good way and a very common way to introduce CO into the house.

I would simply say that flue pipe is wrong as it was designed for two appliances and now it serves one. Have a single "B" vent flue properly installed by a qualified person/contractor. If this is not done carbon monoxide could enter the home causing injury and or death.

[Greg Jenkins]

For discussion purposes, let's say the furnace is still connected to the flue. Six months out of the year,(during warmer weather) the furnace is not operating. What then? Do the flue gases from the water heater not rise properly. Or lets take it step further and say there is a heat pump installed with a gas backup furnace. On cool days when the heat pump is operating, do the flue gases from the water heater not rise and vent properly? It doesn't seem like a good design if proper ventilation of the water heater is dependent on the second appliance connected to the flue and operating.

[Bob Harper]

The vent should be suitable for the class of service. In the case with a orphanned water heater, the code 'recommends' it be replaced with a smaller, properly sized vent. Having that tee open allows excessive dilution air to cool the stack and hinder draft to the point you could get a CO problem. I would rip it out and replace with smaller B-vent to a bullhead tee with double acting barometric damper with a spill switch.

greg, you hit on a very important aspect--summer. ALL chimneys suffer in the summer. There is little to no natural draft. In order to draw, you need a high enough delta T WRT ourside the stack. However, in summer, you get a double whammy--warmer outdoor temps. and heater not firing. The result can be more damage and CO spillage in summer than winter. All the more reason for a properly sized vent. While we're on it, B-vent has a limited life. I recently researched the brands and only one carries a lifetime warranty and some are just one yr. If it's bad, replace it.

Greg, since this is in a crawl space, it is unconditioned and definitely must all be B-vent. Do you have clearance to that joist?

Good catch!
Bob