Thread: Order of Vented Appliances

I know that a "smaller" BTU appliance is to be vented after a "larger" BTU appliance, but isn't there also a rule about a draft hood to be installed before a fan-assisted? Yesterday I had a 110,000 BTU fan-assisted furnace installed and two 50 gallon (40,000 BTU) draft hood water heaters at the end of the run (see attached photo). There were signs of backdrafting at the furthest water heater around the draft hood. Am I correct that the fan-assist should be at the "beginning" instead of the "end"?

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Wow there so much wrong in those pics. I've actually tested back draft on water tanks when the furnace kicks on in those set-ups (air flow meter).
Beyond the configuration I think there are more immediate problems causing the backdrafting. The length of the run and the elbows on top of the draft hood. They should have a 12" rise on the hood before any elbow. From my experience the 90's on top of the hood cause the worst backdrafting issues. How long is that horizontal run, 8-10'? I would obviously recommend changing the flue configuration and possibly the tank.
A few other notes:
- What's with the TPR next to the hood? Those look like newer tanks. I didn't think anyone was doing TPR's in that hole anymore. That's usually a plugged tap hole. I'd look up the Manuf. sheet and check the TPR location. Doesn't seem right.
- exposed fiberglass itch
- vent fan on furnace clearly dirty - clean & service unit
- air gap at AC drain capped
- Not liking that transformer on the romex box, probably non-compliant wiring
- damaged insulation around ducts
Hope that helps.

Reis,

It's quite possible the vent connector for the water heaters are too long.
General rule of thumb is 1 1/2 times the diameter of the vent connector in (inches to feet). So, if the vent connector from the water heater is 4 inches, the offset to the chimney or vent should be 6 feet max.

see the attached.

I might also add the B vent from the far HWH looks to be joining the run on a 90.
Are there any supports holding it up?