Vent configuration

[Jon mackay]

This furnace has a vent configuration where there is an inducer fan that causes the water heater to backdraft when the furnace first starts. As soon as the furnace burners come on and the flue heats up, everything seems to draft fine.

Is this acceptable if all systems draft properly within 1 minute? Additionally, are you allowed to increase the vent size right out of the heater cabinet like that?

Also, there is a flue liner that uses the old asbestos chimney for a pathway, looked ok but I wanted to double check.

[Bob Harper]

Where to start?

Yes, you are allowed to common vent a CAT I fan assisted furnace with a natural draft water heater even though it isn't a good idea for the reason you described. I have written here on this set up before but a blocked flue will vent out the WH draft hood.

Often the sizing charts will require upsizing for vent connectors, esp. when manifolded into a common vent or when the vent rise is short.

-clearance to pipe insulation on WH
-support of single walled pipe inadequate
-homemade unlisted firestop/ wall penetration as a combustible wall pass-through
-clearance from single walled connector and liner to combustibles
-If this is a listed liner installed into Transite cement asbestos vent, then that is a problem. These liners were tested and listed inside a single brick wythe "chimney"--not vents. How is this liner supported? Any pics of the termination? Even that Transite is installed at zero clearance to the subfloor.
-because of the proximity of the work area, you could make a case that the vent connector needs to be protected from damage in addition to being B-vent.
-do you have 30" wide by 36" out in front of that furnace cabinet to work?
-min. 3 equidistantly spaced screws per joint?
-do you have adequate makeup air?
-that WH needs a 4" vent connecor-not 3"
-are those ducts sealed?


HTH,

[Jon mackay]

Here is the termination at the exterior.
I'm not sure whats holding up the transite pipe.

[Bob Harper]

I like the listing label where it states to install only in a masonry chimney.

I don't see a means of support for the liner or Transite, which btw is improperly shingled.