View Full Version : Appliance venting

Richard Roshak
05-03-2008, 07:19 PM
11 year old home. Two 40 gal water heaters and one 125,000 80% heating unit all venting into one vent. The picture is not the best, however it looked like there should have been a better way of installing the venting system. Water heater #2 tees into the vent for water heater #1 runs a few feet where it makes a 180 degree turn, where it is picked up with a "y" into the main vent along with the heating unit. This just does not look right, although all three units vented properly.


Bob Harper
05-04-2008, 06:05 PM
"All three vented properly"???? Do you mean you test fired them and they did not backdraft or spill?

A 180 turn?
That manifold is propely sized for 205 mbtu?
Least flow resistance?
Properly supported?

Do you have any other pics Richard?

Markus Keller
05-05-2008, 05:30 AM
Ok, where to start?
- It looks like the HWT flues are larger than 4" (typical 40 gallon outlet). Have they been increased down below or is that the picture?
- Is the furnace draft induced or older atmospheric? That would be my primary concern. Furnace may need to be separated out.
- The TEE connections should also be a Y
- Did the flue suck out a match at the HWT hood?
- 200K+ into a 5", 6" main vent? Probably too much. (7 or 8") I know someone here has the chart and will post soon.

Richard Roshak
05-05-2008, 09:15 AM
Here are more photo's. Yes, all three units were properly venting when operating simultaneously.

Markus Keller
05-05-2008, 10:07 AM
That's a little better.
- The turn after the Tee connection should be changed to reduce resistance and provide better draft effect.
- Once you Tee units together into a run that run should be larger than the original individual runs because you are inputting more. Looks like it's the same 4"
- Even though the main is B-vent the insulation crammed around it isn't a good idea.
- From the looks of the sheetmetal I bet it's a newer induced draft furnace. Definite no-no having that hooked up on the run with the HWT's

Jerry Peck
05-05-2008, 10:16 AM
First thing I see is the lack of the required 12" vertical rise before making an elbow from vertical to go horizontal.

That in and of itself needs to be corrected, in which case it means taking that all apart and re-configuring it (properly this time - as would be done by a "competent" person).

Markus Keller
05-05-2008, 11:51 AM
Good catch Jerry, I forgot to add that in. Kind of dumb since I always right the crap out of 90's directly onto draft hoods.

Robert Dalga
05-05-2008, 03:03 PM
Also, gas hot water heater flues are typically Y'd into the chimney vent above the furnace flue.

Bob Harper
05-05-2008, 06:24 PM
Is that a 4" draft hood on WH#1? Anyway, manifold the two WHs together with as much vent rise straight up off the draft hoods first. Here's how you do it:
Run the B-vent (sized as a common vent for all three) into the basement according to the listed instructions. Remove that fire hazard insulation. Where is this B-vent going and how is it properly supported with that 90ell over the foundation wall? I doubt it is properly firestopped or supported with clearance.
If you use B-vent as a vent connector, you can run the connectors within an inch of the ceiling (but add a little for fudge factor). Otherwise, at least 6 inches below the ceiling. You can connect to the common vent two ways: one common manifold or WH manifold in above the furnace. Since the furnace is a CAt. I fan assisted 80% furnace, it too needs all the lift it can get. the run all vents 1/4"/ ft downhill. Need better support, too.

I would use one common manifold but..........when you connect draft hood equipped appliances to the furnace, you defect the primary safety controls ( vacuum switch and spill switches). You can have a 100% blocked B-vent up top and it will vent right out the WH draft hoods without tripping the safeties. Just did one last week. I'll post pics another time. What to do? Install spill switches on the WH draft hoods connected to the WH thermocouples. When they get tired of re-lighting the pilots, maybe they will change those two WHs for one power vented one out the side of the home.

This is a bad setup no matter how you vent it.