View Full Version : VENTING one GHT into another ?

11-06-2008, 07:04 PM
I will be installing 2 gas heaters side by side, one supplying the lower level and the other the upper.

Either one or both will require a 4" vent pipe.
The 4" vent pipe from the furthest tank will be just about 4 feet long to the chimney.

I was thinking of venting the other tank (which will have a 3" or 4" vent pipe, depending on the tank I get) to the 4" vent of the first tank. It will be an almost a straight up connection 7" to 9" long from the draft hood into the that 4" vent.

Is it ok to do this? And are there any ready-made 4" T's that I can use for this?

11-06-2008, 08:41 PM
You have to spec. the btu rating of the two items and look at the charts in the National Fuel Gas Code book to see what flue will be required

11-06-2008, 09:06 PM
Aren't those standards more applicable to "power" vented exausts?

Both tanks will be "atmospheric venting". One will be 50,000 BTU's and the other either 50,000 or 40,000 depending on venting requirements.

11-07-2008, 04:04 AM
If you don't know how to do the job and don't understand how the National Fuel Gas Code is applied, do you think hiring a plumber would be a good idea?

I like it when my family wakes up in the morning!

11-07-2008, 05:09 AM
You cannot connect two 4", or even a 3" and a 4", to a single 4" stack. Usually the merged one has to have the same area as the total of the two individual stacks.

11-07-2008, 05:57 AM
Aren't those standards more applicable to "power" vented exausts? These specs are crucial for proper operation of a gravity vent. Inadequate draft leads to poor performance, and CO!

Both tanks will be "atmospheric venting". One will be 50,000 BTU's and the other either 50,000 or 40,000 depending on venting requirements.

A 4" B-vent with a total vent height of 15' will support 88,000 BTU . You right on the cusp. If the vent height is lower, the number goes down.. If the vent is higher, the number goes up.

In my condo, we have a 4" B-vent stack that supports a water heater on the first floor and picks up the 2nd fl. water heater as well. Both WH were probably 36,000 BTU original, and the replacements are 40,000. The vent height is approx 24', so we are OK.

11-07-2008, 09:05 AM
Let me clarify the setup a bit.

The 4" vent pipe will be coming UP about 15" from the first WH, making a 90-degree turn and venting into the brick chimney 4 feet away. The 4-foot connection will be sloped 1" to the chimney (1/4" per foot).

The second water heater is closer to the chimney and it's vent pipe (3" or 4") will be coming straight up for few inches and connecting via a "T" to the 4" pipe that vents into the chimney.

The chimney itself is at least 20"x30" and 28 to 30 feet high.
I know, ideally, it would be best to connect the venting separately. Unfortunately, there are obstructions in the way that will make it almost impossible to do so.

That's why I'm wondering if in this particular set up, with a large and high chimney and only a 4 foot vent run to it, I can piggy back the second short vent run to it.

11-07-2008, 08:08 PM
Are you asking if you should do it, or if it is okay for you to do it? I would not do it nor suggest that you do it, but then I have a built in liability if it did it. If you really want to do it, regardless of what we recommend, then go ahead, we won't care, and hope not to read about you in the papers or see you on the 6:00 news.

11-07-2008, 09:23 PM
It's so nice to wake up in the morning!:D

11-07-2008, 10:32 PM
HA HA funny :D

Thanks for all your advice... I decided to install two 40K BTU tanks with 3" vent pipes installed properly and separately.