Garage Unit Heater - Trap In B Vent

[Andrew Kolar]

Is this vent installation allowed? I can't find anything in the installation instructions that would specifically prohibit it, other than having to drill a hole in the trap to allow for condensate drainage.

http://i303.photobucket.com/albums/nn125/KolarPhotos/IMG_6643.jpg

[Jerry Peck]

Clarify which direction is "up" for the photo.

It could be wrong for various reasons, depending on which way is "up".

[Andrew Kolar]

Clarify which direction is "up" for the photo.

It could be wrong for various reasons, depending on which way is "up".

The photo is oriented correctly (top of the picture is up). The vent comes out of the unit heater horizontally, drops down to create the U shaped trap, and then runs up vertically through the ceiling and ultimately the roof.

[Dom D'Agostino]

Last time I looked at a B vent install guide, horizontal runs need 1/4 inch rise/ foot of run.

[Gary Burnett]

Was the installer a plumber????? In addition to Dom's answer I also thought it had to have a minimum 12" vertical connector before the horizontal (1/4" per foot) run.

[Jerry Peck]

A Type B gas vent should never, never, never, never go "down", and should, as the others have said, never be less than 1/4" per foot UP horizontal slope (which precludes "down").

I see why they did it:
- lack of planning (any planning)
- lack of PROPER planning (if one plans, one should an properly)
- not understanding gravity flow of heated air (heated air rises)
- that connector (bottom of Type B vent section?) projects down so far - and / or - the unit is so high ... there was not sufficient space to make a turn up.
- is it possible that furnace is not designed for B vent?

Looking up the MII (manufacturer's installation instructions) would answer all questions about that install.

[Andrew Kolar]

Sorry for the lack of information, but I was in a hurry earlier when I posted. I should mention that this is a unit heater in a garage with a power combustion exhaust fan, not gravity flow. The manufactures installations instructions specifically say that downward slope toward the exhaust end it is an OK installation on a horizontal run, Or that condensation drain can be installed at the low point of the exhaust vent. But I have never seen a trap created an exhaust vent like this before? I do have reason to believe that it was installed by a licensed HVAC contractor.

[Andrew Kolar]

MII: http://www.littlegreenhouse.com/resources/Sterling-GG-Manual.pdf

Starting on page 20 & 21

[Jerry Peck]

MII: http://www.littlegreenhouse.com/resources/Sterling-GG-Manual.pdf

Starting on page 20 & 21

Actually, start on page 16, then 17, finally ... look at the drawings on page 19.

See anything different?

[Andrew Kolar]

Actually, start on page 16, then 17, finally ... look at the drawings on page 19.

See anything different?

I did look through pages 16 and 17. If I am not mistaken we are dealing with category III, on pages 20 & 21. Figure 13A is what had me wondering if the vent can be installed downward, potentially with a condensate drain? Don't get me wrong, I do not like this installation which is the reason I brought it up. I am just trying to nail down specifically how it is not allowed.

[Andrew Kolar]

I did look through pages 16 and 17. If I am not mistaken we are dealing with category III, on pages 20 & 21. Figure 13A is what had me wondering if the vent can be installed downward, potentially with a condensate drain? Don't get me wrong, I do not like this installation which is the reason I brought it up. I am just trying to nail down specifically how it is not allowed.

I believe I was confused between Cat I and III, thinking that the power inducer / exhaust fan put it in Cat III.

[Dan Hagman]

Andy, not allowed based on the vent connector needs a 1/4" rise per foot, I would have them raise the B-Vent as high as they can, install a B-Vent "T" cap the bottom and install the vent connector in the side of the "T" that will give the vent connector a small rise. The single wall vent connector still needs a 6" clearance to combustibles so if that is not possible they can install a piece of sheet metal above the vent connector with a 1" air gap and that should work or lower the unit heater!
They could eliminate the single wall vent connector and install all B-Vent in to the side of the "T", the B-Vent has a 1" clearance to combustibles.

[Andrew Kolar]

Thanks guys. I was confident it was wrong, but wanted to be able to intelligently explain why.

[Jerry Peck]

I believe I was confused between Cat I and III, thinking that the power inducer / exhaust fan put it in Cat III.

Power venting creates positive pressure in the vent and Type B gas vent is for negative pressure.

Question to others - is "fan-assisted' considered as creating "positive pressure" and thus Type B gas vent is not permitted?

[Gary Burnett]

My answer is NO! It is an inducer to remove any combustible gasses from around the heat exchanger prior to lighting the furnace.