Dryer venting

[Bob Elliott]

Had a brain freeze moment on if it is ok to vent a gas dryer down and wondered why that would be ok when it is not ok to vent a mid -efficiency furnace that way?

[Gordon I. Kay]

Cat I or mid efficient furnaces operate with a fan assist that is designed to over come the resistance of the burner and heat exchanger only and have a non positive vent static pressure.
Residential clothes driers have a positve vent pressure, much like down flow venting on a gas jenn aire range. The venting for a clothes drier is also defined as a moisture exhaust duct.

[Bob Elliott]

I figured that was the case.
Dryers also need to push solids so would naturally have more power, though they have smaller BTU output.

[Richard A. Hetzel]

Furnace venting: manufacturer's written instructions, period. Deviate from them, and one risks a code violation and a voided warranty. If they say the vent can go down, it can, If they don't say it, it can't.

[Bob Elliott]

Originally Posted by Richard A. Hetzel

Furnace venting: manufacturer's written instructions, period. Deviate from them, and one risks a code violation and a voided warranty. If they say the vent can go down, it can, If they don't say it, it can't.

Hi Rich
You got it backwards.

I was just wondering why it is ok to vent a dryer downhill.
Never saw a mid -efficient vented down or allowed.
Have you ever seen any that were ok to vent that way?

[Richard A. Hetzel]

No, I can't recall ever seeing a furnace vented downwards on purpose. I have seen a couple with vents pitched slightly downward due to...umm...less than perfect workmanship.

My own dryer vents downward. The louver to the outside was installed just above floor level, for some reason. It has functioned perfectly for five years that way.

But backwards??? Mr. Elliott, PLEASE! =)

[Bob Elliott]

What I meant was that I already know Furnace flue vents must go up by at least 1/4 inch per foot but wondered why not need for dryer vents.
Since mid-efficiency models follow the same 1/4 inch rule as far as I know I was wondering what the difference was.

Now I know.