Venting question

[Marc M]

I ran across a Payne HZ N/G furnace in a crawlspace that vented roughly 25 feet horizontally (correct rise) with (2) 30 degree elbows and then up vertically from a 90 elbow.
Question: This just seems somewhat excessive considering the elbows and total lenght. Is there a booster of some sort to help with the venting due to it's location? Is there such a thing? Or am I thinking too much into this?

Thanks
Marc

[Rod Butler]

Marc,

I am not familiar with the model number of the furnace. But as long as the horizontal portion is sloped at 2% plus (up) and the length is less than 75% of the vertical rise portion, you are ok.

In fact as I recall if the horizontal portion of the vent is insulated it can be up to 100% of the vertical portion.

Someone better help me with that last part, I pulled it from memory and mine has slipped from time to time. :confused:

HTH

[A.D. Miller]

http://www.docs.hvacpartners.com/idc/groups/public/documents/techlit/ss-pg8m-02.pdf

http://www.duravent.com/docs/instruct/L204A_July09.pdf

[Marc M]

Helps thanks...

[Dan Legner]

The 75% rule would apply if the lateral vent connector is single wall piple. However, since it's in the crawl which is likely an unconditioned space, the lateral venting should be double wall vent ( B vent). And double wall can go up to 100%. So if the lateral is 25ft. the total height from the furnace to the roof vent cap must be at least 25 ft.