Gas and Oil Home Heating Furnaces - furnace exhaust and duct question

hello,

I have relocated the furnace in my basement, and am putting
on new insulated ducts (round flex duct).

I also am replacing the old metal exhaust vent, as it had rusted
out, and replacing the return air duct, as the furnace is now
relocted.

Here are my two questions:

1) the furnace is an 80% efficiency unit, so I guess I have to
use metal pipe for the exhaust. Do I have to use the double
wall (type b I think?) or single wall? I can't find anything in my
code (international mechanical code.)

2) where do I buy a 12 x 12 square duct for the return air?
also, where do I buy longer lengths of the exhaust pipe? (I
have a longish run to the chimney to vent.)

the stuff at my local big box joint looks like junk and is
short (longest a 5' piece of the type b pipe)

thanks for any help!

1) the furnace is an 80% efficiency unit,

You will be able to use the single wall in open air area. then you must use the B-Vent in area that you are near combustalble items. (Wall, sheetrook and roofing)

have relocated the furnace in my basement, and am putting on new insulated ducts (round flex duct).

From where to where? If this your main run from the furnace, I would not suggest using this.. these flex are known for cutting back on air flow.. use all metal pipe if all possible.

2) where do I buy a 12 x 12 square duct for the return air

That sounds pretty small return if this is the main ductwork?, and how many room are tied to it?

where do I buy longer lengths of the exhaust pipe?

What you said, (5') is the longest you're going to find.. They go from 6" to 5'

the stuff at my local big box joint looks like junk and is short

What store you looked at? What Home Depot has is the same stuff I used in the past when I was in the field, mater of fact, same brand.. They are all the same... B-Vent is B-vent. and are UL rated..

5' is the biggest your going to find anywhere.

thanks for the advice, certainly helps. a couple of follow up
questions:

for the single wall vent: I'm running through basement and
crawl space, so pipe is near wood. how far from wood does it need to be to use single wall?

I'll use the rigid ducts. no problem there.

i've calculated 12 x 12 based on the btu output of my
furnace. output = 58,000 btu x 2 square inches return
per 1000 btu = 116 square inches. 12 x 12 = 144 so
should be large enough. air returns from one room only.

the b vent at home despot is ok stuff, but the single
wall pipe is this split stuff you put together yourself.
looks like it will leak. want to get better stuff if possible.


again, thanks.

From what you say on the flue pipe check code there.Sounds like you have to use B vent pipe.Most of the time single wall vent has to be 18" or more from wood or walls CHECK code there.
12"X12" for cold air, dont sound good to me like Jay said ,it's to small Even on a furnace like that Ill bet it has a 16X20 filter rack. You dont say how many outlet runs you have on it.;) ED

Use the B vent in the crawl space.. Is this being tied to the old chimmey going up to the roof? Or where?

12 by 12 will work. but your going to have the "rush" sound of the air flow going though the duct work...


All single wall pipe are going to be the snap into shape type thing.. They do seal up when they are snapped in.

thanks for the advice. sounds like i'll use the b vent, as I
dont think I can get 18" away from the wood.

can I attach the vent for the hot water heater to this vent?
If I do, do I need to do anything special, like go up a vent
size? since the hot water heater vent goes to the same place,
does it need to be b vent also?

the chimney goes up through the roof, yes.

the furnace has a 8" x 24" rectangular opening for the return
air. I can hook up two return airs if necessary. Maybe I should
rethink the size. what would be the maximum size I can go to?

again, where can I buy larger square or round tube from? I
need something bigger for the return air(s).

the furnace has eight 6" diameter round outlets

thanks!