USSC Hotblast Question

[jeff_t]

I've got two 8" pipes hooked up for hot air. Do I need 8" pipe for return air? I'm asking only because I have a bunch of 6" vent pipe already that I have no use for.

Jeff

 

[begreen]

I'd use at least 10" for the return. 12" would be better.

 

[Duetech]

Some Hot Blast furnaces have furnace filter kits that have a "return" flange built into them. Ask your supplier for information on a filter kit...Cave2k

 

[jeff_t]

The filter kit has a 14x 18 opening. I had an old plenum laying around and made a collector for it. I've got enough for two 6" pipes.

 

[M1sterM]

The filter kit has a 14x 18 opening. I had an old plenum laying around and made a collector for it. I've got enough for two 6" pipes.

It's all about the cross-sectional area (mostly, but friction and resistance play a part as well). For simplicity's sake, let's just look at area to start. Area is calculated as pi x radius-squared. So 2 (8") pipes x 3.14 x 4"-squared (16") is 100.48 sq. inches. You need to have at least that much in the return, or you're just handicapping the furnace. 6-inch pipes are a little over 27 square inches in cross-section, so if you can fit 4 into your system as a return, you should be in decent shape.

 

[jeff_t]

I don't have that much 6 inch, so I guess I'll start with a couple of eights and see what happens. I was thinking about this while looking at my LP furnace and how much smaller the cold air return is than the plenum coming out.

 

[begreen]

Could be that the LP system is not all that well designed. It wouldn't be the first time.

 

[smokinj]

I've got two 8" pipes hooked up for hot air. Do I need 8" pipe for return air? I'm asking only because I have a bunch of 6" vent pipe already that I have no use for.

Jeff

I used Dual "8"s in my return so if your doing one return it should be 16in or better