drain lines

[hvacvegas]

Please explian why a vent is not needed before trap with a gas furnace below the e-coil.
I don't want to do this wrong

Most would agree you need a trap.

There is no need to have a vent BEFORE the trap.

There is only one reason I can think of installing a vent BEFORE a trap, and thats if some moron put a easy trap on a unit that is interally trapped.
IE: Climate master geothermal heat pumps are internally trapped. If an inspector can't get it through his head that the unit is trapped internally, and makes you install an external trap, then you would need a vent before the SECOND trap.

Having 2 traps in a drain line will create an air lock. This is why plumbing has a vent pipe.


If we are talking about a vent AFTER the trap, we're in a different ball game. Everytime I do an install with a drainline that goes from one floor to the next, and goes only knows what moron ran it, I'll install a vent AFTER the trap. This will prevent the airlock. I'll make sure the top of the vent is higher than the coil pan, or is within the secondary pan.

The downside to installing a vent BEFORE the trap, on a standard gas furnace/ac installation, is that your dumping cold and hot air into the furnace room. Doesn't sound that bad, but your customer WILL complain about it.

If you install a vent before the trap on a air handler, your now allowing the air handler to suck water back into the coil. It won't drain.

[brian.nc]

I agree totally about the air handler.
I was mainly concerned with installations of gas furnaces in the charlotte area where they are primarily in the attics and unfortunately with static pressures around .9-1 inch w.c.

That static is way too high but just about all of the duct work is the some here. To overcome that static we would a trap about a mile deep.

With a furnace on its side and no room for a deep trap what can be done?

[CraziFuzzy]

to overcome a 1 in water column static pressure.. you would require a trap > 1 in deep (providing... a 1 in column of water). There would be no difference in a trap at the evap than a trap at the furnace... I guess I don't understand the confusion.

[hvacvegas]

I agree totally about the air handler.
I was mainly concerned with installations of gas furnaces in the charlotte area where they are primarily in the attics and unfortunately with static pressures around .9-1 inch w.c.

That static is way too high but just about all of the duct work is the some here. To overcome that static we would a trap about a mile deep.

With a furnace on its side and no room for a deep trap what can be done?

1" static isn't "way to high". It's high. But not insanely high.
I put a furnace/ac in a house last year, had a 1.3", normal easy trap. No problem draining. Fixed ductwork after we got the air on .

If you have a gas furnace in an attic, then you diffenetly don't want a vent before the trap, because now your dumping conditioned air out of the house.

For proper operation, you don't need a trap on a furnace/ac.
Although alot of codes require it.