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Condensate termination


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Seems like most of the HVAC boys around here don't think there is a need for terminating the condensate drain above a P-trap for condensing furnaces. What are the problems of doing it this way?

Plus I was told that having a pan below upstairs furnaces was also good for propane in case is leaked gas it would flow down and out instead of into the walls, etc. Sounds good. Never heard that before.

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If that is actually connected to the drain it is wrong on many levels.

There must be an indirect connection. connecting directly to the sewer like that can leak methane into the house. Not as bad as an a/c condensate since it would not be in the environmental air, but still wrong. Also, that is an improper connection to the sewer line, not a fitting, just drilled into the line, maybe the plumbers among us can give you chapter and verse.

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Seems like most of the HVAC boys around here don't think there is a need for terminating the condensate drain above a P-trap for condensing furnaces. What are the problems of doing it this way?

Are you referring to the evaporator coil condensation or the condensation from the hi-eff furnace?

Plus I was told that having a pan below upstairs furnaces was also good for propane in case is leaked gas it would flow down and out instead of into the walls, etc. Sounds good. Never heard that before.

I've never heard of that either. Sounds like a myth.

Marc

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Because LP is heavier than air, you have to imagine it collecting in an invisible pool in the same places it would accumulate if it were water. California's mechanical code has an amendment requiring that LP gas storage and appliances not be arranged in such a way that gas can accumulate around them. In our basement, there is a large pan beneath the propane-fueled furnace. A duct from the pan goes to an exterior vent. Fortunately, it is a daylight basement and there was a way to run the duct with continuous downhill slope. I have seen some instances where a hole need to be bored from the basement to a downhill location, and others where it was just impractical to have a propane furnace in a basement.

Here is California's code text:

"303.8.1 Liquefied Petroleum Gas Appliances. [HCD 1 & HCD 2] Liquefied petroleum gas-burning appliances shall not be installed in a pit, basement, or similar location where heavier-than-air gas might collect. Appliances so fueled shall not be installed in an above-grade under-floor space or basement unless such location is provided with an approved means for removal of unburned gas."

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A friend of mine with too much money built a house on the shore of Lake Tahoe and ended up he couldn't place the furnace where he wanted below the house so he had to install 5 furnaces inside in closets, etc., because of that LP problem. Whoops. Like another friend of mine says, "The problems that millionaires have to put up with".

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OK, so by their logic, a trap on a propane furnace pan drain would be a bad thing.

So what happens when you pipe that drain into a methane source, the sewer line?

It is piped to open air. Being able to dissipate a propane leak to open atmosphere is the whole purpose of the rule. At my house, the duct is 16 inches by 14 inches and terminates on the building exterior. It prevents the possibility of an explosive concentration of LP in the basement. FWIW, ours is the largest such duct I have ever seen. Usually they are around 6 inches or so in diameter.

About 25 years ago, here in Marin County, someone succeeded in blowing up a house by turning on a propane bottle in the crawlspace with a lit candle on the mudsill. The propane filled the crawlspace and reached the candle. While the fire department called it arson, some folks referred to it as a rather creative divorce settlement.

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I see "gas drains" on LPG boilers and furnaces in crawl spaces around here. Generally there is a large sheet metal pan under the unit with a 4" ABS drain piped to the outside air. If the unit leaks gas it will pool in the pan and then start flowing out through the pipe.

A 4" drain would probably work fine for that purpose. A 3/4" drain would be next to useless.

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Thanks all. A vent for leaking propane gas then is obviously a large air vent large enough to not pose any restriction on the movement of the gas. In fact you would not want the furnace to be pulling combustion air in through the same pipe, so you would want air coming in from another vent.

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  • 1 month later...

First of all I see no P-Trap. If this unit has negative air flow at the evaporator it must have a P-Trap to keep the sewage gas from getting sucked into the air handler.

If the unit is of the Trane/American Standard make TAM7 or TAM5 then it is a positive pressure unit and does not need a P-Trap as its always pushing air down the drain.

Either way it needs what is called an AirGap where it ties into the sewage line and depending on what version of the IMC your state uses you may not be able to pipe it to the vent line like that you will need to run the 3/4 line down to a drain level where the vent starts.

The air gap cannot be installed by the HVAC contractor it must be installed by a plumber!

The first 18ft of the condensate line must be insulated with rubbertex to keep it from sweating if its located in a unconditioned space in the home.

If the unit is located in the attic it should have a drip pan below it with a emergency drain line connected to a separate AirGap from the air handler drain. The pan should also have a over flow switch to shut the unit down in the event both drains get clogged so that it don't over flow into the attic.

Sam

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