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Vent condensate freeze (C) Daniel FriedmanCondensing Boilers & Furnace Condensate Drains

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High efficiency & condensing heating boiler condensate drainage piping & disposal guide:

Plumbing & heating codes & suggestions for disposal of condensate produced by high efficiency gas-fueled condensing boilers & furnaces.

This article series discusses the installation, operation & maintenance as well as defect inspections for high efficiency oil and gas fired heating boilers & furnaces, condensing boilers, and similar energy-saving equipment.

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Condensate Drain Specifications for High Efficiency & Condensing Gas Heating Equipment

High efficiency heater problems (C) Daniel Friedman

Reader Question: proper piping materials for condensate from condensing furnaces or boilers

2017/01/11 Greig said:

Can a brass fitting be used to connect a condensing boiler flue condensate or will this corrode?

This question and answer were posted originally at CHIMNEY WET TIME & CORROSION

Reply: use corrosion-resistant piping for condensate disposal

Condensate from condensing boilers is quite corrosive, a view shared by experts (Xinqiao 2006). That's why plastic is a good drain material. Stainless steel might be acceptable in some situations. I'd be careful about using brass, iron, copper, galvanized pipe.

While the manufacturer of the boiler would be the an authority on what is acceptable piping material for condensate disposal, model building codes say this, using ICC model building codes adopted by Virginia in the U.S. as an example:

SECTION 314 - CONDENSATE DISPOSAL

[M] 314.1 Fuel-burning appliances. Liquid combustion byproducts of condensing appliances shall be collected and discharged to an approved plumbing fixture or disposal area in accordance with the manufacturer’s installation instructions.

Condensate piping shall be of approved corrosion-resistant material and shall not be smaller than the drain connection on the appliance.

Such piping shall maintain a minimum horizontal slope in the direction of discharge of not less than 1/8 unit vertical in 12 units horizontal (1-percent slope).

[M] 314.2.1 Condensate disposal. Condensate from all cooling coils and evaporators shall be conveyed from the drain pan outlet to an approved place of disposal.

Condensate shall not discharge into a street, alley or other areas so as to cause a nuisance.

[M] 314.2.2 Drain pipe materials and sizes. Components of the condensate disposal system shall be cast iron, galvanized steel, copper, cross-linked polyethylene, polybutylene, polyethylene, ABS, CPVC, or PVC pipe or tubing. All components shall be selected for the pressure and temperature rating of the installation.

Condensate waste and drain line size shall not be less than 3/4-inch (19 mm) internal diameter and shall not decrease in size from the drain pan connection to the place of condensate disposal.

Where the drain pipes from more than one unit are manifolded together for condensate drainage, the pipe or tubing shall be sized in accordance with an approved method.

All horizontal sections of drain piping shall be installed in uniform alignment at a uniform slope.

Research on corrosion in condensing boiler condensate systems

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Reader Comments, Questions & Answers About The Article Above

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2020/03/31 common sources of condensate leak in high efficiency or condensing gas heating equipment

Leaks at a condensing gas boiler or furnace - where is the leak source? (C) InspectApedia.com TimTim

You ask why, in a condensing or high efficiency gas furnace, we see condensate dripping back into the heater.

[Annotations on photo are by InspectApedia.com - Ed.]

[Click to enlarge any image]

You cite condensate at the combustion air intake - which IMO is a bit unusual except for heaters that use a concentric air-intake + exhaust-outlet system.

Can you confirm how your heater gets its intake air and how its exahust is vented? Can you post a photo of the air inlet and exhaust outlet from outside the building (one photo per comment).

Please also post more detailed photos of the point where you think the leak is occurring.

You also pose the most-common explanations: improper pitch somewhere in the exhaust vent system, and improper exhaust vent termination (blocked, too close to ground, wind-impaired).

You also mention inadequate return air which is a clever and subtle potential explanation of exhaust vent problems: if there is inadequate return air it is possible that a vacuum is created near

*either* the combustion air intake (creating for gas fired appliances a high risk of unsafe carbon monoxide production)

*and/or* a vacuum near the exhaust vent that on gravity-vented or naturally-vented appliances draws exhaust gases out into the space around the heater

*or* for high-efficiency gas appliances, a nearby negative air pressure might draw condensate (and a small amount of exhaust gas) out of a small diameter drain opening or air intake or poorl-sealed flue joint where it could drip into the gas heater.

On a high efficiency gas appliance condensate may be disposed-of by draining back into a condensate drain for disposal into the building's DWV system. Condensate may also drip out of the exhaust termination but in freezing climates I've found this to be unsafe as ice build-up can block the exhaust.

See details at

DIRECT VENT INSTALLATION, SNAFUS & SPECS

and

CONDENSING BOILER/FURNACE CONDENSATE DRAIN

also

CLEARANCE REQUIREMENTS for Direct Vented Gas Appliances

SLOPE REQUIREMENTS

On gas heaters that I've inspected and that had rust stains inside of the cabinet the most-common leak was at a gasket or joint on the exhaust line that was allowing condensate to escape into the unit instead of draining into the condensate drain that some units carry.

Following all of that speculation and review where are we?

We need a thorough, complete, detailed visual inspection of your specific gas heater by an experienced technician. In my experience a careful inspection (rarely some testing is needed) can find visual evidence of the leak source (by deposits if not actual condensate) by some common sense: water flows down-hill. Find the stains, look up and around to find the source.

I'd like to see more-detailed photos of the leak stains in your heater and of the components above and near that location.

2020/03/31 Tim said - Why does moisture sometimes come from the combustion air intake line on furnace

So, I’m unable to get an answer from anyone on this.

Why does moisture sometimes come from the combustion air intake line on furnace & cause rust & corrosion. It could be improper pitch, not enough return air, exterior terminations are to close to home...but nobody has a definitive answer. Any thoughts?

This Q&A were posted originally at HEATING SYSTEMS

On 2020-01-14 - by (mod) - black mold has been entering the Condensate Pump

Sounds like some kind of slime mold. It would be useful to track backwards to try to find the source. I suspect that you're going to want to clean and sanitize the system.

On 2020-01-14 by Rick

High Effficiency Condensing furnace 11 years old. In this last year, a black mold has been entering the Condensate Pump to the point of smothering it.

Replaced the pump and discharge line this Dec 16, 2019. Pump ran clear and in the last week, Algae again blackening the discharge line and is evident in pump reservoir. Pump discharges into laundry pump drain.

On 2019-07-24 - by (mod) -

That should be ok - be sure water drains away from the building not into it.

On 2019-07-24 by Chuck Goin

can I dispose of condensate from a gas fired furnace to the lawn area?

On 2018-11-15 by Clinton Blake

How far away from a well should condensed water drain ?


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