Strange situation.

Help Support Plumbing Forums:

Solder

Member
Joined
Sep 27, 2019
Messages
12
Reaction score
1
Location
Mississauga
High-efficiency furnace creates exhaust that has condensation in it it's a product from the flue gas going through a secondary heat exchanger it's not created inside any cold pipe.
I'm not talking about this.

Condensation is also created in the exhaust pipe when it goes outside the house. The cold temperature outside makes the exhaust pipe cold. This is why there's a drain line at the end of the inducer motor and not before. This is also why the exhaust pipe must also be sloped downwards towards the furnace so the condensate makes it's way down the pipe and into the drain catch line at the neck of the inducer.
 

voletl

Well-Known Member
Joined
Dec 17, 2014
Messages
800
Reaction score
248
Location
New York
It seems you still want to talk about this so I'll continue the conversation.

I've installed high-efficiency furnaces in the middle of July in the middle of August where it is 100 + degrees outside and guess what we had to run them to test them to make sure that they were running efficiently and guess what would you believe it they made condensation and there was no way in hell that pipe was cold...... condensation is a natural product of combustion stop saying it's created because of a cold flue pipe.
 

TomFOhio

Professional
Professional
Joined
Jan 20, 2018
Messages
1,068
Reaction score
222
Location
Mansfield,, Ohio
That is why you have a drain on the side of a high effecient furnace going into a floor drain or pump. We did the same thing that
voletl did.
 

Solder

Member
Joined
Sep 27, 2019
Messages
12
Reaction score
1
Location
Mississauga
It seems you still want to talk about this so I'll continue the conversation.

I've installed high-efficiency furnaces in the middle of July in the middle of August where it is 100 + degrees outside and guess what we had to run them to test them to make sure that they were running efficiently and guess what would you believe it they made condensation and there was no way in hell that pipe was cold...... condensation is a natural product of combustion stop saying it's created because of a cold flue pipe.
The pipe is still colder than the exhaust gases.

Condensation also occurs in the exhaust pipe of cars. Ever seen water leak out of a muffler?
 

Diehard

Well-Known Member
Joined
Aug 19, 2017
Messages
2,566
Reaction score
445
Location
North Reading, Mass.
The temperature at which such condensation occurs is called the DEW POINT. Yes, it can be at any temperature. The dewpoint temperature is the temperature at which the air can no longer retain all of the water vapor which is mixed in it, so some of the water vapor condenses into water.
 

Solder

Member
Joined
Sep 27, 2019
Messages
12
Reaction score
1
Location
Mississauga
The temperature at which such condensation occurs is called the DEW POINT. Yes, it can be at any temperature. The dewpoint temperature is the temperature at which the air can no longer retain all of the water vapor which is mixed in it, so some of the water vapor condenses into water.
When air cools to its dew point through contact with a surface that is colder than the air, water will condense on the surface.
https://en.wikipedia.org/wiki/Dew_point
 

voletl

Well-Known Member
Joined
Dec 17, 2014
Messages
800
Reaction score
248
Location
New York
The pipe is still colder than the exhaust gases.

Condensation also occurs in the exhaust pipe of cars. Ever seen water leak out of a muffler?
Yes because condensation is a natural byproduct of combustion
what are you not understanding?
Condensation in combustion is not created when a hot gas touches a cold pipe. It is naturally occurring in combustion. I'll say it again it is naturally occurring in combustion.....
 

Jeff Handy

Pro Handyman, NOT A Pro Plumber
Joined
Jul 5, 2019
Messages
1,508
Reaction score
247
Location
Chicago suburbs
When natural gas (mostly comprised of methane) is burned, (combusted) it combines with oxygen to create water, but that water is in the form of water vapor, (gaseous form) not liquid water.

When the gaseous water vapor cools below its dew point, it will condense into liquid water.

Dew point will vary based on how concentrated and dense the water vapor is.
Very highly concentrated water vapor has a high dew point, and can condense into a liquid at higher temperatures.
But even cool, seemingly dry air has a dew point.
When temps drop low enough, any water vapor will become unstable and will condense out into liquid water.

There is no need for a cool pipe or other cool hard surface for gaseous water to turn into liquid water (rain, for example).
No pipes floating up there in the clouds.
If the concentration of water vapor is high enough, and ambient temperature is low enough, water vapor will be unstable and unable to remain in gaseous form.
So it turns into (condenses into) liquid water.

But if water vapor makes contact with a surface cool enough to lower its temperature to its dew point, it also becomes unstable, and will not be able to remain in vapor form, and will condense into liquid water.
 
Last edited:

voletl

Well-Known Member
Joined
Dec 17, 2014
Messages
800
Reaction score
248
Location
New York
I vote to change the name of this form to Plumbing form / science class so people can actually learn basic Elementary School science
 

FishScreener

Well-Known Member
Joined
Aug 23, 2018
Messages
328
Reaction score
92
Location
83467
Yes because condensation is a natural byproduct of combustion
what are you not understanding?
Condensation in combustion is not created when a hot gas touches a cold pipe. It is naturally occurring in combustion. I'll say it again it is naturally occurring in combustion.....
Water vapor is the chemical byproduct of the combustion. Condensation occurs when that vapor cools and changes state from a gas to a liquid. Cooler pipe walls will cause condensation if they are colder than the vapor to liquid transition temperature.
 

Wildthing

New Member
Joined
Jul 24, 2019
Messages
1
Reaction score
0
Location
Douglasville GA
I vote to change the name of this form to Plumbing form / science class so people can actually learn basic Elementary School science
I feel like I am back in school again. Main thing different now is that we have "Google". All very educational and entertaining.
 

frodo

Just call me Macgyver
Professional
Supporting Member
Joined
Sep 28, 2014
Messages
7,964
Reaction score
2,500
Location
right here right now, over there later on.
There are several reasons why water heater condensation occurs:

  • The flue gases are cooled below their "dew point" when having the cold air supply.
  • When the temperature of the water inside the tank drops below 110 F. Once the water inside the tank is heated above 115 F condensation should stop. It takes up to 2 hours for the water to heat up to the temperature where the condensation stops.
  • During the cold start-up of the brand-new unit.
  • An undersized gas heater.
  • The temperature setting is too low.
  • A large amount of hot water is used in a short time while the incoming water is very cold. Keep in mind that the cold incoming water during the winter time and periods of cold days might produce large amounts of condensate.
If you have one of the above situations that will cause the condensation, fix the problem by increasing the temperature of the incoming air, water or tank size. Proper, unobstructed venting is also important so the moisture can leave the heater easily. As the condensate is mildly acidic, and as it will corrode the steel vent, PVC and stainless steel vents are recommended, if applicable and required per code.

Problems associated with the water heater condensation:

  • The condensate can drip onto the burner causing the pilot outage
  • Corrosion on the metal surfaces
  • Puddle of water
Power Vent and Power Direct Vent heaters are equipped with the condensate drain, so the water vapor from the exhaust gases will roll down the PVC vent pipe and through the drain port out. The recommendation is to get a condensate drain kit for convenient draining, and metal drain pans to protect the room where the heater is installed.

long story short, a domestic flue type water heater should not condensate if it has been installed correctly and the temperature is set at a normal level --- 120 degrees
 

Latest posts

Group Builder
Top