"steam" from chimney.

[warrenshudson]

Greetings. I live outside of detroit, mi. I notice that my neighbors natural gas water heaters that are vented with b-vent seem to give a fair sized cloud of "steam" if you will, on a cold morning. My 220,000 btu boiler that is venting into a clay flue 8x8 chimney does not cause any steam to be visible at all. It should be noted that my natural gas water heater vents into the same chimney. People with the 90+% furnaces have a huge cloud of steam coming from their furnace vents. My question is: what causes some people to have steam and others not?

[Bubba]

You have not been a good person so you get the "bad" steam. Try thinking/worrying about something a wee bit more important. Bubba

[zero]

If the stack is above or below approximately 250°F.

-zero

[Edwin Pawlowski]

I'm glad you put "steam" in parenthesis, because, as you already surmise it is not steam. To be picky, steam is invisible. It is a vapor and cannot be seen at all. What you are seeing is condensation that is now visible in the cold air.

When fuel is burned, there are products of combustion that are given of into the air. The type of products depends on the fuel. Could be ash, soot, smoke (that contains many compounds) and water. Propane and natural gas both contains some water. the water, of course will not burn but will be vaporized and later condensed (made visible) and that is what you are seeing. For the products of combustion to pass up that big cold clay chimney, some of the condensation will drop back down and dry up. some will exit and not be seen. High efficiency units are sending the water vapor out a shorter length of PVC and you see more of it.

[nospam]

What you see is not actually steam, but is a release, due to a bad connection, of leakage from the nuclear heater that is used in some new installations. Do not allow your children to go outside when it is visible, or for four hours afterwards.

Remove NOPSAM to email me. Please let me know if you have posted also.

[CL (dnoyeB) Gilbert]

Humidifiers?

[RP]

Let me correct your argument a bit. Firstly these are parentheses (). These are quotation marks '' " :)

The answer to the OP's question is that the RH of the output from the condensing furnace is 100%. It is at saturation, otherwise it wouldn't be a condensing furnace. The dew point temp OTOH is only slightly lower than the temperature of the gas. A drop of only a few degrees will cause further condensation of moisture out of the gas.

With the noncondensing furnace, however, the dew point is several degrees lower than the temp of the output gas, and by the time the flue gas temp drops sufficiently to reach dew point the water vapor within it has dispersed, mixing with the ambient air. IOW the RH has dropped simultaneously with the drop in temperature, and thus when the furnace is full up to speed no condensation can occur. Your last point BTW is completely incorrect; the high efficiency unit is sending *less* water vapor out. Even so, some of what it does send out condenses before it gets far from the outlet, again, because its dew point is much closer to its saturated temp than in the low efficiency unit output.

Richard Perry

[Edwin Pawlowski]

Duh!

Would they not both send out the same amount of vapor per ccf of gas burned? Your explanation is more detailed than mine though. Thanks.

[Bob]

Steam is a vapor, but it isn't invisible. Clouds and fog are a vapor, but they can be seen. What about the steam that come off of ice when the sun hits it?

[Larry Bud]

That's not steam. Steam IS invisible, otherwise it's not steam. It's mist, fog or water vapor, but it's not steam.

[Bob]

There are only three states, solid, liquid, and gas. Mist, fog, water vapor, and steam are all H2O in a gas state. Depending on their temperature and percent of concentration, they can all be seen.

[RP]

Well no, they wouldn't. The condensing furnace diverts some of the moisture content of the gas out the condensate line. Your welcome.

Richard Perry

[EXT]

You are wrong, natural gas and propane do NOT contain water or the pipes would have ice blocking the pipes where the water accumulates in cold weather. However both are hydrocarbons, they contain hydrogen and carbon. When burned with oxygen they form carbon dioxide and water (hydrogen oxide). It is this water vapour that you see condensing outside the furnace chimney or vent. This is the same process that forms condensation at your car's exhaust pipe or water dripping from the exhaust pipe and the con-trails that leave white streaks behind jet airplanes.

[RP]

Vapor in engineering terms designates a gaseous state of matter. In that state water exists as steam, and is invisible. Vapor in common terms designates a mixture of gas(es) and condensed droplets and/or other particulates. When you see water vapor rising from a pot of boiling water it is small condensed water droplets (water in a liquid state) that you see. The steam from which these condense is however invisible.

Richard Perry

[RP]

While you are technically correct, I just wanted to note that as I read it he implied exactly that, i.e. when he referred first to combustion byproducts. The statement "gas contains moisture" is subject to interpretation :) Take everything in context. One might call this

*latent moisture*. OTOH, there is some actual trace moisture present in the gas mixture even before combustion, so let's go ahead and dot some more i's while where at it. :) BTW, I have encountered frozen gas lines, FWIW. Not many, but a few.

Richard Perry

[RobertM]

Well, no. To be perfectly correct, it would be "you're welcome", contraction for "you are". "Your" is a possessive pronoun.

Bob

[RobertM]

Wouldn't that be dihydrogen oxide? Hydrogen Oxide would be HO. Water is H2O.

Bob

[Edwin Pawlowski]

Mist and fog are not gases. They are liquid.

[=?MACINTOSH?Q?=D0_Colonel_=D0?]

Stack temperature.

If your clay-lined stack is cool enough to condense the water vapor before it exits the chimney ÐÊno "steam." If their metal stacks are hot enough to keep the exhaust temperature above the dew point until it gets outside Ð then you have "steam."

(BTW, "steam" is an invisible gas. What you're seeing is water vapor...tiny droplets of liquid.)

[EXT]