question from HO that I can't answer

Guy_6

The actual benefit of condensing is the extra transfer of heat gained BY condensing. Just as your body sweating transfers the heat off of you, the condensation in the boiler transfers more of the heat INTO the water. You have high heat from the burner washing over the condensed water, therefore evaporating it. IF the HO seems to have more "steam" out the exhaust, it means that his boiler is condensing more, and therefore operating more efficiently.
They are probably operating at lower temps, or have a higher mass SYSTEM aiding the condensing.

Leo G_99

Had a home owner today

ask if his Munchie 199M was working properly. I asked why he felt that there may be a problem? "well these boilers are supposed to condense the water vapour out of the exhaust fumes right? Then why is there so much steam coming from the vent?"

I had to tell him that I would have to try to get some answers from the Wall. Hopefully he comes here also, to see some of your theories!

Any reasonable answer would be highly appreciated!

TIA

Leo G

R. Kalia_10

I'm a homeowner, and even I know that. The HO says he has "so much steam", but how does he know how much is too much?

It's impossible for the exhaust to be perfectly dry; it has some moisture, and when it is cold outside, that moisture will condense into visible steam immediately. Probably only a few % of the moisture is leaving with the exhaust, but it looks like a lot because it is steam and a little water can make a lot of steam.

Now of course maybe their system is not condensing properly, for example, maybe outdoor reset is not functioning? One way to test is to collect the condensate for a day rather than let it be pumped away, and also monitor how much gas is used that day. Unfortunately I don't have the number for how many gallons of condensate (max) should collect per therm used, but it's out there on the web somewhere. They won't collect the maximum number, but they should get at least 75% of it.

Weezbo

chuck shaw would be the guy to ask...

couple days ago though while eaves dropping on the conversation next to me in class ...i heard it said that 1 gallon for every 100k BTu's burned,at 30 degree delta T between stack and return temp,... so something up to 2 gallons an hour might be somewhere in the ball park. later on in class Ed the instructor basically repeated the same thing in his presentation of the condensing boilers from Buderus.

oh, steam is invisible.

Brad White_118

Sounds normal...

If you did not see "steam" coming out of the exhaust flue, that would be much more of a concern.

Empire_2

I agree W. Brad

After all water vapor is a product of complete combustion.

Mike T.

Perry_2

Here is what I have observed with my Vitodens 200

In normal heating operation - I rarely ever notice any steam (and only a whisp at times).

However, during DHW production the Vitodens fires at a much higher rate and it is always noticable... A virtual cloud of steam blowing from the exhaust vent. Of course, at 100% firing rate the boiler does not condense as effectively.

It would not surprise me if other manufactures models do the same.

Perry

Aidan (UK)

Steam

Answer; it isn't steam.

Steam only exists at more than 100 degC at atmospheric pressure and it is invisible. The fact that he can see it tells him that it is at less than the boiling point.

It is tiny droplets of water vapour suspended in the flue gas stream, similar to fog. It evaporates into the air or it drops out of suspension when the gas velocity drops off.

You don't usually see the steam coming from non-condensing boilers' flues.

John Ketterman

Actually, Aidan(UK) has answered it better than I did. Quite possibly the HO was saying "I have more steam than other people do", or "I have more steam now than in my old system". In that case the answer is, noncondensing systems release hot flue gases, in which the water vapor is invisible. Condensing boilers cool the gas to extract the water, so the little water vapor still left in them becomes visible as fine droplets immediately upon hitting the colder outside air.

D107

Given other threads I've seen here about poorly set up and piped

Munchkins and other mod cons--assuming this was installed by someone other than you--perhaps the homeowner is willing to pay you a consult to check out his system. Maybe his heating bills are higher than he expected or outdoor reset is not in place......

David (HO)

mp1969

Discharge Temperature

When the discharge temperature is hotter than the ambient temp. (or outside temp)you create condensation.Plus the byproducts of combustion can also contain moisture.

Even my power vent water heater does this.

MP 1969

Make Peace Your Passion!

clammy

personal note

From what i have seen concerning munchkins exhaust and what i have noticed is that at higher running temp (ex call for domestic hot water )that the boiler produces what looks like steam i believe it because of the higher flue outlet temps in my own experences i would have to agree on a few that i have out running at below 160 on design day with outdoor reset(about 140) there's not much what looks like steam exhausting but when she's running for the indirect there's a flume so i believe it has to do with the boilers water temp .Is this munchkin being used in a high temp application peace and good luck clammy

Fred Harwood_2

condensation

A condensing boiler still lets the combustion products leave the "condenser" at 100% relative humidity. If those products, in leaving the exhaust pipe, encounter still cooler surfaces, or air, it will drop still more moisture out of the gases, becoming visible. If the products encounter warmer surfaces, or air, the gases will be invisible, even hydrophilic, and pass unseen from the exhaust pipe.

Scott Gregg

Normal or better

I'm with Guy. That's what is supposed to happen but sometimes doesn't because the system is not set up to cause condensing (20* delta T) Sounds like it's done right and the fellow should be very happy.

Rodney Summers

exhaust plume

I have to agree with Clammy that the lower the return water temp the less "steam"/water vapor plume will be obvious. However M. Etherton is the authority in this area he has a factory approved GFX on the exhaust of his T50 plus the humidity is non existant in Colorado. What say ye Mark?