BTU Efficiencies...

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Chuck the Canuck

Chuck the Canuck

Feeling the Heat
Oct 10, 2012
416
Keswick Ridge, New Brunswick, Canada
Howdy ya'll. So as I mentioned in a previous post, the pot I was boiling on top of my wood stove for humidity control crapped out last week (handle fell off and spilled water all over the place and made a mess yada yada yada), so I went out today and bought a nice big 16 quart stock pot with a heavy duty steel reinforced bottom on it as a replacement. But once I got home I got thinking (that's usually when the trouble starts).

So the temp outside is around -26C (-15F) and the heat pump is struggling to keep the house at 20C (68F) without the auxiliary heat kicking in (read as baseboard heat on steroids, watch dollar bills flying out windows) and I just want to get the stove good and hot to take some of the load off the heat pump. And this makes me think, now if I go and plonk this big piece of steel full of water on top of the stove, isn't it going to be absorbing all sorts of thermal energy and basically rob me and the house of critical BTU's that could be heating up the house, just when I need them most???? !!!

Anybody ever think of this?

PS, the pot still sitting on the coffee table, and the stove is cranking out some much needed heat at the moment.....
 

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And this makes me think, now if I go and plonk this big piece of steel full of water on top of the stove, isn't it going to be absorbing all sorts of thermal energy and basically rob me and the house of critical BTU's that could be heating up the house, just when I need them most???? !!!

You are correct though eventually you will get some of the heat back from the warm water and pot. Heat transfer deal,thermodynamics. It's science!
 
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I would say don't sweat the small stuff. Though, you probably are correct :)
 
It doesn't matter where in the room you place the container of water, it's going to be warmed by the heat from the stove, just like everything else in the room. If you want the water to get real hot, put it on the stove. If you don't need it above general room temp, leave it on the coffee table. I seriously doubt that having the pot on the stove from the get-go is somehow "robbing" your room of BTU's. But don't let my 3 degrees in Mechanical Engineering (emphasis on Thermodynamics/Heat Transfer/Fluid Flow) influence you. Rick
 
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We have a small one on ours..wife swears by it,I swear when she spills a little water filling it...not really,I know better..lol.
Yeah,just put it on the stove..I'm sure the diff is not measurable.
 
fossil said:
It doesn't matter where in the room you place the container of water, it's going to be warmed by the heat from the stove, just like everything else in the room. If you want the water to get real hot, put it on the stove. If you don't need it above general room temp, leave it on the coffee table. I seriously doubt that having the pot on the stove from the get-go is somehow "robbing" your room of BTU's. But don't let my 3 degrees in Mechanical Engineering (emphasis on Thermodynamics/Heat Transfer/Fluid Flow) influence you. Rick
Click to expand...

Fossil, do you live in MN by chance... We're looking for a good Thermal/ Fluid guy. PM me if you have any interest and I'll give you more details.

As far as robbing heat is concerned, I agree that you won't be able to detect the heat difference, but would you loose the energy used to evaporate the water (latent heat of condensation). Am I missing something?
 
Badger said:
As far as robbing heat is concerned, I agree that you won't be able to detect the heat difference, but would you loose the energy used to evaporate the water (latent heat of condensation). Am I missing something?
Click to expand...

Ok, the wife was right again.... that's alright, I'm getting used to it. It doesn't matter anyway, because the house is now up to 22C, the heat pump is in sleep mode, and I'm heading downstairs to put the pot on the stove.... :)

Cheers,
 
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Badger said:
...the energy used to evaporate the water (latent heat of condensation)...
Click to expand...

That would be Latent Heat of Vaporization, and since the resulting steam presumably hangs around in the room until eventually coming to rest on a cooler surface, it'll give that up as Latent Heat of Condensation, so that's pretty much a wash. Besides, we're talking about (really) so little water here it's pretty insignificant when you consider that the stove heat is going toward raising the temperature of the whole room and everything in it. Where you put the water is about as important as where you let your dog lie down. I live in Oregon, I'm retired, but I'm flattered. Rick
 
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Really though. A proper humidifier would do a much better job if your R/H is low.
 
So far as I'm concerned, the only use for a pot of water on top of a wood stove is to put potpourri or scented oil or cinnamon sticks, or whatever in to produce a nice scent in the home. It will never produce enough airborne water vapor to significantly raise the humidity unless you live in a walk-in closet.
 
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HotCoals said:
Really though. A proper humidifier would do a much better job if your R/H is low.
Click to expand...

Well, perhaps, but it would require electricity to operate, and I don't want to pay NB Power anything more than I have to. And the other thing is, I've been here for 8 years and this is the first time ever (using the pot on the wood stove) that the house has been properly and comfortably humidified (my nose hasn't bled once, and I haven't been shocked by touching anything etc...). But, deep down, just beyond my recalcitrant reptilian brain stem, I know you're right. But I'm gonna stick with the pot for now..... ;)
 
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fossil said:
So far as I'm concerned, the only use for a pot of water on top of a wood stove is to put potpourri or scented oil or cinnamon sticks, or whatever in to produce a nice scent in the home. It will never produce enough airborne water vapor to significantly raise the humidity unless you live in a walk-in closet.
Click to expand...


I tried using a small humidifier in my stove room for a week and didn't change the humidity at all. I put it back away.
 
Chuck the Canuck said:
Well, perhaps, but it would require electricity to operate, and I don't want to pay NB Power anything more than I have to. And the other thing is, I've been here for 8 years and this is the first time ever (using the pot on the wood stove) that the house has been properly and comfortably humidified (my nose hasn't bled once, and I haven't been shocked by touching anything etc...). But, deep down, just beyond my recalcitrant reptilian brain stem, I know you're right. But I'm gonna stick with the pot for now..... ;)
Click to expand...

Sounds good to me!

My house is to large for the two quart deal to amount to anything. That said I think she just likes to keep a eye on it and to feel like she is helping.
Also she agrees with you 100% about paying the extra coin to run the humidifier..lol.
 
However, that pot of hot water is just the ticket for this:

swissmiss.jpg
 
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Badger said:
I tried using a small humidifier in my stove room for a week and didn't change the humidity at all. I put it back away.
Click to expand...
Did you put water in it?
How small is small?
Joking!
 
Chuck the Canuck said:
isn't it going to be absorbing all sorts of thermal energy and basically rob me and the house of critical BTU's...
Click to expand...

You could say the same thing of anything else in the room (or even the mass of the stove if it's thick soapstone or more of a masonry heater). When you build a fire in a cold room, the air warms quickly and the non-air contents of the room warms slowly (except the stove itself). But the more stuff in the room, the more that stuff also COOLS more slowly than the air after the fire dies. Your pot of water is just part of the thermal mass of the room contents... rather than rob heat, it simply borrows it and then gives it back. You don't need to worry about losing heat to things within the room, only to walls and windows and floors and chimneys and things that help transfer heat out of the room.
 
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Badger said:
I tried using a small humidifier in my stove room for a week and didn't change the humidity at all. I put it back away.
Click to expand...

I have a small one that claims 3.5 gal output a day, but never runs through more than a gallon. I can put 2-3 gallons a day into the air with a single pot on the stove.
 
branchburner said:
I can put 2-3 gallons a day into the air with a single pot on the stove.
Click to expand...

Yeah, the pot on the stove rules for putting moisture into the air....
 
OK, here's the physics. Heat (energy) is transferred to the pot and is then transferred both to the water and to the room, radiating from the pot. But where does the heat (energy) go? Into your room!! The water vaporizes and air with a higher humidity always feels warmer to skin than dry air. Reverse is also true in that cold moist air feels colder than cold dry air. Reason? Moisture helps transfer heat (energy) better than air, which is a terrific insulator if it's not moving.
OK, back to the heat. Whenever energy is transferred, it must always be an equal equation. So heat loss from stove must equal heat gain to pot + water + room. IOW, you lost nothing.
I will remit my invoice forthwith. lol

BTW, since you are from NB, put some cider in the pot and the room will smell very nice plus you have hot cider to drink, plus it adds moisture to the room. Wow, triple bonus.
 
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branchburner said:
rather than rob heat, it simply borrows it and then gives it back. You don't need to worry about losing heat to things within the room, only to walls and windows and floors and chimneys and things that help transfer heat out of the room.
Click to expand...

Thanks branch, your explanation really cleared it up for me, and I appreciate it! :)

Cheers,
 
DougA said:
Moisture helps transfer heat (energy) better than air,
Click to expand...

So in fact I shoulda put the freakin pot on the stove first thing instead of arsin around thinkin about it to death!!!
 
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DougA said:
BTW, since you are from NB, put some cider in the pot and the room will smell very nice plus you have hot cider to drink, plus it adds moisture to the room. Wow, triple bonus.
Click to expand...

LOL
 
Badger said:
What, no one told me to put water in it. Sounds like a conspiracy to me!
Click to expand...
I'm just waiting for someone to post about drying wet wood next to the stove..that must add moisture to the room also. lol
That comes up now and then . Well stove is set for the next 12 hours and I'm out!
 
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