# how quickly can a furnace raise house temp 20F?

On Jan 29, 4:33 pm, snipped-for-privacy@snyder.on.ca wrote:

Mark may or may not reply to your inquiry but he is correct....that whole concept that
"by upping the flow of water to the point that it passes through too quickly to absorb the heat."
is bogus / wrong......some people in this news group are confusing heat (energy ) with temperature of flow.
I'll pose this question.....If you touch something hot (ie burn your finger) do you dribble water across it drop by drop to remove the heat or put it under the faucet with a gushing flow?
Does the quickly flowing water "pass over your finger too quickly" to cool it off? I say no..... I want a gushing flow.
Yes the gushing flow removes the heat quickly BUT the gushing flow has its temperature increased only slightly so someone feeling the flow after it goes over my finger would say "the flow passed too quickly to absorb the heat" ....but my burned finger says otherwise.
It's quite happy that all the heat has been removed.
My qualifications..... I'm an ME :)
To comment on the furnace discussion.......yes, faster air flow through the furnace will probably increase heat transfer from the furnace heat exchanger to the air flow BUT the temperature rise of the air across the heat exchanger might to too low, such that the exiting air is too cold (temperature wise) for instantaneous comfort.
Yes, eventually the house will reach the desired temp but during the heating process....air that is too cold for occupant comfort has been blown throughout the house. Not to mention the wind chill of low temperature air. :)
cheers Bob
cheers Bob
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wrote:

OK - I'll answer you. It is not "flowing through too fast to absorb the heat"hat causes the problem. It is the unrestricted flow does not force/allow full circulation, so some of the coolant does NOT flow fast enough (it stagnates in certain cooling passages on certain engines) so although the rad temperature is cold, CERTAIN parts of the engine DO overheat. You get local boiling, and the vapour pockets do not get scavenged out - so you get larger pockets - which causes the local overheating to get worse. So the engine overheats, causing valve problems (the "pockets" around the exhaust valves are one point where this has been an issue in the past) and detonation.
One example was the circa 1969? Olds 350 Rocket. If you towed a trailer it tended to overheat a bit unless you advanced the timing (late hot and lean school of emission control) - meaning Super gas was MANDATORY. Guys used to pull the 'stat, figuring that would help cool the engine. With the stat pulled you were GUARANTEED to get detonation, timing advanced or not - and even on premium. The rad didn't boil over any more (usually) but the engine was still suffering from overheating.
That's just one example that I can remember right off the top - there were many more.

Not confusing the two at all. Just going from years of experience, and knowlege of how engines actually function.

Your theory doesn't hold water.

I'm ME too!!!! Oh, you said AN ME. Well, I'm a certified automotive technician as well as a computer technician. No iron ring - but but lots of varied experience.

I think you got it right there. The house MIGHT heat up just as fast, over-all but the perceived heat would be a lot less - a "cold draft" instead of a "bit of heat". Could be the same number of BTUs or KCalories or whatever unit you want to use.

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Zootal wrote:

I guess i just assumed that anyone with any mechanical knowledge knew that. The water actually runs cooler, but the metal parts run hotter. Especially in the back of the heads on a v-8. The thermostat actually provides a necessary restriction even when wide open that is required to make the proper flow to the back end of the block. If you insist on running no 'stat, the it's best to just take the innards from one and install the outer ring.
steve
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On Tue, 27 Jan 2009 19:24:06 -0800, "Zootal"

On SOME cars, they actually WILL.
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So, me make sure I understand. According to what others are saying, the rate at which heat will transfer from a solid to a fluid is not just dependant on the difference in temp between the solid and fluid (delta T), but is also dependant on the speed at which the fluid flows past the solid? IOW, if the liquid is moving, heat transfers slower, and the faster the fluid moves, the slower the heat transfers, even if it means the fluid is coolder then it would be if it was moving slower. Therefore, the solid will be hotter and fluid colder if the fluid is moving? Is this decrease in efficiency linear on the speed of the fluid?
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x-no-archive:

Zoot, I think the basic fact that you are missing is that HEAT and TEMPERATURE are not the same thing.
Consider a candle flame has a very high temperature but not a lot of heat.
A ton of water at 90 deg F has a low temperature compared to the candle flame but the water has a lot more heat.
If you slow the airflow down through a furnace, the TEMPERATURE of the air will go up but the total amount of heat will go down a little.
If you speed up the airflow the temperature will go down, but the total amount of heat will go up.
Heat and temeprature are not the same thing.
Bubba, yes I'm an EE.
Mark
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Oh, no, I'm not missing it at all. Let's consider a simple example. Say we have a heating element with some heat source applied to one side of it (gas flame), and air flowing over the other end of this element. The question is, how can I get the maximal amount of energy to pass from the element to the air? The assumption is that the temperature of the house is dependant on 1) how much energy is passing from flame through element into air flowing past it and 2) how much energy is escaping through doors, windows, walls, etc. What we are interested is how much energy we are putting into the house, not how efficient the house is.
Let's first look at the side of the element in proximity to the flame. Assume that the gas flame is constant so that a constant amount of energy is available. How much of this energy is going into the element, and how much is going up the chimney? Simple physics tells us that the amount of energy that goes into the element is dependant on the difference between the temperature of the flame and the temperature of the element. If they are both the exact same temp, then all of the energy from the gas flame is going to go up the chimney and get vented outside. If the temp of the element is 10 degress lower then the flame, the a certain constant amount of energy is passing into the element. If it is 20 degrees colder, even more energy is passing into it and again this is a constant amount(we'll get to what is going on at the other end of the element in a bit).
The assumptions are that 1) The amount of energy going into the element is dependent on the difference between the temperature of the elemen and the temperature of the flame and 2) the energy going into the element is being dissapated at the other end and is going into the house.
Does it stand to reason therefore, that the lower the temperature of the element, the more energy is going from flame into the element, and therefore the more energy goes from the element into the house, and that the difference between the temp of the flame, which we assume for now is constant, and the temperature of the element, is a measure of the amount of energy going into the house?
I need agreement on this before I can go any further, otherwise I'm wasting my time and yours :)
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x-no-archive:

Yes I think we agree about that ( if I understand you correctly).
And the more airflow over the element from the blower, the __cooler__ it will be, and the __cooler__ the air will be and __more__ heat energy will be taken from the element and less will go up the chimmy.
That is what the other guys were saying, more air through the blower, = lower air temperature.
Bottom line:
more air through the blower = lower vent temperature but a little better efficency in the furnace.
It seems backwards that the air temperature is lower when the heat energy is higher but it is correct and goes back to the difference between temperature and heat energy. Mark
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That's not exactly what they were saying - they were saying the more air through the blower, the colder the house will be. I'm saying the more air through the blower, the warmer the house will be.
So riddle me this - if more airflow over the element means the element is cooler, then that means more energy is going into the house. So how can the house be colder if this is the case? Where did the energy go?
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I don't know for sure what "they" were saying.
I'm saying as you increase the air flow through the furnace, the "element" will be cooler, the air out of the furnace will be cooler, and MORE heat energy will go into the house and the house will be WARMER.
Looks like we agree after all.
Mark
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Yah - that was kinda my point from the beginning :)
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On Thu, 29 Jan 2009 12:35:38 -0800, "Zootal"

Holly shit! You and trader would get along great. I cant believe how far you have stretched your simple question. Bubba
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LOL! I had to, to make my point :)
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So, if you have a 50 hp motor turning at 30,000, how hot is the heated surface inside the heater? Real hot? Not very hot because of the blast of air going across it?
If you answered real hot, then how can that be with a blast of air going across it?
If you answerd not very hot, then were did the heat go?
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Whats an EE degree, is that something you just avoided. Here everyone goes for Bachelors, Masters, and Doctorates.
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On Wed, 28 Jan 2009 06:32:01 -0800 (PST), ransley

An EE is something way way out of your league. It is usually one step above a garbage collector. As for the other degrees, you couldnt afford them. Remember, you are too cheap. You dont even take showers because it cost to much to heat water. Bubba
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At Zero, what do you do, offer coupons on your undersized crap. Walmart elect heat !!!! Yea and you sell 95% efficent WH tanks you moron, they dont EXIST, mr Bubbatardcrapolaasbrainsimanimbicileretard, and more
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ransley ransley ransley high efficency furnaces are sized to maintain 70 degrees at zero degrees outside, unless the homeowner lives somewhere colder like alaska.......
the furnaces are ost efficent sized this way
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Of course, I meant Bubbas heat world
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On Wed, 28 Jan 2009 17:54:25 -0800 (PST), ransley

Still cant seem to grasp reality, eh ransley? I guess when you live in cinderella world, everything is different. Bubba
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