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Author Topic: Heat exchangers  (Read 13323 times)

ghitch75

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Re: Heat exchangers
« Reply #30 on: February 13, 2013, 07:03:02 PM »

yes filter is a must or the coil turns into the filter :thumbup:
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willieG

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Re: Heat exchangers
« Reply #31 on: February 14, 2013, 03:28:51 AM »

I never install in the plenum


I always try to install in the main trunk line supply

If that don't work I'll go to the return side and make a new filter space.

If you install in the supply side of the main line the air is already filtered
my mistake on referring to plenum...i also installed in the main feed trunk after the filter. just after the furnace itself (very sorry for error)
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automan77

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Re: Heat exchangers
« Reply #32 on: February 14, 2013, 05:01:01 AM »

I have a buddy that has a 18x20 in a 1,800 sq ft home. Would that be like 140,000 btu
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WoodMOJoe

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Re: Heat exchangers
« Reply #33 on: February 14, 2013, 08:00:27 AM »

Great thread here.

I (for some reason) had assumed that the heat exchanger needed to be in the plenum over the A-coil (upflow propane-fired)furnace).

That was going to be a difficult trick in my situation, installing it in the main trunk line will be a breeze.

I'm learning.   8)

Thanks!
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automan77

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Re: Heat exchangers
« Reply #34 on: February 14, 2013, 08:22:14 AM »

Who has the best price on a 12x18 heat exchanger
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Scott K
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Scott7m

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Re: Heat exchangers
« Reply #35 on: February 14, 2013, 08:58:25 AM »

I have a buddy that has a 18x20 in a 1,800 sq ft home. Would that be like 140,000 btu

No...  The numbers on the box are worthless

How can the manufacturer know how much water will be flowing through the coil?  They don't

Do they know if we installed 3/4" lines or 2" lines, they don't.   

What I'm saying is there is no way to determine what size coil you need by simply looking a a btu rating on the box.  I can take the same coil, put it in my system and get 60k btu an hour, take it to another stove, another system, and it make 110,000 btu an hour.....  Same coil, different system design
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willieG

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Re: Heat exchangers
« Reply #36 on: February 14, 2013, 10:48:02 AM »

the real pros can straighten me out here if i am wrong but here is something i always think and i could very well be wrong...so here goes

lets take your house and a water hose...you house us putting out 40 pounds pressure, you have a outside tap with a y on it..youhave a 50 foot garden hose on one side of the y and the other side shut off. you open the tap and lests say for fn you are getting 3 gpm out the hose....now you open the other side of the y with another 50 foot hose on it,,,because you have now given that 40 pounds pressure some where else to go so you have eased the head pressure  in the first hose and added head pressur in the second hose,,but you have likley reduced the velocity at which the water is moving so in fact it is moving slower but it will not be half or what it was so lets say now it could be moving 2 gp in each hose so now you have 4 gpm...i think a larger heat exchanger may do this as well...you are capable of moving say 6 gpm through an exchanger that has maybe 8 tubes but your pump is capable of 10..so you are pushing with the force of ten but due to friction you can only get 6 through the exchanger...add now, an exchanger with 16 tubes you are  adding length to the pipiing and you think it would add double the ehad but becasue you are lowering the velocity of the water the resistance is much lower so you get more gpm through the larger exchanger

the pros can step in and tell me if i am on the right track or not i  hope i am typing what i am thinking...lol
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Scott7m

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Re: Heat exchangers
« Reply #37 on: February 14, 2013, 10:57:16 AM »

I think the plate exchangers are more restrictive than the coils though, I know if u run 10 plates you have to be careful and keep the flow up
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Jd79

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Re: Heat exchangers
« Reply #38 on: March 02, 2014, 03:18:00 PM »

Quote
In heating, restrictions do not mean a whole lot, during heating the fan is run on medium speed unless heat source is a heat pump. Air conditioning and using heat pumps is where too much restrictions can cause problems. Coil flanges will make no difference in the operation of the original equipment, they wont cause enough restriction. HVAC systems should be designed off the cooling load. Its easier to heat a home than it is to cool it.

thats all good with gas and oil but electric air handlers with heat strips if you stick a water/air coil in the supply air it will burn the heat strips up from to much restriction and turbulence........i always put the coil in the return.....

Is this a big concern?  I've always noticed when my backup heat strips come on, the variable speed blower ramps up to high speed.  I never thought about the heat exchanger causing too much restriction that it could potentially burn out the backup strips if they did come on.  Can anyone elaborate more or have specific examples?  I know this is an old thread, but I've been trying to decide where to put my hx if/when we ever get this OWB built and I was pretty well set on placing it in the supply above my updraft air handler.  I have read that in the return ductwork, you risk overheating the blower and electronics in the air handler.  That's not really much of an option anyway due to space restrictions.  I don't think I could get an exchanger into my return ductwork anyway.  I've heard mention of using the main trunk line (after the furnace) but that would mean my heat exchanger would be put in the attic.  I suppose that's possible, but it would still create a restriction after the heat strips.  What sayeth the experts?
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Sloppy_Snood

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Re: Heat exchangers
« Reply #39 on: March 02, 2014, 03:55:51 PM »

I never install in the plenum

I always try to install in the main trunk line supply

If that don't work I'll go to the return side and make a new filter space.

If you install in the supply side of the main line the air is already filtered

I am thoroughly "corn-fused" here...  :bash:

Why is it that you don't install a water-to-air heat exchanger in the plenum of a home's existing forced air furnace?  :-\

What the heck is a "main feed trunk?"  Isn't that a plenum?  :-\
« Last Edit: March 02, 2014, 04:10:23 PM by Sloppy_Snood »
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Scott7m

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Re: Heat exchangers
« Reply #40 on: March 02, 2014, 04:25:40 PM »

I never install in the plenum

I always try to install in the main trunk line supply

If that don't work I'll go to the return side and make a new filter space.

If you install in the supply side of the main line the air is already filtered

I am thoroughly "corn-fused" here...  :bash:

Why is it that you don't install a water-to-air heat exchanger in the plenum of a home's existing forced air furnace?  :-\

What the heck is a "main feed trunk?"  Isn't that a plenum?  :-\

It's the main duct that comes out of the plenum where the fan itself is located.   I have no desire to mess with that big metal box that has very little space to work with when I can accomplish the same thing by installing in the duct board or main trunk line right above it.

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ffbare

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Re: Heat exchangers
« Reply #41 on: March 02, 2014, 08:08:45 PM »

 :post:
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mtoll

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Re: Heat exchangers
« Reply #42 on: March 03, 2014, 04:19:32 PM »

So does it really matter if the heat exchanger is above the furnace fan so the fan sucks air through it or below so it blows through the HE even if there is some small restriction below the fan 
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mlappin

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Re: Heat exchangers
« Reply #43 on: March 03, 2014, 04:36:31 PM »

So does it really matter if the heat exchanger is above the furnace fan so the fan sucks air through it or below so it blows through the HE even if there is some small restriction below the fan

If you pull air thru the HX then you might have the possibility of overheating the motor on the blower. Others that install for a living would know for sure.
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Scott7m

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Re: Heat exchangers
« Reply #44 on: March 03, 2014, 04:42:12 PM »

So does it really matter if the heat exchanger is above the furnace fan so the fan sucks air through it or below so it blows through the HE even if there is some small restriction below the fan

If you pull air thru the HX then you might have the possibility of overheating the motor on the blower. Others that install for a living would know for sure.

We have done a lot on return side and never seem it be an issue.

If you go to return side tho u must install a filter on upper side of coil or it will become the filter
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