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Old 11-06-2011, 03:56 PM   #1
ManCave
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Default DIY Water to Air Heat Exchanger

Hi guys,

I have an outdoor wood boiler Iím going to use to heat a pole building. I was going to install two 220,000 BTU Heat Exchangers and hang them in opposite corners. Well, classic boiler wants $800 each for them.

Have any of you made one from say a truck radiator? Are their better radiators that can be found that are reasonable or free?
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Old 11-06-2011, 04:36 PM   #2
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Default Re: DIY Water to Air Heat Exchanger

I have one for an attached that is just a heater core. A friend of mine is using truck radiators as a temporary setup but could be made nicer if it were to be staying.

Before I had mine infloor heat I used an old steam unit heater for heat. We had to choke the flow back to get the maximum heat differential. Use an IR gun on your in and out plumbing. You will need to experiment.
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Old 11-06-2011, 04:44 PM   #3
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Default Re: DIY Water to Air Heat Exchanger

get a old heater core out of the back of a school bus. they used to be good heaters back in the days,kept the back of the bus warm,
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Old 11-06-2011, 06:59 PM   #4
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Default Re: DIY Water to Air Heat Exchanger

Check your local building supply stores and HVAC centers for copper finned pipe and make your own.

http://2.imimg.com/data2/FW/JY/HELLO...es-250x250.gif
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Old 11-07-2011, 12:42 PM   #5
kbs2244
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Default Re: DIY Water to Air Heat Exchanger

You would not be the first to use a radiator.
It is, after all, what they are designed to do.
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Old 11-07-2011, 09:28 PM   #6
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Default Re: DIY Water to Air Heat Exchanger

One caution. Keep in mind that you can economize on the air side and end up costing yourself a pile of in electrical operating costs. You can take so much hp to drive the air that if the pressure drop across your coil is great, your electrical bill will be too. I cannot say that a radiator or other suggestions will not work well, just be aware of the dark side.

The example I would offer is the original condensing gas furnaces. You'd sell and install one a a couple months later get the "good news, bad news" call from the customer. What is the good news? " the good news is I reduced my gas bill by 20%". Gee that is great! What is the bad news? "The bad news is my electric bill went up 40%"! the early units went from a 1/4-1/3 hp motor to 1/2 etc. Keep yours eyes open
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Old 11-07-2011, 11:02 PM   #7
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Default Re: DIY Water to Air Heat Exchanger

Quote:
Originally Posted by Jackfre View Post
One caution. Keep in mind that you can economize on the air side and end up costing yourself a pile of in electrical operating costs. You can take so much hp to drive the air that if the pressure drop across your coil is great, your electrical bill will be too. I cannot say that a radiator or other suggestions will not work well, just be aware of the dark side.

The example I would offer is the original condensing gas furnaces. You'd sell and install one a a couple months later get the "good news, bad news" call from the customer. What is the good news? " the good news is I reduced my gas bill by 20%". Gee that is great! What is the bad news? "The bad news is my electric bill went up 40%"! the early units went from a 1/4-1/3 hp motor to 1/2 etc. Keep yours eyes open
Never thought about that. Thanks. I will do some looking around and see if maybe I can't find some options...
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Old 11-17-2011, 04:29 PM   #8
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Default Re: DIY Water to Air Heat Exchanger

friend of mine uses an old combine radiator and has a thermostat wired to a regular box fan.
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Old 11-17-2011, 05:34 PM   #9
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Default Re: DIY Water to Air Heat Exchanger

I actually just got back from the boiler store. I was going to break down and spend the $600 for a 140K unit but the ones they have in stock have squirrel cage motors which necessitate a fairly long transition between the coil and the motor. I don't like the looks of them at all. One could say they are butt ugly. Decided I may just buy the coil and then build the rest of the unit myself. I have a 48" finger brake and a spot welder so I guess I can save a lot of money doing it this way, too.

I need to find out how many CFM that squirrel cage puts out and then compare it to a normal fan and make a decision. Not sure why they use squirrel cages -- if it has to do with the CFM or noise.
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Old 11-17-2011, 08:21 PM   #10
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Default Re: DIY Water to Air Heat Exchanger

we use squirrel cage fans or centrifugal because of cfm in relation to the size of a blade fan would be huge.
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Old 11-24-2011, 11:03 AM   #11
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Default Re: DIY Water to Air Heat Exchanger

I'm looking at installing a Modine Style water to air heat exchanger but I'm too cheap to want to buy a unit. I don't want to jack your thread but I think we're asking the same thing.

I've found a couple of designs on Ebay, one uses a squirrel cage and the other uses a standard fan.












I've purchases a 16" x 16" heat exchanger that's rated at 119,000 btu's.



I've also purchased a 12" exhaust fan like in the 3 pictures above but I mocked it up and found the resistance is so great thru the heat exchanger that most of the air is blowing back thru the side of the fan and not going thru it. I guess that's the benefit of the squirrel cage blower, that air has no other place to go. I have picked up a small used squirrel cage from a local heating contractor.

Has anyone build one of these unit and have any pics or advice to share? I also would like to not have the heat exchanger and squirrel cage hanging from my ceiling if possible. (would like a smaller, more compact unit) I'm no engineer but I feel I have the ability to build one of these units.

I've also seen on the the nepacrossroads site (coal burning site) where someone used a squirrel cage and exchanger and built a box and placed it on the floor.



Any advive would be greatly appreciated!!
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Old 11-24-2011, 11:04 AM   #12
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Default Re: DIY Water to Air Heat Exchanger

Quote:
Originally Posted by Full Throttle View Post
we use squirrel cage fans or centrifugal because of cfm in relation to the size of a blade fan would be huge.
Could you explain what you mean by a centrifugal fan?

Thanks
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Old 11-24-2011, 11:33 AM   #13
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Default Re: DIY Water to Air Heat Exchanger

HIG,

Glad you joined the discussion!

With the exhaust fan you need to put a shroud around the blade and block off the back of the radiator so that air directed through the fan can only go through the radiator. I fly and have done a lot of reading on ducted fans that are used by both aircraft and hovercraft -- that shroud will actually make the fan more efficient. One thing though -- all fans are not created equal. Most fans are designed for free-air use. For our purposes, the fan has to be rated for a load. Otherwise, when its under load pushing air through the radiator the fan will burn up or have a much shortened lifespan.

When they give the BTU rating for those radiators they seem to be rated figuring about 16 gpm flow through the radiator. Most boiler pumps won't flow that much through a 1" pex. For that reason, I'm looking at radiators more in the 22x22 to 24x24 range. If they're rated around 200k BTUs you might actually get more like 140k - 160K. I've found those radiators for about $250 but many of the places are currently out of stock. I suspect they all buy from the same place in China.

As far as hanging one in my shop, I really like the 2nd design you posted (I looked at that one a couple days ago). The models with the squirrel cage are rather ugly. I was thinking if I go squirrel cage I would build an outer box so that its rectangle shaped and then put an inlet air filter (from a home furnace) in the back to keep from picking up crud in the shop and blowing it through the radiator.
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Old 11-24-2011, 06:32 PM   #14
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Default Re: DIY Water to Air Heat Exchanger

Quote:
Originally Posted by ManCave View Post
HIG,

When they give the BTU rating for those radiators they seem to be rated figuring about 16 gpm flow through the radiator. Most boiler pumps won't flow that much through a 1" pex. For that reason, I'm looking at radiators more in the 22x22 to 24x24 range. If they're rated around 200k BTUs you might actually get more like 140k - 160K. I've found those radiators for about $250 but many of the places are currently out of stock. I suspect they all buy from the same place in China.
Check out this web site starting at page 25 of their catalog, they have a nice charts showing the different sizes, GPM & CFM - it might help when determining a size.

http://www.altheatsupply.com/media/u...s/13-32bbb.pdf
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Old 11-26-2011, 03:20 PM   #15
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Default Re: DIY Water to Air Heat Exchanger

Quote:
Originally Posted by ManCave View Post
HIG,

With the exhaust fan you need to put a shroud around the blade and block off the back of the radiator so that air directed through the fan can only go through the radiator. I fly and have done a lot of reading on ducted fans that are used by both aircraft and hovercraft -- that shroud will actually make the fan more efficient. One thing though -- all fans are not created equal. Most fans are designed for free-air use. For our purposes, the fan has to be rated for a load. Otherwise, when its under load pushing air through the radiator the fan will burn up or have a much shortened lifespan.
Have you speced out any fan motors, how much do they cost?
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Old 11-26-2011, 04:31 PM   #16
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Default Re: DIY Water to Air Heat Exchanger

Go to ebaymotors and type in "aluminum radiator", you'll come up with about 20,000 choices in heat exchangers with and without fans and shrouds.
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Old 11-27-2011, 01:49 PM   #17
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Default Re: DIY Water to Air Heat Exchanger

i removed a heat pump and air handler from a friends house, the rad/core in the air handler looks like it could work well for a hot water heating system, maybe just use a complete air handler and run hot water through it, blower and all.
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