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Old 01-22-2010, 08:16 PM   #1
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Boiler - Pex vs Copper - Heat Exchanger


This is a continuation of a separate thread regarding my boiler install plan.

I picked up a 114k boiler a few weeks ago and am planning on using it in conjunction with my forced air system. My plan is to install 2 12" x 24" heat exchangers in my supply trunk. (later I may do radiant floor heat under our kitchen floor which is tile.)

The heat exchangers have 1" copper connections.
The boiler has 1 1/2" supply/return copper lines and has a Gossett G30 circulation pump on it.

I purchased all the 1" PEX fittings, crimps and tool I would need to do the install....and then found out that 1" pex and 1" Copper are not the same size. Pex is OD and Copper is ID.

The Heat exchangers I am looking at using are rated for 120k btu each at maximum capacity....I only need about 45k out of each one. Unfortunately the manufacture doesnt list the specs for the exact unit I want in the following documnet

http://www.ctwoodfurnace.com/PDF/V10...r_logo_pg2.pdf


I am not too worried about the reduced flow to each exchanger since I dont need their full capacity. Where I am confused is how to plumb them in. Originally I was going to plumb them in a series, but now I dont think that is a wise idea from a GPM flow perspective.

if I wanted to plumb them parrallel, to take advantage of the existing circulator pump, how would I do that? I would always run both heat exchangers at the same time, so I dont need to "zone" them.

I figure having two separate 1" PEX loops off the boiler is better than a single 1" loop.

Even though the system is pressurized to 12 psi, that should make no difference on the GPM since it is an equal pressure on either side of the pump, right?
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Old 01-22-2010, 10:40 PM   #2
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Boiler - Pex vs Copper - Heat Exchanger


You just need 1 line to the coils. Tee the line just before the coils to feed each coil separately.

Thats a 100 series B&G circ. Same flow rates as a Taco 007. But, for the cost of the motor, or the bearing assembly if it goes out later. You could get a Taco 007 now, and have a 2 year warranty on it. Just something to think about.

1" pex will easily get you an 8GPM flow rate. Make sure you install balancing valves on the return of each coil.

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Old 01-22-2010, 10:47 PM   #3
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Boiler - Pex vs Copper - Heat Exchanger


Personally I would be a little leery of that boiler. Looks like it has been spilling flue gasses around the door. I wouldn't put it into service without having it thoroughly inspected.
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Old 01-23-2010, 12:00 AM   #4
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Boiler - Pex vs Copper - Heat Exchanger


Quote:
Originally Posted by SKIP4661 View Post
Personally I would be a little leery of that boiler. Looks like it has been spilling flue gasses around the door. I wouldn't put it into service without having it thoroughly inspected.
It will be getting a thorough cleaning before going live. The burner chamber hasnt been cleaned and is probably 70% plugged up with soot and other crap, causing the unit to not vent and heat properly.
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Last edited by AndrewF; 01-23-2010 at 12:07 AM.
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Old 01-23-2010, 12:02 AM   #5
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Boiler - Pex vs Copper - Heat Exchanger


Quote:
Originally Posted by beenthere View Post
You just need 1 line to the coils. Tee the line just before the coils to feed each coil separately.

Thats a 100 series B&G circ. Same flow rates as a Taco 007. But, for the cost of the motor, or the bearing assembly if it goes out later. You could get a Taco 007 now, and have a 2 year warranty on it. Just something to think about.

1" pex will easily get you an 8GPM flow rate. Make sure you install balancing valves on the return of each coil.
My thought was to T the line off of the 1 1/2" into two 1" lines up to the HE.

I'll have to do some research on balancing valves and how they work.

Since this is not going to be my primary heat source, I am ok if the B&G fails and I have to order a replacement and it takes a few days.
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Old 01-23-2010, 12:04 AM   #6
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Just run 1-1" pex line to the coils, and split at the coil. Unless you just gotta use up all that pex you bought.

Running 2 lines won't hurt. but you won't get much benefit if any.
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Old 01-23-2010, 12:09 AM   #7
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Boiler - Pex vs Copper - Heat Exchanger


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Originally Posted by beenthere View Post
Just run 1-1" pex line to the coils, and split at the coil. Unless you just gotta use up all that pex you bought.

Running 2 lines won't hurt. but you won't get much benefit if any.
I need 30' and the smallest spool is 100', so length wont be factor this time.

I would need to get 16 GPM through the 1" PEX up until the T, if I want 8 per exchanger, right?
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Old 01-23-2010, 12:13 AM   #8
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Yes.

But, you don't want to put 16 GPM through that boiler, since its too small for that GPM.

11GPM is all you want through it.
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Old 01-23-2010, 12:16 AM   #9
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Yes.

But, you don't want to put 16 GPM through that boiler, since its too small for that GPM.

11GPM is all you want through it.
Oh, I figured since it had a 1 1/2" in/out that it was rated for much higher GPM...so my concern was that it might not work right if I limited it to 8 GPM.
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Old 01-23-2010, 12:23 AM   #10
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At 114,000 BTU output. A 20 rise through the boiler is 11.4 GPM.
1 gallon per 10,000 BTUs output for a 20 rise.

16 GPM would only give you a 14 rise. Thats a bit low for that boiler(that would only have that rise on paper, in reality ir would be lower yet). And could cause problems with the boiler.

At 10GPM, you'll have about a 23 rise.

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