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Old 01-13-2010, 08:38 PM   #61
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You may have a hard time finding a company that knows how to check static pressure.
Hmmph! You mean every HVAC guy doesnt know how?

Oh yeah, that is what got me into this HVAC DIY project in the first place....

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Old 01-13-2010, 08:40 PM   #62
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This should work too, right?

http://cgi.ebay.com/Gas-LPG-Manifold...item5ad63e602b
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Old 01-13-2010, 08:47 PM   #63
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If your heart isn't set on digital then a magnahelix might be cheaper. Mine was $80 or so.
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Old 01-20-2010, 09:53 PM   #64
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Hpex is fine.
With that boiler, you MUST use Hpex. If you use a pex without an oxygen barrier. You will have a internally rusted up boiler. that clogs your water lines.
Why must I use pex with an oxygen barrier?
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Old 01-20-2010, 09:56 PM   #65
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To prevent rust. Which will clog up everything.
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Old 01-20-2010, 10:25 PM   #66
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To prevent rust. Which will clog up everything.
So oxygen barrier PEX pipe keeps O2 from soaking into the water?

I thought one just mixed in glycol or something to keep that from happening, no?
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Old 01-20-2010, 10:36 PM   #67
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No. Glycol prevents freezing or pipe bursting. And also decreases heat transfer rate. In other words, raises heating or cooling bill, depending on system type.
But nothing to prevent oxygen from being drawn into the water through non oxygen barrier pex.

Water likes to absorb oxygen.
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Old 01-23-2010, 11:01 PM   #68
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THis product should work, right?

http://www.h-a-s.com/literature/Hydr...cification.pdf


Engineering Specification:
Tubing shall be a 5-layer barrier PEX tubing approved for radiant heating and potable water applications.

Hydro-Flex PEX-AL-PEX Multi-Layered Composite Pipe 1" x 100'consists of an overlapped welded aluminum core with an inner of and outer layer cross linked polyethylene. The inner welded layer of aluminum makes Hydro-Flex PEX-AL-PEX 100% oxygen tight, providing longer life for heating system components.
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Old 01-23-2010, 11:30 PM   #69
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Yep. that will work.
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Old 01-24-2010, 08:18 AM   #70
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So I've talked to a number of vendors who sell heat exchangers, they recommend using the 12x18 HE and blocking off the 6" that the HE wont cover.

Since I have 12 - 6" supply take offs on the right side, I think that is fine.

I am more concerned for trunk that goes left of my AH, it has 15 - 6" supply takeoffs.

Although based on this chart (see pdf), an 18x12 trunk is rated for 1100 CFM.

So maybe it is ok if I get 12x18 HE and stick in each supply trunk, they would be within 6" of the AH blower....thoughts?

Or I could get the 12x24 unit and stick it on top of the AH before it connects to my 10x24 trunks.
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Old 01-24-2010, 09:05 AM   #71
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How much PD will that coil have at the air flow you need in each trunk.
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Old 01-24-2010, 09:23 AM   #72
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How much PD will that coil have at the air flow you need in each trunk.
I dont know yet, I asked the vendor for the manufacture specs on their unit that size.
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Old 01-24-2010, 09:26 AM   #73
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The main idea of using those larger coils earlier was to minimize PD and get/keep your air flow up.
Next, using those 2 larger coils. You also decrease the temp your boiler water needs to be. Saves a little money on oil.
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Old 01-24-2010, 12:24 PM   #74
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The 12x24 has the same as a 16x18.

.257 at 1500 CFM and;
.274 at 1693 CFM.

My AH runs around 1700 CFM from the last heat rise test I did.

As for the 12x18, i dont have an answer on its specs yet.

A 12x12 at 1016 CFM has .195
A 12x12 at 900 CFM has .185

So the .274 single unit has a lower WC than two 12x12s do...so why not save on plumbing and HE costs and just install the 12x24 at the takeoff and remove the 20KW heat coils (iirc, they add .2 WC)
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Old 01-24-2010, 12:35 PM   #75
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The 12X24 at 1693 would only have a .1"wc PD
And at 900CFM it would only have a .08"wc PD.

If you use the 16X18 and have transitions made(no dead heading/blocking open duct space, creates turbulence that increases PD).
Then you make you blower work easier.

You can remove your strip heaters either way, and make your blower work easier.
But keep them handy. In another 2 years or so. Oil will be 4 bucks plus a gallon again.

If you want to use only 1 coil, thats fine. But, mounted at the air handler, it generally takes a coil designed for that mount to keep the PD down. Custom coils are seldom made with the turbulence between the coil and air handler in mind.

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