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Old 01-07-2010, 10:40 PM   #16
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Indoor Boiler Question


Why must it fit in a 10X24 duct?

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Old 01-07-2010, 10:52 PM   #17
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What if I put the heat exchanger between the AH and the supply trunk? There isnt much room there, but would that be an ok spot?

I still have my turning vanes above it....it would put it within about 2" of the resistant heat coil packs.
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Old 01-07-2010, 10:53 PM   #18
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Originally Posted by beenthere View Post
Why must it fit in a 10X24 duct?
Because you indicated it should be after the HP A coil in the air handler....

The A coil is on the bottom of the unit and the fan above it, and above the fan, the 20kw electric heat.

As you can see in the above photo, my supply trunk which goes left and right, is 10" x 24"

THis is an upflow setup. Air comes in from the bottom and exits out the top.
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Old 01-07-2010, 10:58 PM   #19
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You get the coil made to fit your duct work.
The coil can be bigger then the duct, was my point.
because the ends of the coil would restrict air flow if inside the duct.
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Old 01-07-2010, 11:05 PM   #20
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I understand.

THank you.
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Old 01-07-2010, 11:13 PM   #21
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Almost forget.
York makes a hydro coil that sits on top of the air handler. Just don't know if you have enough room.
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Old 01-10-2010, 09:14 AM   #22
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Any idea how close the heat exchanger coil could be to my 20kw e-heat?

http://www.houseneeds.com/shop/Heati...oilerstech.asp

The E-heat will basically be "disconnected" because the boiler is taking its place. I might even take it out and put it back in the box to help with my static pressure....but if I didnt, I'd wire it to W3 on my t-stat and configure the t-stat to never use it unless I manually energize it.
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Old 01-10-2010, 09:40 AM   #23
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20 KW of strip is 68,260 BTUs.

As you see, hydro coils are very restrictive to air flow.

Take the 18X18C3.5 coil. At 1500 CFM, it has a .24”wc PD.
If you were to use that coil with only 1000CFM of air flow going through it. Its PD would only be .105"wc.

Hydro coils need to be selected for both the BTU you need, and the PD your system can overcome.

And often. A large BTU coil is preferable to use at a lower PD. Then a smaller higher rated PD one rated for the lower BTU you need.
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Old 01-10-2010, 09:53 AM   #24
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You lost me there.

If I was willing to live with putting a larger hydro coil in front of the A Coil in the 20x25 drop down box, that would be better to my airflow and WC then a smaller 12x12 on the supply side, right?

Also, the air output on the AH is about a 12x12 opening....because of the way it was made with the heat coil slot...you can see one off the panel that limit the width to 12" instead of the full width of the AH (23")

I could put a 12x20 coil in the blue area of the first photo pretty easily.
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Last edited by AndrewF; 01-10-2010 at 09:56 AM.
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Old 01-10-2010, 10:16 AM   #25
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I was refering to using 2 coils on the supply side. One for each supply trunk.

For a single coil. You would need the 22X25X3.5, rated at 2700 CFM and a PD of .32"wc.
Because when the air flow is only 2000CFM through it. Its PD would only be .18"wc.

If your air flow is less then 2000CFM through it. Its PD will be even lower.
But. As the air flow drops, the air temp coing from it will increase. And your back to harming your blower motor.

Next. What about refrigerant migration. With the coil heating up the air that is being blown over the coil. You will cause liquid refrigerant migration. And could cause oil problems with your heat pump.

Putting a hydro coil before the indoor coil is a real bad idea. Could cost you more in repairs then you save on your heating bill.

Put the larger coil on top of your air handler. And slant the transition as much as you can.

Or use 2 coils as I suggested earlier. And you'll get better air flow.

Before the coil can be put in. You still need to get your Static pressure down lower. Or you'll end up not being able to use the heat pump for heating or cooling no matter what the outdoor temp is.
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Old 01-10-2010, 11:29 AM   #26
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Would frigerant migration be less of a concern if my HP has a crankcase heater?

The manufacture PDF says :
Crankcase heater (where indicated)


Why dont I hear concern with oil migration on a standard A/C system that is after say a fuel oil or LP furnace? Does it have anything to do with the reversing valve?
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Old 01-10-2010, 11:55 AM   #27
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I did find a manufacture that sells 12" x 24" unit and is rated at 124,000 BTU.

Wouldnt that restrict my airflow on each side of the supply trunk at an angle too much?
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Old 01-10-2010, 12:31 PM   #28
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Because an A/C doesn't run in the winter.
It gets restarted in the spring on a warm day. A heat pump will be required to run again on a cold day.
Crack case heater will help keep oil and refrigerant from being mixed in the crank case. But not in the outdoor coil.

Whats the PD of the 12X24 coil you found.

2 large coils one in/at each supply trunk will have less then 1 big coil with all the air going through it.

The 18X18's i posted about. Would only add.105" PD.

Will the 12X24 you found add less?
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Old 01-10-2010, 12:45 PM   #29
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Adding boiler coils is out of my league but why not increase the supply duct size to fit the larger coils then back down to trunk size instead of dinking around with slanting it?
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Old 01-10-2010, 12:55 PM   #30
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He doesn't have a lot of room between his air handler and the trunk line.
Already has an air flow problem.

The hydro coil will compound his air flow problem.

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