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[Gunpowder]

I have a boiler that I hooked up to another building last year and am ready to run it to the house. Problem: I popped off the side of the plenum of my late '80's Williamson highboy and there is no room between the A coil and the top of the plenum before it heads down the horizontal distribution.

So does that mean I need to replace the furnace before tackling the boiler? It is a 350' run from boiler so I am already looking at the expense of the Thermopex. I am guessing I will need to put in a new furnace which these days are much smaller footprint for the btu. Then postpone the boiler run for a few years.

Old furnace so the upgrade is worthy but defeats the purpose of going to a woodboiler.

Hate to just run the 50KBTU secondary building with a CL6048. So much overkill.

[RSI]

Is there anywhere on the return side of the furnace that you can mount a heat exchanger? A furnace that old should not have anything in it that would be affected by the heat like some newer ones might.

If you are going 350' each way, I would not use 1" Thermopex. You will want pipe that is at least a full 1" ID.

[mlappin]

Can you go under the A coil? If not then like been suggested, place it in the return duct and let the furnace pull air thru it.

[shepherd boy]

 Can you lift the a-coil to give room under the a-coil for the water coil? You can lift an a-coil up into the horizontal duck if need be. If it is to the top of the horizontal duck your out of luck on supply side.

[mlappin]

I have a guy that will raise the a-coil for 50 bucks, I could do it myself, but he’s  a AC guy anyways, if he screws it up he can fix it.

Prefer it on the heat side of the furnace if at all possible, then the furnace can back feed heat to the boiler if required.

[Gunpowder]

Mr. Lappin and I have discussed the size before. I had a local dealer spec 1" Thermopex/Rahu. I called Central Boiler and the VP even said 1" unless there was slope involved. And he recommended the Taco Viridian pump.

Inlet is available but the size would be considerably smaller exchanger than the outlet. Top of acoil is almost to top of box. I might be able to squeeze the exchanger below it but my understanding is the exchanger always goes last and not closer than 12" due to chance of freezing.

[Gunpowder]

Can you go under the A coil? If not then like been suggested, place it in the return duct and let the furnace pull air thru it.

I know if it goes within 12" above ther is a chance of freezing. But you can install it directly underneath? I always read it has to go abover the A Coil.

[Smokeless]

Go with the Logstor full 1" inside dia. 1 deg heat loss /100'  It will pay for itself many times over.
Cost of electricity is more pumping water threw smaller pipe. 
We explain this several times a year on this sight.
Use a grundfos 26-99. 3 speed. Shoulder months run on Med. then when it gets cold switch to hi.

[mlappin]

Can you go under the A coil? If not then like been suggested, place it in the return duct and let the furnace pull air thru it.

 I always read it has to go abover the A Coil.

Why?

Order on mine is HX then a coil, but I have a bastardized setup, like four foot of duct between HX and A coil. Don’t ask, a bunch of free stuff my tin knocker Dad brought home from work years ago.

I could see where you wouldn’t want the A coil practically sitting on the HX, the drip tray could cause weird air flow patterns thru the HX.

[E Yoder]

Coils in the return are quite common, probably will work better starting and stopping flow to prevent convection up the cold air return.
If you want it to backfeed heat then you'll have to lift the AC coil or use two coils on the duct branches.
You could route the yellow wire to the compressor through a freeze protector sensor if you're concerned about freezing.

[Gunpowder]

Go with the Logstor full 1" inside dia. 1 deg heat loss /100'  It will pay for itself many times over.
Cost of electricity is more pumping water threw smaller pipe. 
We explain this several times a year on this sight.
Use a grundfos 26-99. 3 speed. Shoulder months run on Med. then when it gets cold switch to hi.

The new Taco Viridian pump is suppose to be 80% less electricity to run. Central Boiler said make sure to use it because of the cost benefits to use vs the older models.

Logstor is the only manufacturer of true 1" ID aren't they? I assume it is close to the 1" Thermopex vs 1 1/4?

[Gunpowder]

I might have room to raise the A Coil. there is about 5" above it to the top of the Plenum and 2" below it ti the base of the furnace box. That would be preferred to putting it in the return where the HX would have to be so tiny to fit. 

[shepherd boy]

 Just wondering the logic of why a coil will freeze if it's within 12" of the ac coil? Does the air warm that much in 12"? I've put a number of them within 1" above with on problem.

  Yes, raise it 4". That will give you 6". I've done many tight against but you'll have several inches for air space. I'd rather do that than in the return in an oil or gas furnace.

[Gunpowder]

I contacted another dealer who said 1" Logstar should work on my 350' run. Anyone have a link to an online calculator to look at the 3/4 (Thermopex) 1" (Logstar) and 1 1/4 (Logstor) calculations?

According to my math w/o just use of a calcualtor, at 350' and assuming 20 DT and a 100,000 BTU furnace (furnace is 100,000, HX is est 200,000 BTU). I used 100,000 in calculation.

1" Logstor  (using 1" pex table)= 43.89 head?
1 1/4 Logstor (Using 1 1/4 pex table)= 15.63 head?

[E Yoder]

I don't have Taco Viridian specs in front of me but the only way I'd think you'd get 100,000 btu's with that medium head pump on 1" is by running a large(ish) (like 40 degrees) delta T.
 The coil is oversized it sounds so it might work? At low flow you'd want to counterflow the coil. Obviously 1 1/4" would flow much easier.
That's just an estimate..