h2o-air heat exchanger installation

PostBy: dirvine96 On: Thu Oct 04, 2007 1:09 pm


That furnace appears to be a 120k btus unit. It has a 3 or 4 ton blower, which means its rated for 1200cfm or 1600cfm with a wet AC coil. My guess is that it is rated for 1600 cfm with 3/4 hp motor.

It appears to me that you have a hot water coil that is not sized properly. Raising the water temp will not take care of the problem if coil is undersized. When hot water coils are built they look at several factors. The fan first of all. ( at what static can the fan perform up to spec ) Total btu output, usually based on 180 degree water temp. There is big difference between coils that are designed for supply use and that are used on the return side of the fan. Available space. A hot water coil can built to fit in a 19 X 20 plenum.

I don't know how you picked this coil.

What I would have told the coil supplier is that I need a coil that will deliver about 90k btus (not sure exactly what your need is) the furnace should have put out a 90k. I have a residential furnace that has a 1600 cfm blower, My supply plenum is 19X20 and I what to operate my boiler at 180 degree at 0 degrees outside. Then that coil should do exactly what the propane furnace did provided the boiler is big enough.

I would double check and make sure you have a coil that will work. Having that big of an air flow drop when the coil is placed on the furnace would make me nervous.

Let me know how you make out.

PS I can give you names of a couple of coil rep if needed.

Stove/Furnace Make: Hitzer 82FA

PostBy: Bob On: Thu Oct 04, 2007 1:48 pm

dirvine96 wrote:Having that big of an air flow drop when the coil is placed on the furnace would make me nervous.

In my experience it is practically impossible to accurately gage air flow beyond "more" or "less" without instrumentation. The simple fact that air flow is reduced when the coil is installed really doesn't provide much useful information if the objective is to determine whether air flow is adequate. A reduction in air flow is expected. The amount of reduction in air flow is, at best, a very imprecise estimate.
Stoker Coal Boiler: AHS 130
Coal Size/Type: Pea/Anthracite

PostBy: coaledsweat On: Thu Oct 04, 2007 2:46 pm

I doubt the airflow was cut in half, it may be percieved as that because the coil has dampened the noise coming from the blower. Now that it is much quieter, it SOUNDS like less air but probably is only reduced 20-30% max.
Stoker Coal Boiler: Axeman Anderson 260M
Coal Size/Type: Pea

PostBy: e.alleg On: Thu Oct 04, 2007 3:30 pm

You have spent too much time worrying about this, in a month you will be grinning ear to ear. Smile

hehe I'm good at worrying, I have OCD a little bit.
Stove/Furnace Make: EFM
Stove/Furnace Model: 520