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[gmviso]

I have a forced air upflow furnace, Does it matter whether the heat exchanger from my boiler goes above or below the A/C coil in my plenum?

[Ridgekid]

It should go down stream of your furnace fan. This way your drawing cooler air into the fan, BEFORE it picks up the heat from the HTX.

[RSI]

I have a forced air upflow furnace, Does it matter whether the heat exchanger from my boiler goes above or below the A/C coil in my plenum?

Depends on who you ask. Some OWB manufactures say below but I prefer above. Their reasoning is so it won't freeze. The major flaw in that is that a properly working AC system runs above the freezing point and if it is low on freon it can get colder but will then ice up. That condensation running off the A coil and out the drain would freeze way before the water in the heat exchanger.

Then assuming it does ice up and get cold enough to freeze, the ice will block off the airflow and the cold will go down.

This is just my theory on what would happen but mine has been pretty much setting right on top of the A coil and has never been drained.

If you are worried about it just put a drain on it and drain the water for the summer.


So, in other words, no, it makes no difference. 

[gmviso]

Thanks for the good info!

[BIGDIESEL20S]

Well I was kinda wandering the same thing about where to put my heat exchanger. I planed on putting it in above the forced air unit in the supply (after fan and ac coil). But after doin some asking around a lot of guys that put these things in around here put them in the return (before ac coil and fan). I didnt want to do this because it seems to me that would be vary hard on the fan having to work under that kind of heat. Unfortunate for me, my house has a finished basement and the forced air furnace is stuck vary tightly in a corner and I dont have room to install my heat exchanger in the supply. So for now I'm putting it in the return and hoping for the best.

[Ridgekid]

Although I did not install my HTX, I asked the same question-Why not below the ac coil?

My dealer said it's for Two reasons:
1. The heat load on the fan motor.
2. And it needed to be Downstream or the air filter.

Pic:
http://outdoorwoodfurnaceinfo.com/forum/index.php?action=media;sa=media;in=30;preview

With that being said, what we didn't discuss was 24/7/365 operation of the OWB. (Do I could heat Domestic water) He said If I wanted to do that I would need to put a bypass line on the Furnace HTX, otherwise I would be heating the air that was just cooled by the AC coil. In short, we decided not to operate the OWB 24/7/365.

BTW- The picture is of our upflow furnace. (air handler)

[gmviso]

So are you heating your DHW just in the winter months or not at all? If you already heat your DHW but just during the winter, you could add a 3-way manual valve or a 3-way electrically operated zone valve at your water heater. Fairly straight forward install I think. I am just in the planning and acquisition stages but do plan to heat my DHW year round.

[Ridgekid]

gmviso- Nope, just heating domestic water in the winter. Yes your right a 3 way valve would resolve this, but I did not want to burn wood all year round. Currently the HWH is on a timer operating 6 hours a day.

EDIT: BTW, I bypass the 20 plate DHWX during the summer months. Re-align for winter operation. We have some iron in our water (well)  and want to extend the life of the DHWX.

Picture of install: http://outdoorwoodfurnaceinfo.com/forum/index.php?action=media;sa=media;in=38;preview

Although none of my pictures in photo album shows this, I insulated all the OBW lines inside the house. Looks professional. 

[muffin]

The documentation for my CB 6048 says to install it prior to the AC coil, but after the fan.  I think you want it post fan so that it is post the filter.  They said it should be before the AC coil so that when it is running you do not freeze your Hx.  I did not think they got that cold, but maybe they do.  It would suck to freeze the water in the Hx and break it!

[RSI]

I had a thermometer on the cold pipe on mine after I last posted and it was running about 45°. I have no idea if that is what they all run but as I said before, the condensation water on them will freeze way before the coil above can freeze.
Just put it where it is easiest to mount it and if you are worried, put a drain on it and drain the water.

[muffin]

The documentation for my CB 6048 says to install it prior to the AC coil, but after the fan.  I think you want it post fan so that it is post the filter.  They said it should be before the AC coil so that when it is running you do not freeze your Hx.  I did not think they got that cold, but maybe they do.  It would suck to freeze the water in the Hx and break it!

Talked to my HVAC guy and he said there is no way the AC unit would freeze it.

[yoderheating]

 I have had one coil freeze and bust but it was on a down draft furnace.

[gmviso]

As I recall, an air conditioning coil when operating at its peak is capable of dropping the temp of the air passing thru it by about 20 degrees. So, you would have to have your thermostat set to 52 degrees or lower for the chilled air after it passes over the A-Coil to be 32 degrees fahrenheit. And I doubt anyone has a compressor so oversized that it could chill the house to 52 degrees anyway. So I don't suspect it's really a problem and will probably install mine after the a-coil because this is a retofit and it will be easier than trying to raise the a-coil. Thanks everyone for your inputs.

[mikenc]

My Ahu has factor installed hot water coil above a-coil, been in for 10 years never had any problem with coil freezing. I would make sure air is filtered before going into coil. Dust particles can stop coil up in no time. I just valve off HWC in summer so I can heat DHW in summer.

[RSI]

I have had one coil freeze and bust but it was on a down draft furnace.

That is really interesting. Was it before or after the A coil and how far from it? Had the A coil iced up?