Water to air heat exchanger in return plenum. OK with low temp?

[chadhumm]

I was planning on installing a water to air heat exchange, the return plenum would be a very easy install. The supply side very difficult if possible at all just based on the space between the furnace coil and basement ceiling.

From what ive been reading it sounds like the main reason it is not recommended in the return plenum is because of the higher temperatures entering the furnace fan. Im using water from a corn stove and I can control the temperature and was going to use a lot cooler temperature than what you get with an outdoor wood boiler. Would 90 to 120 degrees be acceptable on the return side entering the furnace fan. I have an azule furnace fan motor that is programmable so i can match the fan speed to the hot water coming in, so its for the most part a constant on, instead of intermittent . It will be a very low fan speed 12% of the full capacity. It will be hooked to an aquastat so when there isnt hot water the fan shuts off..Thanks for any advice.

 

[hondaracer2oo4]

I think that you would be fine as far as the heat goes entering the fan. I can't imagine that would significantly reduce to the life but you should check the label on the motor for a max ambient temp rating. I would say that your system "may" work to your satisfaction. You will definitely need to move the air constantly and at a low CFm. Any blowing air temp below your body temp feels like a cold breeze.

 

[warno]

This is just coming from my garage system which is 2 small water to air HX in the end of the supply ducts at each end of my garage. My fan blows on low when it runs. My ceiling has no insulation and there is r13 in the walls. My system simply would not work at temps below 145°F. It would feel like blowing cool air and the garage would not warm up at all. I would be worried about running temps that low in "hopes" that it worked. I would do everything I could to stuff that coil in the supply side and run it hot.

 

[DoubleB]

A double whammy--there wouldn't be much heat in your air, and you're talking not much airflow anyways to avoid feeling the cool breeze.

For those reasons there might be such little heat transfer possible that you wouldn't be worse off putting a tiny HX in your supply side in what little space you have.

Not to mention other things like unfiltered air going through a return side HX, which could cause further problems with clogging your HX.

I'm not smart enough to know all the potential problems, but that's why I would try to avoid it.

If you post pictures that likely might generate some more ideas or options for you.

 

[Tennman]

Based on what I see in my filters, I'd never do it. Not sure how significant the heat loss would be because you'll be warming the fan blades, but there will be some energy loss. Trying to imagine the negative having the flow restriction on the suction side of the blower. Usually when you never see it recommended there's good reasons out there. Sorry to complicate your life. You may go onto an HVAC site and ask some questions. It's pretty quiet here this time of year. Cheers.