Heat exchanger install

[fourustircom]

Hi, Folks!

Anyone run into a problem getting a big enough heat exchanger to fit their furnace? We have a Lennox Elite oil furnace with an A/C coil on top. The coil is almost to the top of the plenum. The heat ducting is only 12"x23" where it exits the plenum. That might be a little small. I could probably install at an angle to get a larger exchanger to fir there.

Another suggestion is to install the exchanger in the cold air run. Will a blower motor survive 180 deg. cooling air without overheating?

My B-I-L installed his on top ot the blower, but again, I have even less space there, unless I cut a relief in the bottom of the furnace.

Any thoughts?

 

[2FatGuys]

Please post a sketch or photo to help us understand your situation.

 

[Geez]

I had clearance problems with mine that sounds similar to yours. Not much height to the plenum and an AC coil. My main heat duct exits the back of the plenum at the level of the AC.
I was able to raise the AC about an inch and a half, which gave me enough room to mount the heat exchanger below it, and without affecting air flow out the back duct. There was enough slop in the AC lines to make the move without repiping it. I made brackets to support the exchanger right where the plenum joins the furnace.
And heat exchangers come in many dfferent sizes so you should be able to make it fit. The flat type are about 2 inches thick.

 

[fourustircom]

2" thick heat exchanger?

All the HE's I've have been about 5" thick. 2" might work tf I move the A/C coil up that amount. I guess it wouldn't matter if the A/C coil touched the top of the plenum. There are 2 heat runs that come off the top of the plenum I would have to move if the heat exchanger was positioned in the heat run.

Thanks! That might just work for us if I can find a skinny HE.

 

[zsteinmetz]

I put mine in the return and it works just fine. I had to cut out a section of the return and make a new duct to accomadate the exchanger but all in all i haven went through a fan motor yet. My temp coming out of my registers is about 105 degrees compared to 120 with it on top of the furnace but sometimes you have no choice.

 

[fourustircom]

3.5" exchanger?

I talked to the dealer we'll probably a Woodmaster 4400 from and he thought that a 3.5" heat exchanger might not provide enough heat. Geez, are you happy the the output from the 2" thick job? It looks like I can go with a 19"x19" on top of the furnace.

Thanks!

 

[Geez]

I talked to the dealer we'll probably a Woodmaster 4400 from and he thought that a 3.5" heat exchanger might not provide enough heat. Geez, are you happy the the output from the 2" thick job? It looks like I can go with a 19"x19" on top of the furnace.

Thanks!

All I can tell you is that I've heated my 2000 sq. ft. house entirely with my OWB this year. My propane tank is still sitting at 70% since last year. My heat exchanger is 19" X 20" and I keep the thermostat at 72°. Works very well in my case.

 

[fourustircom]

Heat exchanger

Thanks for the response, Geez. What part of the world are you located? I'm near Flint, MI. How much wood have you used so far? Our house isn't much bigger, so that's good news. Where did you find the 2" exchanger? Got pics of your install? I suppose if it didn't work I could install a second exchanger in the return run. There are 2 extra connections on the back of this Woodmaster 4400 we are considering which I'll probably run along with the main tubing should I need them one day, garage, pool, radiant heater, etc.

Thanks!


Thanks!

 

[Geez]

I'm on the west coast of Wisconsin. The heat exchanger came with my unit so I couldn't tell you the brand but there are all types and sizes available from heating supply companies. I would look at your situation closely and see just how much you can raise the AC coil first. In my case I had much more space than I thought and could've actually had a thicker exchanger. And all it requires is a couple sheet metal 'L' brackets to support it, so you can literally set the AC right on top of the heat exchanger.
I had to set my exchanger so the pipes came out a different side of the plenum than the AC because the intake and exhaust PVC pipes for the furnace interfere with the exchanger plumbing when the exchanger is set that low. Just look at your own situation and plan carefully before you start.
Another little trick that worked well in my case because of the confined conditions and the fact that I didn't disconnect the AC, was to support the AC coil on wires while I worked on the brackets and exchanger below it.
I drilled two 1/8" holes on each side of the plenum and fished pieces of stove wire in, then under the AC and out the other side. By tightening up the wires I lifted and supported the coil until it was ready to set back down. Some sheet metal screws then plugged the holes.

 

[fourustircom]

A/C coil clearance

So, Geez, is your A/C coil right to the top of the plenum? I'm not sure how the air circulates around the thing. Does air flow around the sides and over the top?

I had planned to support the coil some way. It looks HEAVY!

Thanks!

 

[Geez]

So, Geez, is your A/C coil right to the top of the plenum? I'm not sure how the air circulates around the thing. Does air flow around the sides and over the top?

I had planned to support the coil some way. It looks HEAVY!

Thanks!

If your AC coil is the 'A' frame type the air goes up through the center of the bottom and out though the slanted sides. It is much lighter than it looks, and they usually just sit loose on the brackets. Depending upon it's size, your support brackets have to be big enough to block the air flow around the sides, forcing all air to go up through the center of the thing. You will most likely just use the existing brackets and reset them higher. I was pretty surprised that, given the size of the plenum, that the opening up through the AC was so small.
This reminds me, one of the options I was given, before I discovered I could make it all fit, was to go with a FLAT type AC coil. But that would have cost a couple hundred bucks and required recharging the AC. But it IS an option if you can't find room for an exchanger.