# OWB installing heat exchanger location



## trt3 (Oct 16, 2009)

I am in the middle of hooking up an outdoor wood boiler and have a question. I am installing the heat exchanger into my ducting and there are only two options. One is to install it into the return line but I think I will lose some heat that way plus I will have to make a place to put a new air filter above the exchanger (the present air filter is on the bottom of the furnace right at the blower). The other option ,which is the easiest, is to mount it under the A coil but this will put it right above the heat outlet from the oil furnace. It will be about 5 or 6 inches from it. Is this to close. The oil furnace I have is tall and has the return line and feed line both on top of the furnace so I don't have many options. I can make it work either way but the feed line with the A coil is the easiest. I can send a picture if it helps.


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## Steveguy (Oct 16, 2009)

Between the furnace and the A-coil in the discharge plenum is the preferred location for your HX . In my application there wasn't room there so I had to put it in the plenum above the AC A-coil. Some people are concerned about freezing th HX in the summer with it above the AC , but I don't think it would happen. It hasn't for me anyway. So, it sounds like you are on the right track.


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## nparch726 (Oct 16, 2009)

I put mine just a couple inches above the A/C coil. I think I heard on here about the HX freezing when the A/C is on in the summer, but I have a hard time buying that one. I just fired up my new OWB last week and so far everything is working great with my setup. Good luck!


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## trt3 (Oct 16, 2009)

There is no room on top of the a coil so it has to go under it. There is about 9 inches between the furnace and a coil in the plenum. My concern was how close is to close to the oil furnace. I guess I am concerned about the heat that comes from the fire box of the oil furnace.


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## Geez (Oct 17, 2009)

I had the same situation and installed the HX right above the furnace. The A coil vitually sits right on top of it. No problems with either the heat or the AC operation.


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## applefarmer (Oct 17, 2009)

I had the same problem with my setup in my low headroom basement. My hx was the same diminsion as the hot air discharge on the oil burner. I trimmed the lip off the sheetmetal on the furnace and mounted the hx directly to it. Then remade a hot air plenum to mount to the top of the hx. Worked great no problems!


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## mtfallsmikey (Oct 19, 2009)

Steveguy said:


> Between the furnace and the A-coil in the discharge plenum is the preferred location for your HX . In my application there wasn't room there so I had to put it in the plenum above the AC A-coil. Some people are concerned about freezing th HX in the summer with it above the AC , but I don't think it would happen. It hasn't for me anyway. So, it sounds like you are on the right track.



If the HX gets that cold, there will be a lot more going wrong first...like a frozen evap. coil. Most of the time, discharge temp. from an A.C. evap will be in the low 50's


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## beagledog (Oct 19, 2009)

Mine is about 12 inches from the oil burner chamber. No problems.


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## mikenc (Oct 19, 2009)

My hot water coil came factory installed above A coil in air handler. Never no problems with freezing. I think it is best to install HWC on discharge side of fan, supply side of ductwork if possible.


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## upsnake (Dec 19, 2010)

Ok i know this is an old thread, but I am in the same boat. I am getting close to having the install done, and when i started looking at the furnace, the AC coil sits right on top of the furnace. 

I think i can move it up the 6 inches to get the HX in there but it would be a lot less work to put it on top of the AC coil. 

I don't use my AC that much, i think last summer I might have used it 5 times. I don't want to mess up my HX though. Haha I am not sure if any of the people that said they did the install this way are still actively reading the boards but if they are or if anybody else did the install this way how is it working for you?

Thanks
Jay


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## loadthestove (Dec 19, 2010)

I installed on my cold air return side.my heat exchager is fastened directly on furnace inside return air duct work.


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## boyland (Dec 19, 2010)

I have 4 different furnaces in my house, I have it installed on the returns on 2 downflow units, installed above the a coil on one, have below the a coil on another. I measure the duct temps, they run about the same. I cannot see any difference where the coil goes.


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## 1harlowr (Dec 20, 2010)

The outlet temps on my heating vents are higher with the OWB than the propane furnace. I'd think that would be the same case with your oil furnace. That tells me the heat from the propane furance is lower than the temps coming off my OWB HX. I could be wrong, if so, someone correct me.


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## mtfallsmikey (Dec 20, 2010)

1harlowr said:


> The outlet temps on my heating vents are higher with the OWB than the propane furnace. I'd think that would be the same case with your oil furnace. That tells me the heat from the propane furance is lower than the temps coming off my OWB HX. I could be wrong, if so, someone correct me.




Not sure what outlet air temps. these new furnaces are producing, industry standard used to be 190 deg. After return air drop, and fan speed corrections, you should have, for example 130-140 deg. air temp. from a coil supplied with 180-190 deg. water. Mine averages 130 or so.


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## coyotencuttin (Dec 20, 2010)

If you put the hx in the return make sure you have a high quality air filter installed before the air enters the hx.air flow is the biggest reason why a/c coils are installed after the blower. You move more air after the fan than before it. Generally return duct work is sized larger than the supply ductwork and if you need X cfm for the proper btu from the hx you may only get 1/3 or 1/2 the btu in the location. Something to think about. Good luck, Harold


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## Penguins87 (Dec 20, 2010)

Upsnake, I had the same situation as you. I installed my HX above AC coil in the plenum. Now three years later I have had no problems. But one thing I did was put a shut off valve on the feed side followed by a boiler drain right before the HX. Then another shut of on the return side. Isolating the HX. When I shut my OWB off for the summer. I close both valves and open boiler drain which would allow for expansion if there is freezing. In the fall, close boiler drain and open the two valves. Don't think it's was necessary though.


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## i'mstihlaguy (Dec 21, 2010)

Penguins87 said:


> Upsnake, I had the same situation as you. I installed my HX above AC coil in the plenum. Now three years later I have had no problems. But one thing I did was put a shut off valve on the feed side followed by a boiler drain right before the HX. Then another shut of on the return side. Isolating the HX. When I shut my OWB off for the summer. I close both valves and open boiler drain which would allow for expansion if there is freezing. In the fall, close boiler drain and open the two valves. Don't think it's was necessary though.



I kinda did the same thing. More for maintenance and so I could bypass the HX. I have a single loop so this lets me bypass the HX and still supply the side arm on my hot water heater. I have unions at the HX for removal if necessary but I haven't had any issues leaving it installed. The air handler was oversized a little to ensure proper air flow.


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## woodcuter ms361 (Dec 21, 2010)

Just started building me a owb,all my duck work is overhead in my home,has anyone put hx overhead?where is a good place to buy heat exchanger?Thanks


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## mhyme71 (Dec 21, 2010)

This is how i did mine. I added a illustration from central boilers website. They know a little something about these owbs


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## upsnake (Dec 22, 2010)

mhyme71: Do you have AC in your house? If so I am assuming that your evaporator coil sat far enough above the furnace in the plenum that you could put your HX in.

That was my plan (CB's recommendation) until I opened up the plenum to see the AC coil sitting right on top of the furnace.  haha 


i'mstihlaguy & Penguins87: I like that idea. I am planning on going that route, as it will save a lot of time and money redoing the furnace plenum, and eliminate the possibility of damaging the HX during the summer.

Thanks for all of the ideas and suggestions.

Jay


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## Penguins87 (Dec 22, 2010)

Glad to assist! Let us know how you make out. Also you might already be aware of this but I'll tell ya anyway. When looking at your water to air HX's inlet/outlet they are offset, the low one is the inlet and high is the outlet. Flow is better that way and air purges through better also. Secondly, when installing my system most diagrams shown the incoming hot water flow going to the water to water HX (domestic hot water) first, then to furnace. I feel/felt that I want a warm house first and the heat that is left I'll heat my hot water. So my flow goes to the furnace HX and then to the hot water heater HX. Works great!!! I still even had to install a mixing valve on my domestic hot water cause it was to hot. OWB settings are 160 on 168 off. Just a thought. To each is own.


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## upsnake (Dec 22, 2010)

Hmmm interesting thought on the furnace first. 

A little bit off top from the HX, but still in the install process. One of the parts the dealer gave me was a valve that goes in right after the insulated pex comes into the house. Its purpose is to measure the temp of the water coming from the owb. If the temp is above 180 it allows all of the water to pass through to the hot water heater and the hx.

If it was between 150 and 180, it allows partial flow, and below 150 it closes the flow to the hx and hwh, and sends it all back to the OWB. The reasoning behind it they said was to help keep the temp up in the owb to help reduce condensation in the owb. (or something like that, I am still reading it over).

The thing that doesn't make sense to me about that is if the OWB goes out then propane furnace can be a backup heating the water through the hx and sending it back to the OWB. 

As anybody installed this? If so does it still allow you to use your gas furnace as a backup to the owb (for water heating purposes).


On a happy side note, the OWB comes today, now I just have to get the inside plumbing stuff done.  It is getting close.


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## mtfallsmikey (Dec 22, 2010)

upsnake said:


> Hmmm interesting thought on the furnace first.
> 
> A little bit off top from the HX, but still in the install process. One of the parts the dealer gave me was a valve that goes in right after the insulated pex comes into the house. Its purpose is to measure the temp of the water coming from the owb. If the temp is above 180 it allows all of the water to pass through to the hot water heater and the hx.
> 
> ...



I would like to see exactly what this valve is....

Also, doing your piping by the CB diagram is ok, I guess, but doing it in the primary-secondary method is far superior, more efficient, than feeding your HX's in series.


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## upsnake (Dec 22, 2010)

I will upload the PDF of the bypass instructions when i get home today. The dealer said it had to be installed else it would void the warranty (which seemed kind of harsh but...)


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## mhyme71 (Dec 22, 2010)

*upsnake*

yeah you might have to do some sheet metal work. but my a coil is sitting right on top of my heat ex. there might be 4 to 6 inches of clearance between the two.


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## rick2752 (Dec 23, 2010)

I wouldnt install that valve. I like the idea that if something were to happen and the fire went out and my furnace kicked on, that it would partially heat the boiler water to keep it from freezing.


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## upsnake (Dec 23, 2010)

I didn't get a chance to scan the instructions sheet. Was busy getting the boiler in place. Haha
I did look at the instruction and ask the dealer and they both said that it will not prevent the gas furnace from heating the water if some was to happen to the OWB. I don't see how but...


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## upsnake (Dec 23, 2010)

Has anybody ran into their water heater having a high temp limit switch issue. The instruction manual said if your water heater has that you may have issues trying to use a side arm hx. I checked the gas valve on mine and it appears that it does. 


I have tried searching online for info on it but failing pretty big. Haha Just thought i would toss that out here. 

Thanks
Jay


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## i'mstihlaguy (Dec 29, 2010)

Jay,
My water heater is electric and I have a side arm. The high temp limit switch tripped once but I didn't notice it of course until I shut down my OWB for the summer and the supply of hot water went south. Pulled the access cover off and pushed the reset button and I was back in business. I believe the main function is to ensure your water at the faucet doesn't get too hot. A mixing valve can be installed to regulate the water temp. being supplied to your faucet. Disclaimer: I do not know if it has anything to do with protecting the equipment.

Bill


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