Thread: Hx

I am putting in an OWB and was wondering about what size of tubes I should get 1" or 3/4" If it even matters. I am putting in 1" underground coming into the house and then it will go to 1" copper to a distribution center where 1 line will go to DHW and the other to the HX. I will also have a couple of extra lines for future use. Also where is the best place to get a good quality HX? Thanks

Good morning!...Did you do a search yet?...we have pounded these kind of subjects into the dirt....I used Heil coils myself, no problems. See disclaimer below:

The info. I got through central boiler recommends running the heat exchangers in series, First the water heater heat exchanger, and the forced air HX next, then any infloor heat systems. You do need a mixing valve on your hot water plumbing to make sure you can't get scalded because the water heater temp gets up to the boiler temp. You also use a mixing valve on infloor heat to blend the temp down to about 120. If you are going to hook everything up in series, it is a good idea to get a heat exchanger with 1" lines so you don't restrict flow through the system. There was also another thread on here talking about a guy that had a HX that wasn't quite big enough, and in cold weather his forced air ran almost continuously. You should get an HX that is rated higher than your forced air furnace output to make sure you get enough heat out of it. I think HX coils are rated at very high temps (195-200?) so if you are running 170 degree water to them they put out less heat. I got heat exchangers and parts through a guy with a flea-bay store called freeheat4u2 . He carrys alot of stuff and has pretty good prices on HX coils. I bought insulated pex and a bunch of stuff so I actually drove there, (Eastern Wi.) but of course he ships anywhere.

I don't run mine in series..I use primary/secondary piping, which runs a loop (primary) from the boiler and back, circ. runs continuously. The loop(s) going to the HX's tee off the primary,run thru a separate circ., which runs on demand, then back to the primary loop...smaller circs. can be used, temp. loss thru HX's is kept at a minimum...better detail about it on heatinghelp.com.

That works good, the only thing is you need three pumps instead of one. An advantage is you can also put a temp. control on the pump that circulates through the heat exchanger on your domestic water heater and control hot water temp that way. If you don't have circulator pumps on each branch of the system, the water from the boiler will take the easiest path back to the boiler and the other part won't heat well.I do have primary/ secondary loop with circulator pump in my shop and it works well. As far as heat loss through the heat exchangers, if the heat exchangers are located in a heated space anyway, all they are doing is providing more heat. The only time this is a problem is when the weather is very mild, the house may get warmer than desired. I haven't had a problem with this so far.

Originally Posted by Steveguy

As far as heat loss through the heat exchangers, if the heat exchangers are located in a heated space anyway, all they are doing is providing more heat. The only time this is a problem is when the weather is very mild, the house may get warmer than desired. I haven't had a problem with this so far.

I'm in this situation right now....I was in a hurry to get my OWB hooked up this winter and hooked my hot water tank exhanger and forced air coil in series then back to the boiler, no secondary pumps....during the winter I liked it for the excess bit of heat the exchanger gave off...always hated my furnace fan running (bad location in house, noise etc) and it ran noticably less this winter even with such a cold winter, I liked it...now that's it's warmer my house is getting to warmer than I'd like...another drawback is with the heat exchanger "oozing" heat all winter..again it was fine during the winter while it was cold but as it started to warm up I noticed the ends of the house getting cold but the thermostat said the house was warm enough...obviously it was too close to the heat coming out of the furnace...would I change to a dedicated circulator? Maybe, not sure I'm up for digging into it right now and spending the money on another pump etc but maybe some day, certainly not a must have item but can make things more comfortable.

If my propane furnace is 80000 btu should I get a hx larger than that say 100,000 btu?

I would put as big a HX as will fit the plenum size, it will probably be in the 100-150 range, you should be fine. I agree with the previous poster about over heating in warmer weather with the continuous circulation through the HX, you will have to decide if it is worth another pump etc. Now would be the time to do it that way if you want. I have ball valves plumbed into mine so I can manually bypass it if I want. They were originally installed so I can isolate the coil and drain it in summer to avoid freezing it as it is above the air conditioning coil in my system. I heard this was possible but i haven't drained it and it hasn't bothered. With all the airflow across the coils I doubt it would, but I figured the valves may be handy anyway.

Originally Posted by Steveguy

I would put as big a HX as will fit the plenum size.

My propane furnace is rated 100k so that is the size of hx I bought for the boiler. That was a mistake and I am going to get the 125k hx this spring or summer. I would like to go even bigger, but the plenum is only large enough for the next size up.

With the 100k hx my furnace fan runs A LOT!