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[lindnova]

I am considering replacing my sidearm tube heat exchanger with a flat plate.  The tube never thermosiphoned and I have it in series  before the heater tank now, but I think it is only heating about half of my hot water.  It is about a foot taller than my short power vented heater and that is why it wouldn't thermosiphon.

Anyway, the reason I didn't go with a flat plate in the first place was it was a new house build and the inspector wouldn't allow an exchanger that could allow boiler water to mix with domestic.  I wonder how much of a concern that would be for me as the domestic water is at 50-70 PSI and the boiler water is much less.  Probably less than 15 ft of head pressure from top of furnace, so maybe 20 psi?  If it did leak I would have an overflowing furnace before treated water would get in my shower. 

I found double wall exchangers on pex supply for about 10x20 10 plate $600.00 or 5x13 20 plate $721.00.  I can find good standard 20 plate exchangers online for under $200.

Should I have any concern about installing a regular one inline before the heater tank?  I have been wanting to do this for a while.  With propane prices and my tank at 30% I am looking at not having to buy propane until the middle of the summer when prices hopefully will come down. 

[wissel12]

If you want a standard 20 Plate.  Outdoor Furnace Supply has them for $149.00.  Badger Insulated pipe has them for $129.60.
Badger has shipping and Outdoor has free shipping over $99.00.   Outdoor is on Amzon.

[bajonesy77]

Buy a quality plate hx 5x12 1"mpt and forget that double wall stuff unless you have a lot of money you just want to spend or have to meet "code". Quality ones are 316 stainless and are copper brazed and what most on here have I'm sure.

[lindnova]

Thanks for the replies.  That is what I thought.  I think I will get one.  Haven't cut and soldered copper for a while.  The one on Outdoor Furnace Supply is UL Rated, not sure on Badger. 

I hate hearing the water heater coming on when I know I could heat without it.  I would think the investment would pay off in less than a year.

[ITO]

 I have had a single wall flat plate hooked to a loop with my indoor pressurized boiler on one side and my OWB on the other for 10 years with no problems. Put a couple hose bibs and valves on the OWB side for back flushing the HX as well as filling the OWB, some say unions to remove and flush but I don't see why a person would want to remove if you can flush it in place. I have a bypass piped in on the pressurized side also because I run my indoor boiler in the summer for DHW and also in case of OWB problems.

[LittleJohn]

I live in MN, and technically you are supposed to run double walls between closed loop and potable.

That being said most closed loop systems I have see are 10-15 psi (pressure relief valve at 30-35psi), open loop systems are even less accept on outfeed of pump potentially; most potable water is min of 45 psi, so if you did have an internal leak would the water leak out of Potable and in OWB side releasing the pressure relief valve or pushing water out the top of your boiler???   

[ITO]

I guess I should clarify, my HX is between my boiler systems not potable, my loops feed a water tank not through a potable water heater.

[lindnova]

Little John,

I live in Minnesota also.  I have high water pressure - 50-75psi, so I would have water running out the top of the boiler from a leak.  I guess I am just looking for reassurance that my though process is correct.

[Lancealott]

Just put a curculator pump on the sidearm.  You said you can hear it run so is it gas or oil.  If so you can probably use the control for the tank to run it.  Also this setup runs more efficient if you t your cold inlet at the bottom ant then run it into the tank at the cold inlet not at the blow off.  You will be able to control your temp and won't need a tempering valve.