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[gtownky]

Does anyone see if there would be any issues with coming off the return side of my 100 plate water to water heat exchanger that returns to the OWB and installing a plate heat exchanger to a hot water heater. I have 2 hot water heaters and maybe was even thinking of running to both of them before returning to the burner. Whats your thoughts. Also how many plate exchanger on the DHW heaters. One hot water heater is for the kitchen and washer and the other is for 2 bath rooms. The previous owner didnt like waiting for hot water at the kitchen sink.Also do I hook these up at the intake of DHW heater or after? Thanks for the help. Also im running a B&G pl-36 pump that runs 24/7

[slimjim]

What you are looking to do is fine as long as you don't restrict the flow of the main loop, oversize the heat exchanger and install ball valves and purge ports for future cleaning.

[gtownky]

How many plate on the DHW exchanger?

[LittleJohn]

How many plate on the DHW exchanger?

From previous trolling of this forum, I have heard as small as a 20 plate will work for dhw, but you will want to pay attention to the head pressure across HX.  By running HX's in series you run the risk of increased head pressure issues.  Just becareful with using OWB to heat DHW, OWB operate up to 180F and technically any hot water over 120 can scald, so you will probably require mixing valve on potabel side of hot water heater.

[Sloppy_Snood]

Just becareful with using OWB to heat DHW, OWB operate up to 180F and technically any hot water over 120 can scald, so you will probably require mixing valve on potabel side of hot water heater.

Would a mixing valve be required for a plate exchanger or side arm in any system?  What situation would not require a mixing valve? 

[racnruss]

Well, mixing valves are a good thing, especially for kids or company that may not be aware of HOT water.

However, without a mixing valve, probably the safest way I can think of would be to run your domestic water through the plate exchanger on its way before the water heater.   That way you are preheating the water going into the water heater and you have a 40 gallon or so buffer in the water heater.

[CountryBoyJohn]

You won't hit 180 with a 20-plate exchanger.  The highest I've recorded mine was around 135.  I don't have a mixing valve in right now, but I plan on one in the future.  To get 180 degree temps, you would have to use a side arm and it would have to circulate for quite a while.  The exchanging process is too short in a 20-plate to get the water temp that high. 

Mr. Snood, plate exchangers work best in normal to high-use situations where side arms (without a dedicated circulation pump) are for typically infrequent low use situations. 

[Sloppy_Snood]

Thanks for the information CBJohn.  What is the "standard size" (number of plates ) for a water heater plate heat exchanger?  20?   

Just trying to ascertain what is a "typical" plate exchanger for hot water and when a larger plate exchanger might be needed or desired. 

[CountryBoyJohn]

20 is the norm for domestic water.  A few guys have 10, but others argue it restricts flow too much.  The large plate exchangers, 40-60 plate, are for you pressurized oil boiler systems that the guys use up north.

[LittleJohn]

Agree with COUNTRYBOY, only real advanage to more plates other than lighting pocket book, is generally large inlets and reduction in head pressure across HX.  Also, recovery time for water heater should be quicker cause you will either be moving more GPM, and thus more BTUs