indirect water heatihg

digger_2

I have been using a 50gal gas standard gas water heater with an input of 40k Btuh with no problems for the last twenty years (only two occupants in home). I am upgrading to a Lochinvar WB-050 and will use it for DWH and a 35k Btuh heating load. My thoughts were to go with a 40gal indirect and set the temp 130*F- 140*F and temper the water with a mixing valve. (for a more consistant temperature)

I have had some suggest that the boiler will be too small. I'm heating 50gal now with a 10yr old AO Smith That probebly has an output of 32k btuh or less. I hate to oversize because the WB-050 modulates down lower than the WB-080.

Am I missing something? 

hot_rod

plenty of power

to heat 40 gallons of water from 50F to 130F



8.33 X 40 (130-50) = 26,656 BTUs.



A 50,000 boiler at 85% efficiency would be 42,500 BTU/hr. output. So even with a perfectly cold (55F) tank that boiler would recover the load in less than 1 hr. Of course the pump and pipe will need to be sized to move that load.





And it"s rare you would pull the entire tank down to 50F as it will be stratified when the cold water enters the bottom.



hr

SpeyFitter

Nice set up...

I think you are pointing yourself in the right direction with that set up. Hell I bet  you could even go with the Lochinvar Squire 30 Gallon Indirect and be fine.

I currently have a 40 gallon bradford white electric hot water tank in my house, and in around a year or so I'll probably have a Lochinvar wb050 and a Squire 30 Gallon. If you look at the Lochinvar tables, the 30 Gallon Squire with the Knight WB050 has more hot water output by around 25%+ than my 40 gallon electric as far as first hour outputs go.

But if you're set on a 40 gallon, go with the Squire. It apparently has a pretty good size indirect heat exchanger to maximize heat output from the boiler.