Buffer tank thermistor

by **ABCO Heating** » Thu Nov 05, 2009 12:58 pm

I'm installing a buffer tank with my w/w heat pump and need to intall some kind of a thermistor inside the buffer tank to tell my HP when to turn on and off, Or is it better just to use the internal thermistor of the HP for it to cycle. Any suggestions? It's an E-series EW042.

Thanks

by **teetech** » Thu Nov 05, 2009 3:35 pm

You have options> If it is a Waterfurnace buffer tank there is a thermistor already there. If not the unit can be run external with the R & Y signal that leaves even more options. Is this for infloor heating?

by **urthbuoy** » Thu Nov 05, 2009 5:17 pm

We've used both. Nothing wrong with using the existing built-in one on the unit to avoid some extra plumbing.

by **Mark Custis** » Thu Nov 05, 2009 6:05 pm

....control strategies. What do you want it to do when. What is going to read the resistance of the thermistor?

by **ABCO Heating** » Fri Nov 06, 2009 4:53 pm

I spoke with tech support @ waterfurnace & he also said to just use the internal one on the HP. I picked up one of the new Marathon thermal storage tanks & am anxious to hook it up. Also whats the rule of thumb on water storage, my unit is 44kbtu & i have a 50 gallon storage tank, is this to small? I have about 30 gal. in the lines. The waterfurnace tech told me the new rule of thumb is 2 gal/btu. It used to be one i thought now they doubled it.

your thoughts?

Thanks for your input.

by **teetech** » Fri Nov 06, 2009 7:41 pm

I would recommend 80 gallon tank, 30 gallons in the piping is a lot of pipe, assuming this is infloor. I would also want to read the tank temperature instead of the pipe in the unit, unless you want to run the pump continuously. If this is slab heat I would want to have outdoor reset for comfort and efficiency.

There was an earlier post about this and problems with short cycling. Better to do it right the first time than dealing with problems after.

by **urthbuoy** » Sat Nov 07, 2009 2:29 am

The WF unit will call for the circulating pump to run for a <you set this> period of time prior to taking a temp. reading. So, you will get a pretty accurate tank temperature. The one thing you can't set is the number of times it runs in an hour - I believe it comes on 5 or 6 times an hour. If it is a short run from WW unit to buffer tank, I usually just have this set to run for 1min before taking a temp reading.