Thermostat Differential For Circ Pumps Only

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velvetfoot

Minister of Fire
Hearth Supporter
Dec 5, 2005
10,203
Sand Lake, NY
I currently have a .5*F thermostat differential on my baseboard emitter, pellet/oil boiler fed, buffer tank equipped system. So, at a setpoint of 68, the zone circ comes on at 67.5 and shuts off at 68.5. The boilers don't come on and off because of the buffer tank. Running on tank, before a boiler comes on, it gets down to may 130.

I'm thinking of increasing the differential to 1*F, so that a zone circ will come on at 67 and turn off at 69. I'm wondering about the pluses and minuses of doing this.


Pluses:
Pump cycles less. (It is an ECM pump, so maybe not that much of a factor?)
Less getting rid of the cooled water from the pipes

Minuses:
Not as comfortable as .5*F, maybe leading to messing with the thermostat setting

I'm stuck with whatever comes out of the boiler or tank-no mixing on distribution.

On most HVAC systems, is a 1*F differential the norm?

Comments?
 
I think I need to make a correction. With a 1 degree differential at a setpoint of 68, it seems to come on at 67 and go off at 68. Looking at the thermostat spreadsheet, which acquires data every 5 minutes, there might be some inertia, but I don't know if this thermostat takes that into account.