How do I wire up a thermostat, heater and a pump?

Old 12-16-09, 05:47 PM
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Location: Colorado Springs
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How do I wire up a thermostat, heater and a pump?

I'm considering fitting a heated floor to my workshop conversion project. I've pulled permits and am within code to heat any way I like. This is considered a 'shop conversion'.

I'd like some help with how to wire thermostats, a heater and a pump to 110V. Only electric is available to the detached shop to heat the water and ideally the heater and pump will be cheap and easy to replace. Controls would ideally be off the shelf items I can wire up with little modification.

Here's a diagram of what I think might accomplish this in a simple way.

T - thermostat
P - pump
H - Heater
Tank is just an insulated water storage tank.
The tube of fluid is to supply under floor heating to a concrete thermal mass, that is to mantain a constant temperature in a room.

Basic logic
- T1 detects a drop in temp and starts the heating process by turning on H.
- The water begins to heat until T2 reaches the target temp and turns on power to P beginning circulation.
- When the cooler return water fills the tank T2 will fall below target temp and stop circulation. This ensures cold water is not circulated.
- The cycle continues until T1 reaches it's target temp switching off the heater. It could optionally turn off the pump as well at this point to prevent the residual heat in the tank being circulated causing the room to overheat.

Another possible solution is to use hot tub parts for the heater and pump. They might be easy to source at little (or no) cost, second hand, but I think the heater would have to run with the pump, which is OK if it will work. It would then only require the T1 to detect the room temp drop and turn on both the heater and pump until the target temp is reached. The concrete thermal mass will help to regulate the temperature. This method would still require a tank, just to allow for expansion. If this is reasonable it should be easier to install and maintain.

Using a large tank has the advantage that a solar heating panel could be retrofitted to supplement the system. Colorado is sunny for most of the winter.

I served a mechanical apprenticeship that involved some electronics and circuit diagrams, but I'm more than a little rusty.

Of course the lower the cost the better. Any input would be appreciated.
Old 12-18-09, 07:02 PM
Join Date: Mar 2000
Location: Arlington, WA
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The system is fairly straight forward, but it would be simplest if the pump were seperate from the water heater -- i.e. a recirculating pump.

You mention 110V power. If that's all you have available it will limit the size of the WH to about 10 to 15 gallons. Is that enough for the system?

A TACO recirc. pump only draws about 23 watts. power comsumption for that is not an issue.
Old 12-18-09, 07:48 PM
Join Date: Mar 2006
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Unless you have insulation under the slab and around the perimeter to isolate the slab from the ground and the side walls you will be throwing away at least half of whatever bit of heat you may get into the slab. Furthermore, radiant slabs are VERY slow to heat and using only a water heater with limited power (120 volts) will most likely be a total waste of time and money with no usable heat at all. Even using a 6,000 watt heater with a 240 volt supply will likely get you zero usable heat but it will make the electric meter spin.

Also, to do it correctly you need a source of "make-up" water and an expansion tank to take care of the expansion when you heat water. Google radiant floor heat for more information

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