Constant Circulation Using DPDT Swtich for Freeze Protection

NTL1991

Hello,

It seems like every year I end up having an issue with frozen heating pipes, and I'm wondering if my idea would be feasible to prevent blockages. This is a retrofit Single-zone system, baseboard radiation piped with hePEX (House used to be 1-Pipe Steam). The installer had to be creative (3rd floor - no access from below) and the supply/return pipes run through some cold areas along and through walls, and under kitchen cabinets.

My tenant was on vacation last January and even though he said he set the programmable thermostat to a reasonable temperature, something went wrong. Could've been weak batteries in the T-stat, which failed to close the relay to call for heat. In any event, the apartment got very cold and I had to break out space heaters and heat 100+ feet of piping and baseboard with heat guns until I finally got flow.

Here's my idea:

Installing a switch box near the system circulator, and extending the boiler circuit to it. I'd like to use a DPDT switch, like the Leviton 1282, which has a "Center Off" to isolate two Line feeds during switching. One of the switch positions would be hot all the time (Boiler Circuit from Panel) and the other would be using the existing circulator wiring from the Aquastat. This way, during the coldest time of the winter, I can flip the switch to Continuous Circulation, which I would imagine would prevent freezing, and during milder months, I can flip the switch back to the Aquastat Control.

Any thoughts?

Ironman

That would still require manual operation. You didn't state what type of boiler or controls you have, but I would just use a simple ETC that's sensing ambient temp. Wire the circ to the common terminal, the pump control to the NC terminal and hot to the NO terminal. You may experience slight overheating if you don't have ODR.

NTL1991

Thanks Bob,

I reside in the 3-family so manual operation wouldn't be a problem, but I do like the simplicity of your solution.

I don't think overheating would be an issue at all. Due to the low mass/water content of the cheap "Superior" gas boiler (~85k BTU). The heat loss of the 750 sq ft apartment is about a third of that. (I wish I had known all of this stuff when they were doing the work...)

It's just a typical Honeywell aquastat, L8148 I think. Circulator is a 3-speed Taco 00R.

Would you have any recommendations on an ETC to use?

Thanks,
Nick

Zman

How do you feel about glycol?

Ironman

Johnson A419 is the one I've had no issues with. No problems with the Emerson one either, but it's more complex.

Glycol works even during power failures, but it will reduce the available btus somewhat. It also should be checked for its PH level and strength every year.

NTL1991

Thank you Zman and Bob. Glycol seems like it would work well; I have to look into that option.

The A419 looks perfect. Once below a set ambient temperature, the circulator would run continuously, and return control to the boiler controls once it was warmer. That would give me near perfect efficiency as far as excess power usage vs. risk of freezing goes, without relying on my being there to operate it.

Thanks again,
Nick

HDE

Nick it wasn't mentioned, but the sensor for the A419 should be outside, right? Indoor sensing may not catch the temp drop inside.
BTW, I have used these for pool freeze protection, it makes an excellent digital domestic control and so on.

NTL1991

Thanks HDE, I figured the sensor lead would need to be routed outside. With 3 boilers, 3 hot water heaters and 3 pairs of washers & dryers, the basement can be quite toasty in the winter. It definitely wouldn't be cold enough to trigger the switch.

Thanks for the heads up,
Nick