Hot Water Unit Heater- How to wire for Instant Off?

NTL1991

I installed a small Beacon-Morris unit heater in my father's basement workshop/garage a couple years back, and it's worked out great on those chilly days and keeps their field stone basement nice and warm. It was a very simple setup at first, with only a mechanical strap-on Aquastat. After some research, I decided on upgrading the Aquastat to a Ranco Electronic temperature control, which works much, much better and is much more flexible.

The only complaint I'm getting from my father is: "It keeps running after I turn the thermostat off and blows cold air!" I've explained that the fan will turn off automatically when the pipe cools sufficiently and that it's not actually "cold air."

Is there a simple way to give me some "Instant-Off" functionality using the existing White-Rodgers thermostat? Maybe with a small RIBU1C or similar relay to cut the small 120V fan in and out with the 24v thermostat? Would this plain jane stat be powerful enough to trigger the Zone Sentry and a RIBU1C together?



Thanks Guys,
Nick

Zman

I think I would use the end switch on the taco valves to enable the RIB controlling the fan.

NTL1991

I didn't think about using the end switch, that sounds like it would work perfectly. Thank you

Steamhead

Zman said:

I think I would use the end switch on the taco valves to enable the RIB controlling the fan.

This.

unclejohn

It looks like a heat pump stat which means the "G" or fan circuit will energize with a heat call. I would try that before the end switch with a taco valve.

unclejohn

Is the sentry not a 3 wire valve, not familiar with that valve.

rick in Alaska

The problem about enabling the fan as soon as the thermostat calls, is that it will be blowing cold air until the water flowing through it gets hot. Not really a problem if the boiler is up to temp and the line is short. Might want to consider putting a timer on the line to delay the fan start a little, and then delay the shutoff to purge some heat.
Rick

Zman

rick in Alaska said:

The problem about enabling the fan as soon as the thermostat calls, is that it will be blowing cold air until the water flowing through it gets hot. Not really a problem if the boiler is up to temp and the line is short. Might want to consider putting a timer on the line to delay the fan start a little, and then delay the shutoff to purge some heat.
Rick

You could wire the rib in series with the present aquastat or snap disk to assure hot water before fan turns on.

JUGHNE

I would try to change the differential on the Ranco.

Zman

JUGHNE said:

I would try to change the differential on the Ranco.

That would be simple

JUGHNE

Or perhaps this:
The end switch or "G" closes a RIB sending power to the Ranco.
When the Ranco senses hot water flow it turns the fan on.
When tstat drops zone valve end switch or "G" the RIB is off and fan stops now......no cold air.
You can set the Ranco up to deliver the hottest possible air initially. You could be a hero and make points.

EBEBRATT-Ed

From the thermostat (Heat call) power the zone valve open and the Ranco. Go through the Ranco and pull in a rib relay. . Contacts on rib relay start the fan. Fan starts when pipe is hot. When you lose the call for heat the zone valve closes and you drop out the rib and stop the fan.

NTL1991

JUGHNE, This is exactly the kind of setup I was thinking about.

IIRC, the Ranco's memory is non-volatile, so being unpowered for months at a time shouldn't be a problem. There is a slight startup-delay when the Ranco first powers up, but I think it would be negligible.

Thanks for all the help, guys