4 wire for 2 stage

mtbe

My dad had a 2 stage furnace installed in 2020. During an annual lmaintenance today, they found that the thermostat isn't 2 stage AND there is only 4 wires.

Is it possible to use the 4 wires for a 2 stage OR is there a wireless option to install a 'receiver' in the furnace to receive signals from the thermostat?

Pulling new wires will be very difficult.

mattmia2

Honeywell and Tekmar I think both make thermostats that can have a remote control and sensor in the living space and all the contact closures for the equipment at the equipment with the 2 connected with 2 wires. Many furnaces can be set to call the second stage on a timer if the heat call isn't satisfied after a certain period of time although a thermostat could make that decision better but I'm not sure there are many thermostats that do much more than time. Ideally it would be based more on differential between current temp and setpoint.

EdTheHeaterMan

Your 2 stage furnace has the capability to operate on a single stage thermostat. there are dip switches on the control board where the thermostat gets connected. The logic goes like this.

• When properly set up you will get a call for heat from W on the thermostat to W1 on the furnace control.
• If stage 1 is all you need then the thermostat should be satisfied within 30 minutes (that time may be adjustabe)
• If the call for heat is longer than 30 minutes then stage 2 on the furnace will engage after 30 minutes
• Then stage 2 will satisfy the thermostat and the call for heat is over.

The disadvantage to this is that when the call for heat is over, the lower stage will not continue to operate as it would with a 2 stage thermostat. You are getting 1/2 the benefit of that furnace, so you are saving. The other half of the savings will not actually save you that much more, so the installer will often set it up with the one stage thermostat.

If your gas usage for heating in one month is about $200.00 a month, upgrading to a 2 stage thermostat might save you another 3 dollars a month. Weigh that savings against the cost of all you need to do to get a 2 stage thermostat to work.

mtbe

Thank you very much. Just pulled the manual…thankfully my dad keeps them, and found the dip switches for the furnace to go into 2nd stage after a certain amount of time.

Those SOB contractors either didn't know about these things or they wanted to sell something we didn't need.

HVACNUT

It might be more than you're looking for, but you can get 2 stage at the thermostat with a Honeywell RedLink setup, and a Honeywell Equipment Interface Module. Only 2 wires needed at the thermostat. 24 vac constant.

Kaos

It is very common for a typical furnace to be 2x oversized. I had one of these where the original installer only connected the thermostat to the high stage. Moved it over to the low stage and it still heated without issues. In this case there was really no point in wiring the 2nd stage.

A furnace running near continuously in the winter is fine as long as it is maintain temperature. The longer runtimes are also always better for winter comfort.

ratio

There are a number of add-a-wire type devices available, e.g.:

https://venstar.com/thermostats/accessories/add-a-wire/

ISTR one that communicated all (G, W1, W2, Y1, Y2, O/B) over a singe pair, but I haven't been able to find it in the last 20 seconds of googling.

In addition to the Honeywell TH8xxR thermostat with EIM (completely wireless—the 24VAC power for the stat can come from a 2nd source), there is a Carrier Edge thermostat that can separate from & then wire to the base with a single pair (18/2) as well. (The WiFi version, TH8321WF, is NOT compatible with RedLINK wireless accessories. You can get internet access to the RedLINK version with a RedLINK Ethernet gateway)

Protip: With the Honeywells, you can use the (slightly) cheaper single stage stat to control your multistage unit because the EIM has a full compliment of contacts.

mattmia2

https://forum.heatinghelp.com/discussion/comment/1817570#Comment_1817570

you will also get more even heat with the 2 stage stat