Millivolt programable heat only thermostat?

[Rothrock42]

My greenhouse has a gas furnace and thermostat that works on a millivolt system, that is they don't require mains electricity and will continue to function even if the power goes out.

But since the thermostat is millivolt, it doesn't have the ability to run a schedule of "a bit warmer during the day and a bit cooler at night" It only has one set point.

I was thinking that there might be a battery powered millivolt thermostat out there where the battery runs the clock for different day/night time settings. But I'm having a hard time finding that and most of them seem to be non-programmable.

So here is what I'm looking for and wondering if anybody has experience and can recommend a reliable thermostat.

• Only heat. I don't need extra inputs for fan or AC; that just complicates things.

• Doesn't require connection to mains electricity, i.e., millivolt compatible

• Able to set a schedule like 10:00a to 4:00p minimum 70 and 4:00p to 10:00a minimum 60.

• At least somewhat moisture resistant since it will be in the greenhouse.

Thanks for any advice or suggestions.

[Bayard]

Hi, you can buy a programmable millivolt thermostat at at Lowe’s or Home Depot. It isn’t obvious, but one that runs on batteries from Honeywell should do the job.

[Ray]

Personally, I recommend setting a minimum acceptable temperature and letting the sunlight dictate the daytime temperature.

Raising the temperature speeds up the plants’ metabolisms. Doing so while the light level isn’t commensurate can lead to less-sturdy, leggy growth.

[Rothrock42]

Bayard -- thanks for the suggestion. I was looking at their site's, but they put too much junk into their on-line versions. If I go to the store it will probably make more sense.

Ray -- thanks for that perspective. I hadn't thought about it like that. Here in PNW we don't get much sun for several months and I mostly do just want to go with the solar cycle. I was planning on leaving the night-time in the 57-60 range and setting a daytime around 65. Just to give it a little difference on those grey days. (I see I put 70 up above, but that was just an example.) But that might be too much added complication for no benefit. I don't really have any complaints from the plants as it is.

[Ray]

I hadn’t thought about the ilight levels.

Have you considered supplementing that over the winter?

[Rothrock42]

Nope not going to be supplementing the light levels. None of the other growers around here do that -- occasionally I see one bench for seedlings or some other specific purpose.

But a couple other growers at the society said they were doing the scheduled heating, which is where I got the idea.

I've only had them out there since September, but they are growing--slowly--starting roots and sending out bloom spikes. Overall (at least so far) the plants haven't complained.

[Tony Meola]

Just a moment...

What about one of these?

[Rothrock42]

@Tony Meola -- Thanks for the suggestion. That is along the lines of what I'm looking for, but that specific one is a bit too complicated. It has controls for Heat, Cool, and a Fan. That means there are going to be a lot of terminals inside and I'm not sure I would be able to hook it up correctly.

Oddly when I search that site for Heat only I'm not sure that any of them would work on millivolt/battery alone and the least expensive one is more than $50. Which seems excessive.

Our society met last night and I talked to the guy who started me on this quest. The ones he is using are inexpensive, but do have to be plugged in. He also said they tend to die fairly frequently because they aren't specifically designed for the challenging greenhouse environment.

Given all the ideas presented so far, I'm thinking that unless the plants start complaining I'll just leave it as is -- at least for this cold season. Next year maybe I'll revisit the idea. Thank you everyone.