TL:DR/Bottom Line Up Front
I want a programmable thermostat that can read outside temperate and cycle heat. Sorry for the wall of text.
The Deets:
I live in CT, our winters are cold, I live in an old house and have ~6' of baseboard heating copper pipe running through unheated attic space.
With oil being expensive when we moved in, I installed a wood pellet stove to heat and things were warm. Generally we burn 1k gallons oil/year to keep the house at a modest 65F (yes I've insulated the attic already, windows are thermalpane, but it's a big house and I suspect the wall insulation is poor at best). Alternatively, I can burn ~4 tons of wood pellets with the oil providing hot water to the tune of ~150-200 gal/yr (hopefully less since we just replaced the furnace and added an indirect heater).
Our pellet stove does a pretty good job at heating the house, but the problem is when it gets really cold and we risk freezing a pipe in 2 unheated attic spaces where the copper baseboard heating pipe runs. We had a mild disaster the last winter we used the pellet stove exclusively for heating the house when the outside temperature neared 0F and a baseboard heating pipe froze. Luckily only about a quart of water leaked out before we caught it so damage was minimal. After that, I obsessively & anxiously watched the outside temperature so I'd turn the heat on when it got cold out, independent of whether we needed the baseboard heat on to heat the house.
Then oil got cheap, I got tired of dealing with wood pellets and we had a couple kids - so we burned oil.
Welp, oil's expensive again (no politics please...), so it's time to clean out and fire up the pellet stove again. I can't really move the pipes into the heated space, and can't even really move one into the wall or insulated space without doing a ton of work. I am going to wrap the pipes in foam insulation though. In addition, I want a new thermostat for the oil heat that functions as a normal thermostat (so it's a backup if the pellet stove fails to turn on) but also can cycle the heat on for 5 minutes every hour when outside temperature drops below a threshold - let's say 15F.
I doubt there's an off the shelf solution out there, but figured I'd poll the braintrust first. It may be a good Arduino or RaspberryPI project. What say ye?
I'm guessing the thermostat is just providing a simple normally open dry contact to turn on the oil furnace so it would be very easy to add extra controllers with there contacts in parallel to do what you want. I'd continue using your current thermostat to control for heat in the house (or replace it with a better programmable unit if you want to upgrade) and then a separate arduino (or something similar) just setup to monitor outside temps and do the cycling to keep things from freezing. With an arduino you could even dial in that timing based on outside temps to have the cycle time adjust as things get colder out.
If you can reach the pipes to put foam insulation on them, could you wrap the pipes in electric heat tape? It has its own thermostat and turns on at ~40 degrees. Eg https://www.amazon.com/VEVOR-Heating-Thermostat-Protects-Freezing/dp/B0BF57RYXY
Disclaimer: I researched this a bit a few years ago when we had pipes in an outer wall freeze, but I never did it and we don't have that house any more, so I have no actual experience with the heat tape.
In reply to alphahotel :
Responding to also propose a dead simple solution of heat tape. If you are strategic with the sensor location the heat tape will shut itself off when the pipe is warm from flowing hot water.
+1 for heat tape being the simple solution.
Another question though: Is the water in the pipes pumped in some way, or moved via natural convection? could extend/run a section of pipe near/around/through/whatever the pellet stove so when that is on it is also heating the water volume in that system?
Look into a programmable aquastat. I just installed one, worries include water condensation leading to boiler corrosion/early death and general Murphy's fopaux of swapping a simple working part with a complex part. It is saving me fuel already however.
I bought a hydrostat 3250, there are a few different "smart" aquastats and outdoor reset aquastats by different manufacture.
I dreamt of "cycling" the flow to utilize latent heat, they do this on first call for heat and call it "purge" not exactly what you are asking, but close https://hydrolevel.com/fuel-smart-hydrostat-3200-plus3250-plus/
any internet connected thermostat (like the nest) should be able to work with "If this than that" IFTTT which should be able to pull external air temps from an internet source.
https://ifttt.com/p/nest
https://ifttt.com/explore/weather-automations
something like "if the temperature outside goes below xx, turn on heat on NEST thermostat to YY" where YY is 2-3 degrees warmer than the current temp in the house (this way you ensure that the NEST actually turns on)
i actually found something that might even be out of the box:
https://ifttt.com/tado_heating
https://ifttt.com/applets/jDHVCti7-if-the-temperature-outside-drops-below-___-c-then-set-your-tado-to-___-c
and if you want to keep it to on/off: https://www.tado.com/all-en/wireless-smart-thermostat
+3 or so on the heat tape kit. Cheap to buy, cheap to run, and easy to install.
The only other thing I could suggest is two thermostats. One outside or in your space that has the ability to override the household thermostat. Basically, the house thermostat can be set anywhere but the signal to the unit is stopped by the exterior thermostat until it reaches its set temp.
