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Community and Q&A

Programmable thermostat recommendation?

user-6258531 | Posted in Energy Efficiency and Durability on

My ranch house in Northern Idaho will have a natural gas fired in-floor hydronic heating system. I also added one zone mini split for A/C needs, but this could also make sense to run during shoulder heating seasons. I’ve installed a PV system that will produce excess power during most of the year, so at times the electricity to run the mini-split will be “free”. It gets complicated.

Any recommendations on a programmable thermostat to use with this set up? I can envision control algorithms using outside temperature and time of day.

FYI, I had no plans to add the mini-split, but forest fires this summer made the possibility of closing up the house for several days in the heat of summer a possibility.

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  1. GBA Editor
    Martin Holladay | | #1

    Perhaps a GBA reader will recommend a thermostat for your application. Here's what I would do if I were you: Set your ductless minisplit to 72 degrees F, and set the thermostat connected to your hydronic system to 69 degrees F. Let the minisplit do most of your heating -- until the weather gets so cold that your minisplit can't keep up.

  2. SwitchgrassFarmer | | #2

    Tekmar thermostats and controls could probably be described as the gold standard for hydronic heating. This company understands things like "outdoor reset" and floor sensing that aren't commonly handled by other thermostat manufacturers.

  3. Jon_Harrod | | #3

    With radiant systems, you're better off keeping the internal setpoint fairly constant; using setback thermostats can lead to temperature overshoots due to the high mass and time lags in the system. You can optimize boiler efficiency by varying the water temperature in response to outdoor weather using the Tekmar controls Andrew recommended. If you want the ability to control the radiant system and the minisplit through a single (smartphone-enabled) interface, I'd check out the Honeywell Redlink products, which are compatable with Mitsubishi minisplits as well as conventional HVAC systems.

  4. user-6258531 | | #4

    I will probably operate things manually as Martin suggested, using the mini-split as primary when I have excess electric credit or electric cost favors natural gas. My original question was to identify a thermostat that could automate that control between two sources and be remotely operated.

    I am ignorant about boiler controls. My boiler is an NTI TX51. It looks to me like it has outdoor reset and an outdoor temperature sensor, so would I benefit by having that capability in my thermostat?

    Perhaps I should have installed a floor temperature sensor. I can see how one might want to set a minimum floor temperature even when using the mini-split as primary heat source. At this point, my slab is poured but I haven't yet installed vinyl plank flooring over it. Is it still possible to install a floor sensor?

    I did not plan to use setbacks. The house has four zones. The mini split is located centrally to the kitchen/living areas. I have separate zone for bedrooms so we can keep those at a comfortable sleeping temperature all the time. The mini-split was an after thought more driven by the need to use AC during periods of bad air quality (forest fires). But now that I have it I'd like to wring the most value out of it.

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