Hydronic radiant thermostat

[birchlake]

I'm very familiar with the -FE18NA, even had one installed at my mother's place last year, and they're one of the most popular units for heating Net Zero Energy homes in New England as well as other high-performance houses. A friend installed three of them on a 3-family that I helped him do a deep energy retrofit on last year. They are reasonably "smart" units, and designed to take it at low temp. As I understand ti the automatic shut down at about -18F is to self-protect from damage related to mechanical tolerances of the metals in the bearings and compressor. They have modulating internal resistance heaters to keep them in mechanical spec, but not enough to run the at any arbitrarily low temperature. I have no issue with just letting them bounce off the bottom of their spec rating, since they're designed to self-protect. I believe Daikin has similar cold-temp auto-protections built in, but I don't know at what temp they kick off. If they work for central ME and northern VT (where excursions below the self-protect temp are common enough) they'll work in Melrose MN. (IIRC BadgerBoilerMN has an FE18NA too, but only uses it primarily for air conditioning, his being a hard core wet-head & all. :-) )

You're not really losing efficiency by letting an electric boiler cycle, and mechanical stress & degradation from thermal cycling isn't really all that much either, at the temps you're talking. How often does it cycle during the shoulder seasons at the 114F setting, and how short are the "on" cycles?

Dana,

I really like my Mitsubishi mini-split. The only issue I've had with it is a bit of a rhythmic ticking from the inside unit that was an annoyance. Ended up having to put shims on all corners of the inside unit to eliminate the vibe/tick. Other than that, it really works well for both heat and air conditioning, along with being very energy efficient as you mentioned. And you can't even hear the thing run outside; can't believe it is that quiet! Next winter, I will try experimenting with running the Mitsubishi a little deeper into the colder temps to find my comfort level with it before I start relying solely on my in-floor heat.

As for cycling of my Electro Industries boiler, when the outside temperature is in the 20s and 30s, it doesn't actually cycle that often at 114F, maybe every 8-12 minutes or so, but what I found weird is that when it does cycle on, it (sometimes) only runs for 1-2 minutes, then cycles off. I haven't tried it at 102F in this weather, but am thinking about trying 102F and observing how long the cycles are at that temp. As you mention, with solid state circuitry the wear and tear on the boiler is minimal, and although the boiler contactors are racking up a few more cycles at the higher temp setting, I would think the contactors are possibly rated for millions of cycles?

I just wondered which boiler temp setting would be the best compromise for boiler efficiency and reliability and energy efficiency. But sounds to me like it might be six of one, half a dozen of the other?

Thanks for the advice guys.......making the turn from "forced air" to hydronic in-floor and mini-splits has been a learning experience!! (but a good one)