Temp. efficiency question between Mr. Slim and in-floor electric radiant heat
I have a newly built 1008 sq. ft patio home (on slab) in central Minnesota.
I have a Mitsubishi Mr. Slim split heating/cooling system, outside unit is model MUZ-FE18NA and inside unit is model MSZ-FE18NA. I also have a single zone in-floor radiant heat system powered by an Electro Industries 9kw mini-boiler.
My Mr. Slim operator manual shows the lower limit for heating using this model is -13F dry bulb and -14F, and that my unit puts out 100% of rated heating capacity at +5F and 80% of rated heating capacity at -13F.
I have lived in the house for a year now and absolutely love the Mr. Slim! It's super quiet and efficient and has done what I've asked of it so far.
My question is in regards to "heating" using the Mr. Slim with the cold temps coming. We can have some brutally cold winter temps here in MN, and I am looking for recommendations as to what temperature would be a reasonable point to stop using the Mr. Slim for heat and start using the in-floor radiant heat?
I should also mention that I am on a "dual fuel" program with my electric cooperative that sells me electricity for both Mr. Slim and radiant boiler at the exact same half price cost of 4.2 cents per kwh.
I am receiving some mixed signals so far, with one saying to discontinue use of the Mr. Slim at +20F and others saying that because of the efficiency of the Mr. Slim, that I would be best served to continue to use the Mr. Slim down to the -13F temperature. That's why I'm posting here to get the views of pros in the field.
Any recommendations would be much appreciated as well as pros and cons considerations (wear and tear on the Mr. Slim at sub-zero temps, mold potential, etc.) other than just the cost of electricity.
Thanks in advance very much for your replies!