Mini Split or Radiant or both?
So I am located in northern Utah remodeling a old brick Ranch house the walls are lath and plaster with no insulation I don’t really want to demo walls. I will replace windows doors and beef up insulation in attic and air seal where I can. I want to finish basement as well about 2000 total sq. ft. I would like to get rid of the old furnace and all the low hanging ductwork in basement. At first I wanted to do hydronic radiant heat in the joist bay insulate joist bay then do a 2nd radiant zone below insulation to heat basement from the ceiling as well. But I wanted cooling also so I thought I would put two ceiling cassettes in attic to cool main floor. Now my question is if im going to run a mini split should I just forget the radiant and add a few heads in basement? My issue is cost to operate I’m unsure the cost of electric hyper heat mini’s vs the operating cost of natural gas? A lot of people say the mini will be twice or three times as much to heat but when I run numbers it seems comparable. Does anyone have real numbers or done something similar to help me in my decision? Thank You
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Replies
While you're add it you should also price out adding insulation to the walls!
Every house is different, there are no standards or "rules of thumb." Energy prices vary dramatically by region so there's no fixed answer as to what fuel is cheapest.
Have you been living there a while? Do you have records of how much you've paid to heat the place? The best place to start is this article which tells you how to size a heating system based on past fuel usage: https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler
Then go here and look up the heating and cooling design temperatures for your climate:
https://www.energystar.gov/ia/partners/bldrs_lenders_raters/downloads/County%20Level%20Design%20Temperature%20Reference%20Guide%20-%202015-06-24.pdf
That can tell you how much cooling you need relative to your heating, which helps answer your question. If you need about the same amount of heating and cooling mini-splits are probably the way to go. If you need a lot more heating than cooling it might make sense to size the mini-splits for the cooling load and have supplemental heating to make up the rest of the heating load.
Then we need to know what the price you pay for electricity and natural gas is.
You can figure out the fuel costs with these equations - they both will give $/MMBtu.
Electricity with heat pump: $/kwh * 293 / COP
Gas: $/therm * 10 / COP.
I would be shocked if there's a fuel cost difference significant enough to justify installing the radiant.