Chicago zone 5
Slab is insulated with R10
Foundation walls are also R10 on the outside
1700 SF basement (7 feet down)
Heat load on home is approximately 60k
Getting a 19 or 21 seer heat pump from Carrier
5k PV system on roof

Electric cost here is $0.13
Gas is $01.2/therm

I am curious if gas or electric is the way to go. HVAC guy is recommending electric. I'm not sure how to figure out the best choice. Interested in opinions.

Found this site:

http://www.hearth.com/econtent/index.php/articles/fuel_cost_comparison_calculator/

Looks like Electric is about 2.5x the cost of gas per energy unit. However a gas boiler is much more expensive and from what I understand overkill for just a slab radiant and nothing else. Plus if the unit costs $2k more and has potential issues due to modulating down to a minimum, perhaps electric looks better?

This is almost no-brainer territory. At a nickel a therm gas is far and away cheaper than electric on operating costs- more than an order of magnitude cheaper.

But I'm going to assume that's really 50 cent gas, not not 5 cents.

In a 95% condensing burner (say, a condensing water heater or something) you get about 95,000 BTU out of a therm, so it takes 1,000,000/95,000= 10.53 therms/MMBTU of heat delivered. At 50 cents a therm that costs you $5.27.

In an electric boiler you get 100% of the energy content delivered to the water, which is 3412 BTU/kwh. So it takes 1,000,000/3412= 293 kwh /MMBTU.

At $0.13/kwh that's $0.13 x 293= $38.09/MMBTU

That's not an order of magnitude difference, but it's almost!

But really, what is the calculated heat load of just the basement, and how are you planning on heating hot water?

The installed cost of hydronic systems is pretty high, and if you're bringing gas into the house JUST for this application it's probably going to be cost-prohibitive just on up-front cost. Even if heating the slab with electricity, it's not clear that hydronic solution is going to be the "right" solution. (Low voltage mesh would have the same efficiency, and would probably have a lower installed cost.)

But it's also not clear why/how a heated slab is a better solution than a 3/4 mini-split or a zone off the the ducted heat pump. R10 is WAY underinsulated for a floor heated with 13 cent electricity, but might be financially rational for 5-cent gas (or even 50 cent gas.)

Hmmm, seems you edited the cost of gas since I started my reply. But the answer is still the same.

Your heat load in just the basement is probably well under 10,000 BTU/hr, which is within the output range of an electric tank hot water heater. You would never buy a gas fired boiler for a load that low, since it's guaranteed to be oversized by 3-10x.

But without the heat load number there is no way to give the right advice here.

Yes post was edited. I messed up it is $1.20/therm here. So it's $23 vs $38/MMBTU. Still in favor of gas, but the initial costs are high. I have gas and electric run to the equipment room. The floor is already PEX (poured yesterday). I honestly don't remember the basement load. I used HVAC Calc software at the time and have the report but it shows itemized listings for windows, roof, walls, etc. not basement, first floor, second floor. There is a line item for "Floors" showing 3300BTUH. This might be the basement slab.

R10 not enough? Really? Everyone here commented on how they've never seen so much insulation used before. I thought I was putting in enough.

As far as "if a heated slab is better than minisplits" - if you don't want to see a unit, nor listen to it, nor have movement of air, slab is preferred.

DHW is going to be supplied by a water heater.

I think you answered my question, electric boiler is the way to go in a choice between gas/electric boilers. Or should I use a beefier hot water heater...?