How much extra is the hyper heat compared to the non-hypo?

If it's not that much extra in cost, I'd say go for it. You're not removing your hydronic system. See how it goes, see how you like it, see which costs more to run. You can likely run both at the same time, with your hydronic to even out the cold nights during cold spikes.

If the cost is a lot extra, you'll likely end up (boston weather wise) running the heat pump mostly when above freezing temps, boiler below. Still likely a net win.

Running costs of the heat pump - i.e. which is more cost-effective - will mostly be driven by the cost differential between gas and electric (which may also be different at different times of day, depends on your utility) - i.e. not so much the absolute price of each. Gas is cheap in most places now, but that may not be forever.

I am actually thinking of going the other way. I have heat pumps but they are very expensive in heating up the house and noisy. I am considering adding hydronic base boards. What was your experience?

Why are the heat pumps expensive to operate? Do they have resistance heating supplemental heat?

No, they don't. But they still take up quite a lot of electricity. I measured around 0.03kWh consumption per sq ft per day (8 ft ceiling) for a well-insulated new construction home when the temperature is set to 70 and outside temp range is 40-60F.

The other problem is that since the inside unit is installed closer to the ceiling it blows hot air downwards, but that air promptly rises and gives a cool feeling near your feet. Overall it feels very uncomfortable.

I am thinking out loud a bit here but: you might consider a ceiling fan. In heating season, set to draw air up, at low speed (and possibly adjusting where the minisplits direct the warm air). The idea is cool air is drawn up, forcing warmer air down outside walls, and more consistent temperature throughout, including less feeling of radiant cool from cold surfaces. Can't say how much it would help in terms of comfort but I can say this for sure - would be a lot less expensive up-front cost and easily reversible if you don't like or can always just leave it. To me would be worth trying for a hundred or two bucks. A lot less than hydronic baseboard.

(It won't directly lower heating costs but if you are uncomfortable at a given temperature, it's likely you're setting temperature point above what would be needed if more even throughout)

Good point. I had thought of that too, but the problem is that 8ft ceilings are quite low for ceiling fans. I will try it in another area where I have 9ft ceilings.

Hydronic base boards are expensive if you compared to the ductless heat pumps. the diversion of air is equal and consumption of energy is less.

are you referring to installation or operating costs? I am considering using solar to offset the operating costs. I don't have a quote yet on the install.

The other problem with baseboards is the aesthetics.

"DH loves the idea of using mini-splits for all our heating needs and lessening our reliance on fossil fuels."

Ever wonder where the electricity to run your "Green" mini-split comes from? Yup, a fossil fuel-fired power station!

In USA solar makes up less than 2% / Hydro less than 7%... (mostly hydroelectric?)

Hi, We will have both systems in place once our project is done. They complement each other well and we needed a/c