This is helpful -- we need to do a better job of guiding folks through a more complex set-up like you're describing. You're right that it's easiest for folks with centrally ducted A/C and furnaces.

If you're choosing 'multi-zone', "Heat pump: Number of units" corresponds to the number of _outdoor_ units, rather than indoor heads. For all other configurations, it maps to both outdoor and indoor (the others are all single zone). So, if you want to go with a multi-zone heat pump, I'd suggest entering 1 or 2 for "Heat pump: Number of units" (or just leaving it untouched, in which case the model will choose automatically based on home size).

> IMO you should just stick to calculate fuel costs for heat with gas, vs heat with electricity, and leave out the installation costs.

Roger that. We started out that way, and the cost-to-install was the number one thing that people asked us in follow-up questions, so we added some high-level guidance. I think the lack of transparency on upfront costs and pricing is a major issue for the transition broadly and a problem that needs to be solved -- that's high on our minds.

> That's really all I want to know: What costs less, heat with gas, or heat with electricity. Or maybe a hybrid.

Helpful! Related to the previous point, we want to make it easier for you, with a proposal from a contractor in hand or existing equipment already installed, to choose that equipment from among what we're analyzing (rather than only seeing cost savings for the most efficient unit that we choose automatically). In your case, you'd then be able to see exactly the cutoff points when your existing fossil fuel equipment is (a) necessary because of reduced heat pump capacity at lower temperatures, or (b) cheaper to run than the heat pump. FWIW, (b) is far rarer than we thought going into this exercise.