Edit: Oh actually, I was wrong.(and I guess it makes sense. It would suffer the same problems as an electric hybrid) There is no hybrid gas heat pump for hydronic heating. Basically my entire city is hydronic heating so heat pumps are not an option. However
a bunch of my neighbours have heat pumps and I suppose it’s just heating one room in their house and it’s not even connected to the thermostat of their hydronic heater in any way.. Seems pretty silly to me. At least you get an air conditioner out of the deal so that you can use more electricity in the summer.
You can then make your own hybrid with a resistive electric boiler or a gas boiler wired to second-stage or emergency heat.
My 1920s house with radiators and terrible insulation outside of Boston runs with return water temps in the low 90s in shoulder season and 120°F when it’s 12°F outside, using outdoor-reset/weather-compensation.
Those return temps are entirely compatible with air-to-water heat pumps. (And result in 22-24 hour run times per day, which makes for extremely comfortable heat, despite the generally lacking insulation.)
I don’t have one because HVAC contractors are living in the 1990s and want to do a 3-hour, 2-person combi boiler install for $10K in profit rather than think through how to do anything unusual.
