What? Electric baseboard are rightly on the out, because they cost a fortune to run.
Water based gas radiators are absolutely not cheaper to install in the us than forced air. They are uncommon and expensive. Heat pump forced air is slightly more expensive to install than heat pump forced air. The a/c part is basically “for free” these days
You're missing the point, obviously water based gas radiators are expensive in the US, because almost nobody uses them.
We're discussing how certain changes in the last 100 years contribute to overall housing costs.
If something has become ubiquitous it might be more expensive than to just go along with the flow for any individual house, e.g. I'm sure most new housing plans in the US are designed to account for running HVAC ducts.
Instead you need to look at what e.g. a typical house in western Europe is spending on the heating system as a percentage of overall construction cost.
I don't know that offhand, but I'd be very surprised if it even reaches 2%, whereas apparently US HVAC systems cost 6%.
A 100 meter roll of aluminum coated PEX pipe is around €100 (all you'd need for a typical house here). You can run it directly through structural beams (only requires around a 20mm hole). The rest is just the central gas burner (maybe €2000) and some radiators at say €150 a piece. If we very generously call that €5000 with plumbing/installation that's 1% of a €500k house.
Water based gas radiators are absolutely not cheaper to install in the us than forced air. They are uncommon and expensive. Heat pump forced air is slightly more expensive to install than heat pump forced air. The a/c part is basically “for free” these days