[sokoloff]

Did they retrofit the linesets through the walls to the interior units?

Or do you have existing ductwork (which a house with hydronic gas heat probably does not have, or else they'd probably not be asking the question)?

[fullstop]

Yes, there is existing ductwork in the house.

I understand the situation -- I had searched to see if hydronic gas heating used ducts, and it can but it seems that this is not common.

Their issue is not an issue of heat pumps themselves, but rather the lack of an air handler.