why the UK is pushing do hard for air to water is a mystery to me.
I was a little confused when I followed a European forum. The transition to heat pumps has been a big deal, lot of discussion in the UK and Germany. It had a bunch of people talking about boilers and having heat pumps heat water, which confused me. I’d only heard about boilers in the US much in the context of large buildings with old steam heating systems.
In the US, I’ve seen plenty of air source heat pumps. Some water source heat pumps. But they both are used to heat (or chill) air, which is then blown into ducting and circulated through the house. Provides ventilation and such and humidity control. But it seemed to be overwhelmingly the case that people in Europe were talking about heating water and circulating that.
Small window or through-wall air conditioning units do obviously heat air, usually for one room. Split minis move refrigerant, which ultimately heats or cools air.
And it seems like you’d rather have ducting, as it can provide control over a given ratio of fresh air to an area of a building and filter it.
I was able to find a few companies in the UK dealing with ductwork, but they focused on new office buildings.
I eventually figured out what was going on.
A lot of houses in the US were built after the introduction of air conditioning. Not only that, but the US has more areas that get quite hot than Europe, so once air conditioning was an option, people really wanted it. The result is that a lot of US housing was built with central air conditioning.
This meant that when houses were designed, ductwork was built into the design.
Ducts are relatively-large. It takes a lot of space to move a given amount of heat.
It is not easy to retrofit ducting into an existing house. You have to have this big thing jammed into the house somewhere that runs to all rooms.
Water is much denser. If you use water to move your heat around, you don’t require that much space. So if you retrofit an existing house, you don’t have to mess the house up. Not only that, but a lot of buildings in the UK had apparently already been set up with systems that heated water with natural gas and then moved it around the building to heat it, so putting in a heat pump could use that existing system.
My guess is that people did the math and decided that it didn’t make sense to massively go rip up existing houses when they could stick comparatively-unobtrusive additional water pipe in.
My guess is that what will happen is that new buildings will incorporate ductwork, so there will be a very slow transition to ductwork. But it won’t happen overnight, just as buildings age out and are demolished.
The current transition to heat pumps that they’re doing is on a much shorter timeline than that.