The issue is that the original radiators were sized to move the necessary n kW into the room with a water temperature of 60C. If you drop the water temperature to say 45-50C, you're only going to get roughly two-thirds of the heat transfer. The other third needs to be made up somewhere else - additional heating or better insulation.

And btw: you don’t need to reach 60°C with a heat pump. That would be pretty inefficient.

Thanks for the feedback.

My boiler gives me control of the temp of the water running through the radiators which is independent of the room air temp thermostat. I set the water to ~55°C which seems to reasonably get the air to 17° without running continuously. I mentioned 60° because I figured that temp would enable someone to heat their room up quickly. I wonder why you say a heat pump would not need 60°. I would think the radiators need to reach a high temp like ~50—60° regardless of the kind of furnace. Maybe I’m doing something inefficient. Should I use a lower temp? I could lower the water temp but then there would be a point where the furnace has to run continuously which i would think is inefficient. I’m not sure how to find the efficiency sweet spot.

UPDATE

That pricetag is just the unit and standard installation probably. Pieces are crazy high Here in Germany because the demand is crazy high. Not many heating installers have made the additional qualifications, so those who did can demand practically anything.

Sounds reasonable. So if the demand has out-stripped supply on heat pumps, I wonder if geo-thermal would actually be cheaper than a heat pump ATM. IIRC the digging would be ~€10k (what I think is a typical price for digging a well.. could be off). Though I don’t suppose you could use wall radiators with geothermal. Since geothermal water is only ~6° warmer in the winter, hydro-radiant flooring would have to be installed.

The other one is that a lot of people presume a house needs state of the art insulation, which obviously costs a lot to retrofit.

However in nearly all cases the old radiators work just fine with a heat pump as does the insulation. Underfloor heating and more insulation would make it more efficient, but that is often not worth the money, unless you do plan to do it anyway. When you redo the floors you can then add underfloor heating. Same for insulation, once you redo the roof or have to do work on the walls.

Tiny house = very tiny and probably new and well insulated.

Estonia also likely has very low labour costs and less difficulty finding staff.

Hydronic systems are usually in the >15kW range, and often have split indoor and outdoor units so you need to both do the refrigerant piping between indoor and outdoor, and the water piping to the radiators. Many systems also include domestic hot water heating as part of the same system, so three separate sets of plumbing.

In most of the first world, purging linesets, vacuuming, and releasing refrigerant is usually ~$500.

I worked in the industry and real-estate.

These houses were never designed to be insulated or airtight, and (controversial take) IMHO often shouldn't be fully insulated. I lived in a larger old house, and we'd heat a limited amount of rooms. The rest of the house was largely unheated and not properly insulated, allowing moisture to come and go. You simply dress accordingly. That's why people were always wearing multiple layers and three piece wool suits back in the day.

Eg. some old houses use lime mortar instead of cement. Lime mortar is more porous than cement, so it absorbs and wicks moisture. If you insulate that improperly, you're asking for problems, because moisture will build up behind the insulation or get absorbed into it.

Same thing for the roof of an old property. They were designed to circulate air. Water gets under the tiles, the wooden structure get damp, but it's not a big problem, because the air and moisture can evaporate and escape. People will poorly insulate their roof, then end up with disastrous moisture/rot issues, resulting in very expensive structural damage.

TLDR: If you insulate these properties improperly, the chance of rot or moisture issues is not negligble, and arguably you should ask yourself if it's even a good idea to insulate at all, rather than simply adapting your lifestyle and heating a limited amount of rooms.

Cavity filled insulation is very common and relatively cheap. I know people who did it themselves with an expanding foam gun and multiple cases of foam.