Has anyone had any experience with getting their rental property up to the so-called "healthy homes" standard?

On the one hand, the HHS says: "Landlords must have enough fixed heaters installed so that a whole living room can be heated to 18 degrees, even on the coldest day of the year.

And then you get this "tool" that takes you through a very complicated calculation where you have to calculate the size of each wall, the windows, insulation - everywhere ceiling, floors, walls etc. And then it spits out this answer that says you need 7kw of heating to heat that space.  What a load of BS!!!

This is a 1940's house that we renovated and have lived in for 7 years, and have now moved out and will be renting it. So we had insulated it up the wazoo, and were well able to get the room to a constant 18 degrees+ - actually more like 20-21, using a 2.4 kw 3 bar radiant heater. It has a thermostat, as required, and cuts off when it reaches the desired temperature, then just clicks in when needed. I have also since then also retrofit double-glazed all the windows so am very confident that it will be etc etc. On VERY cold nights, we have occasionally boosted with an oil-filled heater.

Hope that wasn't too much of a preamble, but I am as frustrated as hell being faced with putting in heating that I know will be way overkill for the space. So can anyone advise if they have had a similar experience and how did they deal with it?