[SDMCF]

Originally Posted by AC_Hacker

A GSHP is pretty much the most economical form of heating you can have. But it is not like running you are going to run GSHP right into your ordinary house heating system and expecting everything to work just like it did before, only cheaper.

and

You can't use the methods that worked for heating with wood, coal, gas, oil, etc. because these methods produce much hotter temperatures than a GSHP is capable of... things need to be done in a different way.

That's a reasonable rule of thumb but as always "it depends". I just installed a GSHP and connected it into my existing heating system (radiators). I didn't change anything inside the house apart from connecting the GSHP into the central heating pipework. Everything works just like it did before, only cheaper.

One of the most important things to bear in mind is that a GSHP will produce hot water at a temperature of 120F max.

That is indeed the crux of the issue, although I would say 55C/130F. My GSHP manual claims 65C/159F but I don't believe that. My radiators run at a maximum of 55C so I just about cope during really cold spells, but of course usually it is not so cold and the radiators don't need to be so hot.

There are three big things that can lower the required water temperature:

1. Minimize the heat loss in your heated space by reducing the infiltration (air leakage) to the very minimum.
2. Increase the quality and quantity of insulation significantly above the required code level.
3. Insure that your heat input method, forced-air or water heated radiating panels, are as efficient as possible.

Maybe a 4th option is to install more radiators (or whatever you use).