I am currently in the process of a refurb of a 20 year old house, its off grid and we have just replaced the old LPG boiler/tank with a 16kw Midea ASHP. I am installing a 60mm PIR insulation board (possibly thicker, depending on floor screed choice).
We have striped the ground floor back to block & beam, new extension also has block & beam.
A lot of people have recommended a gypsum based anhydrite floor screed, I come across these alot (work in the flooring trade) and ideally would like to avoid these if possible. Main reason is their laitance, moisture retention when first laid etc. My thinking was I would buck the trend and go for a "traditional" sand and cement floor screed, creating a bigger thermal mass, maintaining a more even temperature and probably a more constant flow temperature from my ASHP.
The argument for anhydrite screeds is better thermal conductivity (e.g. quicker to heat up) but cement based screeds are known for retaining the heat for longer.
My thinking was a cement based screed at 60/70mm would be easier to maintain over winter when temperatures drop below zero (typically at night) and I could keep the ASHP running on a lower temperature to maintain a decent floor temperature. As opposed to the anhydrite screed which would more than likely reach its desired temp much quicker, cut the pump out then cut back in again as it needed to etc.
My thinking of course on the thermal performance is pure speculation, but would appreciate feedback from others and how happy you are with the floor screed you have? Is anyone running a 60/70mm sand/cement floor screed with a ASHP, how do you find it?
