Alex Carr

Hello Jamesessex - I'm not going to blind you with ashp science as I'm no expert in this area, but I want to say one general thing. We have a Vaillant ashp powering ufh in a basement floor and vertical rads upstairs plus heating for hot water. The rads heat up quickly and we are happy with their performance, but the ufh is by its nature slow and takes near half a day to entirely heat up our spacious basement (heatmiser thermostats in each basement room) - everything I've read says low and slow if you don't want to get nutted with heating bills. That appears to be how it is with ufh, low and slow but ultimately effective. I will add that our property is 200 years old and we did an extensive retro-fit with regard to insulation, so there is relatively little heat loss. The minutae of running an ashp economically and effectively is, in my humble opinion, a steep learning curve which requires expectations to be re-tailored.

Thanks for that information John, but it will take a bit of time to get my head around what you are saying as it is not entirely comprehensibe to me. The installation company have been no help at all in helping me understand how to achieve the optimum running of the system. (There's a significant learning curve which I'm only just taking tentative steps to negotiate.) I would like to study the contents of your reply and, if it's agreeable to you, ask you some Q's. We'll get our first month's bill in a day or so and we'll see how our untutored use of the system pays out - if I can re-calibrate the workings as you are suggest the second month's bill should reflect a more economical set-up.

Yes, have a buffer. Weather compensation? I may be wrong, but I presume you mean that when the outside temperature falls below a certain point the heating kicks in; yes, the system does this. Yes, timed running slots for heating. More Q's?

I won't mention the name of the company but installing and set-up of a Vaillant ASHP to provide heat for ufh downstairs, vertical Stelrad radiators upstairs plus domestic hot water, has been a saga I would not like to live through twice. Here's my query: I understand how to programme the UFH & DHW, and they seem to be working ok, but operation of the rads seem only controllable by valves fitted to the base of each rad (there are 4 + an unprogrammable thermostat in each of three rooms). I don't get the relationship of the rads to the rest of the ASHP system - do they operate solely on the basis of their valve settings? (1 -5; the temperature range of these settings is not obvious; I have to corelate the valve setting to the temp settings on the wall-mounted thermostats to see what level of heat the rads are generating. Currently the UFH doesn't turn on until 6 a.m. each day but the rads are going during the night, and I sure as hell don't want that - is there a way of getting control of these beasts above and beyond the valve control on each rad? Enlightenment would be hugely appreciated.

Everything I read said that 8:1 using sharp sand was the proportion to use. No deviation from that from anywhere

Dry biscuit screed - 8:1 w. sharp sand - laid 22 days ago. Leaving it to dry out for another 22/23 days on the basis of 1mm per day drying time. Then will lay 15mm engineered wood flooring across the battens embedded in the screed. I don't know what the texture of the screed should be like after this drying out period because right now it's crumbly and is not setting in the way, for example, a semi-dry 4:1+0.5 water based screed would. Am I right to worry that the screed will not harden; or am I just needlessly anxious? Some input on this subject from a more knowledgeable member would be really appreciated.

I'll have to read up a bit on that to help me decide whether or not to do it. Also I'll see what the tiler says.

Having laid the screed the flooring contractor is now out of the picture. It was my contractor who screwed down the battens, much to my surprise. He's sensible most of the time, but he did mess this up; still, sins are there to be forgiven. He has a lot of work to do still on various other things and he will open all doors and windows during the day, shut them when it's time to go home and will leave the dehumidifier on overnight. As I said in my original post, there are five rooms and a hallway which have been screeded. I will wait 50 days for a 45mm thick dry screed to lose it's moisture and will periodically check the RH with a meter. Before laying decoupling mats in the 3 tiles rooms, I will seal the screed - any tips or advise on that?

Yes, that's my plan. Dehumidifier left on and check the RH every few days.

I think patience is the thing. 1mm per day drying time + dehumidifier left on overnight when the contractor & his crew are not there. Dry out the battens & screed, lower the rel. humidity levels... and anything else I can think of. Correct: no MVHR. The property is the bottom two floors of a 200-year old, 4-storey Edinburgh Grade II listed building. A f*cking nightmare to renovate but my wife insisted she wanted to buy the place because it is spacious like no other place we saw and it has a 30m long, 8.5m wide garden.

I'm calculating 1mm per day. Also usue of a dehumidifier to reduce the rel. humidity. Anything that wil help.

I think not as there's no way of knowing how close the battens have been fitted to the ufh pipes; it would only need one slip with the saw to cause irreversable damage.

Thank you for that Nick. I confess I am a worrier and a believer in Murphy's Law, that anything that can go wrong will go wrong. Everything I've read says 1mm per day drying time, though 2mm sounds appealing.

Thanks for that. I suspect that is what I'll do.

1mm thick steel plates? What is the function of the plates? And then tiled over that?