We recently had an Aira chap round, (long warranty). Told us a 6kW ASHP would be ok. We're not eligible for a grant because the previous tenant had one installed (even though the grant was £750 over 10 years ago). (We removed the 2012 ASHP—it was a noisy machine, and we’re after something quieter and more efficient - (is this the right thinking?) it's still in the garage).
My partner is all for buying new (with a long warranty) I'm up for taking a chance as there's some good value machines out there. - What system would you have if you were to do it again ?
Current thinking is 2 zone 60ish m2 under floor heating 16mm pipes 100mm centers + radiators up stairs - aiming to have a low flow temp and take advantage of the thermal mass of the thick walls and floor
Looking forward to hearing your thoughts, especially considering the low flow temperature target and potential ASHP options (new vs used) - what should we have on our shopping list - ?
Background
We bought an old (1850 stone built ) drafty damp house with an ASHP that needed a complete overhaul / insulating / damp problems solving... it's been quite a journey but we now have windows.. so thats nice..
Current Setup Plan:
Heating Zones:
Ground Floor: ~60 m² underfloor heating with 16mm pipes at 100mm centres.
First Floor: Radiators.
Aiming for a low flow temperature to maximise efficiency and leverage the thermal mass of thick stone walls and the floor.
Heat Loss Calculations:
I did some rough heat loss calcs based on U-values from ChangePlan's U-Value Calculator.
Heat Loss Breakdown:
Area
m²
U-Value
Temp Diff (°C)
Heat Loss (W)
Extension Walls
44
0.179
25
196.9
Stone Walls
48
1.26
25
1512
Windows & Doors
20.38
0.82
25
417.79
Old Roof
71
0.14
25
248.5
New Roof
34
0.147
25
124.95
Old Floor
56
0.22
25
308
Extension Floor
29.8
0.163
25
121.44
Total Fabric Heat Loss
2929.58 W
Ventilation Heat Loss:
Volume (m³)
ACR
Constant
Temp Diff (°C)
Heat Loss (W)
365.5
1
0.33
25
3025.46
Total Heat Loss (including 20% buffer):
Fabric: 2929.58 W
Ventilation: 3025.46 W
Total: 7364.44 W (7.36 kW)