Advice on ball park radiator sizes please
Posted by: @derek-mI'm afraid that I do not follow your logic, since heat loss is heat loss and is not dictated by the radiator size or type. Different size or type of radiators will merely require a higher or lower water temperature so that the thermal energy output matches the present heat loss.
Sorry, I obviously didn’t explain that very well, and wrong to boot. As you say, the room/house heat loss is fixed and determined by the fabric and outside temperature, etc. the radiators would then be chosen to provide that output at the desired flow temperature and flow rate, again as you state. I was speculating that the values might be for the standard 50C but without checking the actual radiator specifications and so misled myself on the figures, the Stelrad k3 700x2000 for instance looks like it outputs 5424W at delta-t 50 according to the data sheet, which is considerably higher than the values given. Please ignore my mistaken intrusion.
Thank you all - so grateful for your advice.
I went back to the company, and they forwarded my query to another branch (the original person being away for 3 weeks). The person there confirmed there was an error - apparently the original guy had read the wrong column of figures or something...
So I now have a revised set of sizes, which are much closer to what I anticipated:
| Room | Watts required | Suggested radiator | Radiator type | |
| 
 | 
 | 
 | 
 | |
| Living room | 
 | 
 | 
 | UFH | 
| Shower room | 
 | 
 | 
 | |
| Kitchen | 
 | 
 | 
 | |
| Dining hall | 
 | 
 | 
 | |
| Hall | 
 | 
 | 
 | |
| Landing (1st floor) | 700 | 600x600 | K2 | |
| Study | 1050 | 600x600 | K2 | |
| Sitting room | 1600 | 600x1000 | K2 | |
| Bed 1 | 1500 | 600x1000 | K2 | |
| Bed 2 | 1600 | 600x1000 | K2 | |
| Bed 3 | 1550 | 600x1000 | K2 | |
| Landing (2nd floor | 700 | 600x600 | K2 | 
Somewhat different to the originals!
I would suggest that you ask the company to provide a full set of heat loss calculations for your home. Also ask them to clarify what is meant by 'Watts required' in the table, and to confirm their calculated Leaving Water Temperature (LWT) coming from the heat pump.
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