Hi folk, I'm in the process of sizing up central heating requirements for my house. Just to give you some background it is a 3-bedroom semi detached house built in 1957 with upvc double glazing and wooden floors upstairs and down, topped off with 100mm of insulation in the loft.
The plan is to fit a system boiler in the loft, connecting it to the existing HW tank, which is also served by solar panels via a separate solar coil. I have spent a long time deliberating the pros/cons of this approach and this seems to be the best option.
I have carried out heat loss calculations and the CH requirement came out as 13.3kW, based on being pretty generous (rounding up to the nearest half meter, not deducting chimney breast area, adding on 15% for north-facing rooms etc).
If I add on 2kW for the HW requirement, and 10% for overall losses, the total figure is 16.8kW.
My boiler of choice is the Vaillant Ecotec Plus which comes in various outputs including 15, 18 and 24 kW. In my eyes the 18kW version is bang on the money. My only worry with choosing this option is the possibility of future expansion (perhaps adding a single-storey extension to the back of the house which will increase the heating requirement by, say, 3kW), or the fact that I may not have added sufficient "leaway" in my calcs.
Could I ask if you think the 18kW is a good choice given the figures above?
Thanks in advance Luke