You are forgetting that a heating system is sized for exactly those conditions (though usually -3C outside). It doesn't assume that the internal temperature has only dropped (e.g) five degrees. If the heat loss calculation says you need a 15kW boiler, you need a 15kW boiler;.fitting a 30kW will not achieve anything. But if you have a combi which produces 30kW for heating, then range rating down to near 15kW would be a sensible thing to do.
This is such an interesting conversation, and much appreciated.
From my (limited) understanding, my property's heat loss, is calculated at an external temp of -3C and in internal temp of 20C. Let's say for example the total is 13kW. My boiler will need to run, on average, at 13kW to maintain this constant internal temp of 20C, assuming all other factors, including the external temp of -3C remain constant.
But if we now consider the conditions I outlined above namely: -5C outside and -5 inside — due to leaving the house empty and unheated during a 2 week cold-spell. With this scenario, when I return from holiday, I now wish to heat the house as quickly as possible to reach 20C, and so the boiler can ramp-up to 30kW, and then modulate down to 13kW when 20C is reached?
In practice, the boiler would only increase its output so the flow temp maxes to say 80C; and the radiators would be able to shed far more heat, as the delta is now D78 and not D50 (or even lower). (Av rad temp of say 75C, and an internal temp of say -3, gives a delta of D78).
Any thoughts? Is this a correct analysis?
Hence why, it seems, that when you have a modulating boiler, you don't need to range-rate it, and indeed if you did so, it would not make the boiler as useful and as quick to rapidly heat the house when you needed to.
Of course, I understand that in practice, you would be better to perhaps leave the heating on at a low-level whilst you are away for a number of reasons.
Thanks!
) why the boiler does that? What is it aiming to achieve?
