I have to choose a new gas boiler for a very small 3 bed terraced centrally heated house. Full double glazing and 6” loft insulation.
I have a Y plan system.
I posted with various questions about this system recently but have got to the main question now.
I have been warned about oversized boilers being inefficient. The problem is that according to the size calculator on the IDHEE website I only need 4.2 kw to heat the house, not including the hot water allowance of 2kw, and I am confused about the relative importance of sizing the boiler, non condensing mode, short cycling, etc. A couple of other calculators I tried still don’t go above 6kw.
I am interested in something like the Intergas HRE 18 SB or OV, which modulates down to 5.6 kw
The Veissman 100 W compact would seem to modulate from 13kw max to 1/3 of that, ie 4.3kw.
Baxi have models that go down to 2kw to 12 kw
I understand that even with these low kw boilers, there will still be a majority of times in autumn and spring where even 2kw will not be required so even an exactly sized boiler will spend most of it’s time running inefficiently. Is this correct?
Can anyone explain exactly what would happen that ideally shouldn’t happen if I use the larger two, Intergas and Veissman boilers? From what I can see on the ‘net I am forming the impression that it is accepted for condensing boilers only to condense efficiently after switch on while the house is heating up. Is there a level of inefficiency at which the system worsens from non condensing due to return being too hot, to actual short cycling, and in reality do both these situations occur in warmer weather?
Incidentally on the SEDBUK boiler efficiency database, in the tables for gas boilers, the lower wattage figure that the boiler can modulate down to is not given, only the higher figure, which is displayed twice, ie "modulating (28.4-28.4 kw). I would expect two values to be given, the lower and the higher, why is this?
Also does anyone know how quiet these boilers are in operation?
I have a Y plan system.
I posted with various questions about this system recently but have got to the main question now.
I have been warned about oversized boilers being inefficient. The problem is that according to the size calculator on the IDHEE website I only need 4.2 kw to heat the house, not including the hot water allowance of 2kw, and I am confused about the relative importance of sizing the boiler, non condensing mode, short cycling, etc. A couple of other calculators I tried still don’t go above 6kw.
I am interested in something like the Intergas HRE 18 SB or OV, which modulates down to 5.6 kw
The Veissman 100 W compact would seem to modulate from 13kw max to 1/3 of that, ie 4.3kw.
Baxi have models that go down to 2kw to 12 kw
I understand that even with these low kw boilers, there will still be a majority of times in autumn and spring where even 2kw will not be required so even an exactly sized boiler will spend most of it’s time running inefficiently. Is this correct?
Can anyone explain exactly what would happen that ideally shouldn’t happen if I use the larger two, Intergas and Veissman boilers? From what I can see on the ‘net I am forming the impression that it is accepted for condensing boilers only to condense efficiently after switch on while the house is heating up. Is there a level of inefficiency at which the system worsens from non condensing due to return being too hot, to actual short cycling, and in reality do both these situations occur in warmer weather?
Incidentally on the SEDBUK boiler efficiency database, in the tables for gas boilers, the lower wattage figure that the boiler can modulate down to is not given, only the higher figure, which is displayed twice, ie "modulating (28.4-28.4 kw). I would expect two values to be given, the lower and the higher, why is this?
Also does anyone know how quiet these boilers are in operation?