Combination boilers in a larger house

[John Wadden]

5 years ago I fitted a combination boiler in my house which is a large double fronted 1930's house. It has alsways struggled to cope, and would be running all of the time if I had all of the rads open. I used the system to plan for the rads and thought the 120,000 btu boiler would cope! Is it a fault of the boiler - the installation - or the system? How large do combi boilers go in output? Is there any way I could get independent advice from someone who doesn't just want to sell a new system to me? Thanks John - new user

[Christian McArdle]

The problem is probably with your insulation. Almost any combi boiler should heat almost any house. If it doesn't, it is cheaper and more environmentally friendly to address the insulation than increasing the size of the boiler. Ensure you have 300mm of loft insulation, you fill your cavities and draught seal any old windows, before even looking at the heating system.

Alternatively, you have misunderstood how most combi boilers work. Generally (but not exclusively) they have modulating outputs. This means that when you don't require the full heat, the burner runs at a lower setting and doesn't need to turn itself off and on periodically like an old cast iron lump would have. The only way to get it to turn on and off continuously is to reduce the heating load below the minimum modulation level, which will be a small fraction of the full load heat.

Christian.

[IMM]

It is probably giving 96,000 BTU/hr into the rads if 120,000 BTU/hr is input. Is it input or output? What were the heat loss calculations? What size boiler did it give? Does it do OK for DHW?

Many combi's will give full output to the DHW, but drop output for CH by about 1/4. What make of boiler? etc? etc?

[John]

Just a wild guess here but is your 120,000 BTU combi boiler an Ideal Reponse? I'd suggest you take a look at the specification for its heating output as opposed to its hot water output. (Hint - the heating outlet is nowhere near the magnitude of the hot water output)