Condensing Boiler Rating vs. Old Boiler

[andrewla]

When we moved into our house in July last year the existing Potterton Netaheat 16-22 had died. In September we had a new system fitted incl. tank with new controls, motorised valves etc. The boiler fitted is a Vaillant EcoMax PRO 18E condensing boiler.

Last week our kitchen was completed and a new radiator fitted. Lots of problems getting it running and even now it takes all evening to get the radiator really hot. Otherwise the system has seemed fine although in the very cold weather before Christmas it sometimes took a long time to get the house warm. We have a mid-70s 4-bedroom house with 12 radiators (incl. new one).

The kitchen fitter/plumber calculated our radiator values and came up with 60,000 BTUs, added 10% for standard warming up times and 7,000 BTUs for the hot water to give a total of 73,000 BTUs. When I checked I realised the boiler (sized by the corgi guy) is actually a 61,000 BTUs output boiler.

My question is should a boiler of at least 73,000BTUs been fitted e.g. an 80,000 BTUs output boiler or are condensing boilers more efficient and therefore a smaller size be used? We may eventually add a conservatory with 1 or 2 radiators and want to have enough headroom for the boiler to cope. Should he have fitted the bigger 28E model which is rated as 96,000 BTUs?

 

[chrishutt]

Sounds like your boiler is undersized. The output is whatever it is, regardless of the efficiency of the boiler.

Your boiler is just a tadge low for the heating load, but doesn't allow any extra for the DHW load. You can get round this by timing your DHW recovery periods to be outside the heating periods.

Bear in mind that the problem may be something different to an undersized boiler - sounds like the circulation isn't balanced properly.