I need to buy a new boiler and am planning to get a Valliant system boiler. My house is 4 bedrooms with two bathrooms and a separate WC. Upstairs we have 4 radiators with TRVs, one radiator without a TRV and one towel radiator. Downstairs we have one radiator and then underfloor heating covering approx 100 square meters. I am not sure whether to buy the 30kW or 37kw Valliant EcoTEC plus boiler. I’m getting an unvented cylinder probably a 250l Joule cyclone. And planning to add an accumulator too, maybe 300l.Any advice would be greatly appreciated. Thank you!!!
Are you a tradesperson and able to answer this question?
This is a massive oversizing of your boiler. The maximum size you would require is 24kW. Underfloor heating requires a heat input of 1kW per 10 square metres and radiators and hot water cylinder roughly 2kW each, not knowing what size they are, giving 22kW approximately.
Also not sure what you intend to achieve with the accumulator unless you were thinking of adding solar panels to your system.
37kw would be excessive for this size installation and 30 is more than adequate. Still over requirement but the radiators will reach temperature more quickly. A 250 cylinder is a good size cylinder. An accumulator will boost your water flow throughout your house provided it’s installed in the correct position especially if your incoming main is less than 22mm which is the ideal. Even if you have 22mm an accumulator will be of benefit especially in the event of both bathrooms being used at the same time, toilet being flushed while someone’s in the other shower etc. Essentially it’s an additional three hundred litres of water stored under pressure to help meet your demand if everything is turned on at the same time.
The property you intend to heat should be measured and surveyed to calculate the heat requirements to gain the best efficiency. Having said that if you are fitting a system boiler as stated then as a ball park figure 18kw should be adequate for your requirements, but without more information, ie No. of outside walls, U value etc this can only be taken as a rough guesstimate The main problem with over sizing the boiler is possible boiler cycling which can reduce efficiency .
