Electric boilers are available in lots of versions and lots of output levels some – for example our new ctc ecozenith i250 model – have built-in hot water heating you can also connect solar heating directly to it using our two unique connections. Medium size house requiring up to 15 radiators will require an estimated outout of 28kw to 34 kw. Know your rights - home appliances. But what size of boiler will best fit your needs? if you live in a flat or a terraced property.