Got an old boiler trundling along in the airing cupboard at home? are the big freeze's sub-zero temperatures making early morning starts unbearable? Your flow rate multiplied by . gives you a rough idea of how powerful a boiler you’ll need in kilowatts, assuming your cold water comes in at about c your installer will be able to check your temperature and flow rate and help you make an accurate assessment. Check back often as more comfort solutions are coming soon! Hardly music to my ears the salesman.