Natwerk Designs

How do you work out the size of boiler to get, as no real info on working out capacity for baths kitchens etc?

The boiler would need to service kitchen, loo, utitliy with sink, & bathroom with seperate shower - shower we want to be run straight from boiler (yes we know we need a scold preventing thingy) we are also planning on doing extension approximatly 5m by 4m but this we want to be done by underfloor heating The btu for this room will need to be 8821 (lots of glazing) for the rest of the house, it needs to be approximatly 4100, (we have oversized some of the radiators, due to getting it from a combined central heating pack and so we get the look rather than the right btu, but none are too small for the room!) It is a toss up between these worcester condensing combi boilers 40CDI - 40kw - 136,000btu - 16.0l/min 35CDI - 35kw - 120,000btu - 14.3l/min 30CDi - 30kw - 102,300btu - 12.7l/min 30SI - 30kw - 105,000btu - 12.3l/min we chose worcester as it got the least amount of critisism from this site, could someone also explain the difference between CDI and SI in the worcester boiler

Public Comments

1. The size of boiler depends on various factors, like the type of building, the size of building, size and how many windows, insulation etc. Your best bet would be to find someone with a mears calculator or a web site somewhere. Whatever way you would have to get the tape measure out.
2. Don't bother with the companies selling the worcester/bosch boiler - find one selling a vokera - normally an independant with intelligent staff who will be pleased to help you. Take your measurements to them and they will usually be pleased and ABLE to correctly spec. your requirements. The independants care - the others have a job. The vokera range are excellent, efficient and very affordable. Just as an afterthought - if the extension is heavily glazed - like a conservatory - can i suggest that you use electric underfloor heating and then use a heat exchanger type of air con. unit - wall mounted if possible which will then give you optimum temperatures in both the summer and winter. We have a Hyundai air con/heat pump fitted in our conservatory for 6 years and it gives us a room we can use for 12 months. Have it mounted a minimum of 6 feet above the floor on a brick wall - the 'mother unit' and connecting pipework can be located up to 30metres away outside. We can have a room cooler than our fridges in the summer and combined with the electric underfloor heating which is switchd on from November to April we can wander around in 80+ degrees in the winter time in short sleeves. Mounting at this height stabilises temperatures. In the summer time the blast of cold air from the unit is pressed down by the warm air from above and cools the room and also helps to stop the sun from damaging your furniture - in the winter the heat from the unit is pressed down by the cold air from above which has the same effect thereby giving you the best of all worlds. However they are not inexpensive to use but not really a luxury. Central heating in a conservatory is wasteful and totally inefficient.
3. For all your requirements, I would go for the 40 CDI. The letters refering to the boilers are just the manufacturers code fro different models like you have with cars
4. Go to your local plumbing centre and they will happily sort you out...