Boiler upgrade requirements for extension

[JimExtension]

Hello, we are planning a rear extension which will add an new UFH system, one extra radiator, and an extra towel rail.

Currently we have a 10 year old Worcester Bosch 25si combi boiler which is doing alright. It has recently been serviced and the gas engineer said it is looking good.

Obviously they’ll be some new load on it with the extension.
Is it acceptable to keep the existing boiler and see how it does, then decide whether to upgrade later?
Or are their any energy efficiency rules in place that would mandate that we replace it with a newer model?

Thank you!

 

[oldbuffer]

1. Keep it and see if it has sufficient capacity. Change later if needed.
2. You can get a rough and ready feel for it:
2.1 Allow 2 kW for every large radiator (including new one if appropriate).
2.2 Allow 1.5 kW for every medium radiator (including new one if appropriate).
2.3 Allow 1 kW for every small radiator (including new one if appropriate).
2.4 Allow 100 watts per square meter for UFH in concrete, 75 if under suspended floor.
2.5 Sum the above to get a rough heat requirement.
2.6 Add 10% allowance for it to heat up from cold.
2.7 If the result is 25Kw or less you should be OK, but no guarantees!
3. Be careful that pipes are sized correctly for the additional load. I wouldn't be happy if the extension is fed via 15mm pipework from the existing system. I'd want to see calculations that proved that was sufficient.
4. There are no energy efficiency rules mandating a new boiler for an extension However:
4.1 The situation is different for conservatories.
4.2 There are rules which will apply if you have to replace the boiler. Mostly to do with controls, generally not hideously expensive to comply.

 

[JimExtension]

Thank you so much. That is really helpful

 

[flameport]

Unless your house is vast you don't need a new boiler.
Combi boilers are sized for hot water delivery and are almost always grossly oversized for heating.