what size boiler should i be looking at?

[SafeGasInstall]

Flow restriction valves to kitchen sink , washhand basin will help you keep the flow to showers

 

[jimbob123]

thanks a lot for all your replies. you have all been very informative. so now im looking for a boiler that gives up to 14.8 l/m and that should be my combi selection sorted?

 

[Mike Jackson]

I'd try and get the flow rate up a bit first before deciding on a combi. IMHO 14.8l/min is too low. If someone turns on a cold tap the hot flow will drop too low and may represent a scalding risk. I always look for a minimum incoming flow rate of at least twice the hot requires. So for a 24Kw boiler, which gives a flow rate of 9 l/min I want 18 l/min. For a 38Kw boiler I'd be wanting to see about 30 l/min or more. No point in spending out on a high output combi if it won't work to it's full capacity.

As far as boiler goes look at the Atag 325C and325EC. Cracking boilers and really good value for money. They'll modulate down to around 6kw as well.

 

[GasmanxxxR1]

Whats the obsession with combis. I hate the things

 

[doitmyself]

I always look for a minimum incoming flow rate of at least twice the hot requires. So for a 24Kw boiler, which gives a flow rate of 9 l/min I want 18 l/min.

I don't see the logic in that. The 24kW boiler will raise the temperature of water flowing at 9 lpm by 35C, i.e. from 5C to 40C. This means you can run a shower/bath using hot water only. If you have an 18lpm flow you can only use the excess flow as cold water - washing car, flushing the toilet, cold fill washing machine. You can't use it for a second bath/shower.

 

[Mike Jackson]

That's exactly what the excess is for. Otherwise little Johnny is washing his hands under the hot tap in the kitchen sink. Dad has a slash in the downstairs loo and flushes it. As the stop tap is in the downstairs loo the cistern will draw cold water and reduce the flow to the boiler. The flow to the boiler reduces to 4 l/min and, briefly, before the boiler modulated down the water is heated to 80°C. Little Johhny ends up in A&E with full thickness burns to his hands.

You should be able to operate another outlet in the property without it reducing the flow through the boiler.