Combi boiler kw - conflicting quotes - advice

[hslondoner]

Hi,

I have a small 2 bed mid terraced cottage, one bathroom, 5 rads + bathroom towel rail.

Looking at putting in a combi boiler (currently no boiler in place - rennovating) and have had 3 different boiler models (and quotes) from different plumbers and now confused on which route to go down. Main concern is having enough kW for the property

Using http://www.idhee.org.uk/calculator.html to check kW required, being over generous with my values it suggests I need 18.8kW for the property size

These are the models that have been recommended:
WB Greenstar 30CDi 30kW
Valient ecoTEC plus 824 6.7 19.0kW
WB Greenstar 30Si 24kW

The kW vary quite a bit on these - the cheapest quote I have is for the Valient (and inclined to go with this as on a budget & includes 5yr gurantee), however my last property had a WB which gave no problems in the 4 years living there...

Just looking for advice and see what other people would go for in the same position - is a 19kW combi adequate for a small 2 bed house?

Thanks in advance!

 

[DeltaT2]

With a combi the Central Heating output is rarely an issue, but the Hot Water production IS!! For any property with a bath a 30KW combi should be the very minimum size fitted. Also; get your incoming mains water Dymanic Pressure & Flow rate checked at evening Tea Time(5-7pm).
HTH
Tricky Dickie Puller........

 

[hslondoner]

That's good to know... the house does have a bath (small 1500mm) and will have a mains run shower – which will primarily be used rather than a bath.

Might ask our Valient guy to explain his reasoning behind going for the 19kW (as he was a decent guy - ideally like to go with him).

Cheers!

 

[D_Hailsham]

Using http://www.idhee.org.uk/calculator.html to check kW required, being over generous with my values it suggests I need 18.8kW for the property size

Just looking for advice and see what other people would go for in the same position - is a 19kW combi adequate for a small 2 bed house?

Unless your 2-bed mid-terrace house has very large rooms and external walls made of cardboard, 18.8kW will be considerably more than you need to heat it; 8kW would be more like it.

But as DeltaT2 says, combi boilers have to be sized for the HW requirement, which depends on the incoming cold water flow rate. You need 2.5kW per litre/min to give a 35C temperature rise.

Make sure that the minimum CH output of the boiler is less than the heating requirement of the house.

 

[Agile]

Exactly, about 8 kW will be needed. It does serious harm to efficiency if you over rate a boiler.

All combis are a minimum of 24 kW for water heating. About 30 kW is better as it does not struggle in the winter.

Any decent installer should be able to fit any make of boiler. Some are drawn not by the client's best interests but by which model they get the best price on.

Tony