Current opinion about Vaillant EcoTec Plus 428?

[Dan Robinson]

See you in the CC

 

[simond]

Is there a Vaillant opentherm adaptor, Dan? Didn't think they supported Opentherm?

 

[Dan Robinson]

Details in the CC. There's a thread with my name written all over it

 

[D_Hailsham]

Update: I just received the installers reasoning (now that he's back from holiday):
"The gas boiler we have chosen for this quote is a Vaillant Ecotec plus 428, the reason for this is because of any extra radiators or underfloor heating to be added to the house ... .

The installer is making the mistake of assuming that the current radiators have been correctly sized and no changes have been made to the house since they were installed, e.g. double glazing, insulation etc.

The heat loss from a house is a calculable quantity determined by the size of house and construction - it doesn't change just because you install extra rads or underfloor heating - so the best way to size the boiler is to use the
Baxi Whole House Boiler Size Calculator. (This uses the Building Research Establishment methodology, so it is a "manufacturer neutral" calculator.)

It doesn't matter if the radiators and u/f heating add up to more than the calculated boiler size: in fact it's a good thing as the system will automatically run at a lower temperature, which is more efficient. Problems will arise if the rads are too small for the heat loss

As for the HW, the calculator includes an extra 2kW, which may seem insufficient if you have a 20kW coil in the cylinder. But don't forget that the boiler will only be running at full output for heating during the coldest days in the winter. Most of the year it will be running at less than half output. There is therefore a lot of spare capacity for producing HW. Setting the HW timer so the cylinder is heated when the CH is off also helps.

PS I assume you are not enlarging the house.

 

[Marmottefarcie]

Update: I just received the installers reasoning (now that he's back from holiday):
"The gas boiler we have chosen for this quote is a Vaillant Ecotec plus 428, the reason for this is because of any extra radiators or underfloor heating to be added to the house ... .

The installer is making the mistake of assuming that the current radiators have been correctly sized and no changes have been made to the house since they were installed, e.g. double glazing, insulation etc.

The heat loss from a house is a calculable quantity determined by the size of house and construction - it doesn't change just because you install extra rads or underfloor heating - so the best way to size the boiler is to use the
Baxi Whole House Boiler Size Calculator. (This uses the Building Research Establishment methodology, so it is a "manufacturer neutral" calculator.)

It doesn't matter if the radiators and u/f heating add up to more than the calculated boiler size: in fact it's a good thing as the system will automatically run at a lower temperature, which is more efficient. Problems will arise if the rads are too small for the heat loss

As for the HW, the calculator includes an extra 2kW, which may seem insufficient if you have a 20kW coil in the cylinder. But don't forget that the boiler will only be running at full output for heating during the coldest days in the winter. Most of the year it will be running at less than half output. There is therefore a lot of spare capacity for producing HW. Setting the HW timer so the cylinder is heated when the CH is off also helps.

PS I assume you are not enlarging the house.

Many thanks D Hailsham for the tip about the Boiler size calculator.
You are correct - we are not enlarging the house.
When I put our figures into the calculator it gives us a required figure of 20kW.
Thanks also to all the other contributors on this thread.
From ScottishGasMan's input it would seem that we should go for a 6 series system boiler either the 618 or 624 depending on whether we try to match the output of the old boiler (17kW) which has done us well for 20+ years or whether we go with the slightly more conservative estimate generated by this boiler calculator.

 

[St0rmer66]

I agree on the 6 series. 624 "at most", 618 should be fine though. A 624 can turn itself down a lot lower than a 428, so over-sizing is less of an issue with it.