Vaillant or Worcester Bosch Heat only Boiler?

[rogerse]

I have just decided to have a Megaflow 210ltr cylinder installed and a complete refit for my house, which is a 3 bed semi, soon to be 4 bed and 2 bathroom, due to loft conversion. What boiler should I buy? I have been told to go for either Vaillant or Worcester Bosch. And which model too? I think the size of house dictates around 80,000Btu. One source of advice is telling me to get the size right so that the boiler is working at or near capacity, while another says get one that will easily do it and therefore wont be strained.

Any thoughts?

 

[Slugbabydotcom]

One source of advice is telling me to get the size right so that the boiler is working at or near capacity,

The boiler does work more efficiently if this is the case. Don't forget to allow for any future plans of building an extension though.

As for make of boiler well you pays your money and takes your chance. Put more emphasis on getting whatever boiler properly installed on a properly flushed system

 

[ChrisR]

Add up the potential outputs from the rads (compare on a chart) and see how much is left for heating the cylinder. A Megaflo can absorb 25kW = 85.000Btu/Hr all by itself.

 

[Slugbabydotcom]

A Megaflo can absorb 25kW = 85.000Btu/Hr all by itself.

Thats 24.5 kw and for the largest 300 litre megaflow
The one that would fill a bath [125 litre and have enough left for the pots could recover in 15 minutes with an input of 18.3kw

My message is don't put too much emphasis on the hot water side unless you use lots of it and need the fast recovery times. All but the largest electrically heated megaflows get by with a 3kw immersion and I would say this is more than sufficient to add on to your heating requirements. It can have more output from the boiler when it is not providing heating.

Theres a calculator here to help size your boiler. Here they only allow 2kw for the hot water load

 

[Agile]

You would have a very large house if you needed 22 kW of heating.

I fitted a 24 kW to a large six bedroom detached house with poor loft insulation and a 300 litre cylinder and the boiler is cycling for only about 35% of the time during normal winter weather. When the outside temperature is -5°C it might be on most of the time.

Its far more efficient to have a smaller boiler and one way to ensure there is no conflict on the heat output is to start water heating an hour before the heating is required in the mornings.

The 15 kW absorption of a 300 litre cylinder has to be taken with a few pinches of salt. It will be much less if the boiler flow temp is only 65°C and is likely to reduce further as the water in the cylinder warms up.

Tony