Diasdvantage of bigger boiler

Maddie

Apologies in advance for the long post...

We are about to install a new combi boiler and new central heating system are are trying to decide which boiler to go for.

The house is a 3 bed detached with secondary glazing on most windows (not double glazed) and a solid wall (no cavity or insulation). We will have 8 radiators in total.

However, we are hoping in the medium term to build an extension which would bring us to 4/5 bedrooms and increase the house size by almost 50%.

We have been quoted for the Vailliant 831 with this is mind. However I am concerned that we will end up wishing we had a slightly bigger boiler as I don't want to be worrying too much about using taps when someones having a shower etc.

Therefore I asked for a quote for the 837 which has come out about £200 more.

My question is - what is the disadvantage in going for the bigger one other than the upfront cost? Is it likely to be significantly less efficient etc?

Any advise would be appreciated!

UncleZen

You may get a more informed response on the DIY board.

Maddie

Cheers, will ask there also

macman

Combis are sized on the flow rate, not on the CH output. When producing hot water, the flow to the CH circuit is interrupted.

Maddie

So what does that mean macman?

macman

Basically what I said. But if you install a combi, then you will not be able to run a shower and a bath, or two showers, at once, regardlesss of the flow rate.

Maddie

Ok, so if we ever put in another shower we'd need to make it an electric one. From what I'm hearing there want much point on going for the larger one.

macman

I suggest you start by comparing the flow rates on the 2 models.
What does your RGI advise, assuming you have informed him of your future plans?

Pincher

This has a "Here is 15 litre of hot water I made earlier" tank:

http://www.plumbnation.co.uk/site/vaillant-ecotec-plus-937-power-store-combi-boiler--flue---vrt-392-programmer/

It's a Vailant, too.

This is a halfway house between a combi and a traditional separate boiler and cylinder.

http://www.plumbnation.co.uk/site/natural-gas-storage-boilers/

The flue run can be tricky.

bengasman

macman wrote: »

But if you install a combi, then you will not be able to run a shower and a bath, or two showers, at once, regardlesss of the flow rate.

Total nonsense; large combis are perfectly capable of running two showers at the same time, or bath and shower as long as you don't run the bath at full whack.

No disadvantage to installing a bigger boiler other than extra cost.

C_Mababejive

You need to consider carefully your hot water requirements for your large family home. I would suggest that you consider having a high efficiency system boiler installed and a hot water storage vessel rather than having a combi fitted.There is nothing worse than not having enough hot water and dribbling showers that run hot and cold.