Oversize Boiler, renew now or later?

[Bearnie]

We desperately need a new oil fired CH Boiler, the present one is 17yrs old and very tired. The problem is that in 2 years time we are planning an extension to the house, a downstairs living room and an extra bedroom and bathroom above. I'd do it now but can't afford to just yet. Even if our old boiler lasted that long it wouldn't have the output required so a new one is on the cards.
I've been given conflicting advice about this, some say 'fit the new boiler now, it won't be a problem' while others say that, 'a boiler that's too big would be inefficient and could suffer damage'. Needless to say, I'm confused and would like some more input on the subject. Your thoughts would be greatly appreciated.

 

[sturharv]

I cannot see this being an issue. If you try and select a model that can operate between a minimum and maximum kW output (as most oil boilers do) then you will have scope to increase the boiler demand i.e. after the extension, it will be happy running at its minimum output.

Boilers tend to be 'oversized' slightly anyway.

 

[Agile]

Boilers tend to be 'oversized' slightly anyway.

Not when the are correctly sized according to the rated heat loss of the property!

In spite of the energy efficiency courses installers have to go on I have seen many boilers fitted which are more than twice the power needed. That makes the overall efficiency very poor.

Are there any modulating oil boilers on the market?

Tony

 

[Nixt]

No there are no modulating domestic ones, burners are single stage. They can be range rated so you can oversize model and up the output as mentioned earlier (most oil combi's are oversized for CH), undersizing is the problem as it leads to poor return temperatures and water jacket corrosion.

 

[htgeng]

No there are no modulating domestic ones, burners are single stage. They can be range rated so you can oversize model and up the output as mentioned earlier (most oil combi's are oversized for CH), undersizing is the problem as it leads to poor return temperatures and water jacket corrosion.

Viessmann do a very nice wall mounted oil boiler. Unfortunately its not available in the UK market! They must be missing a trick I think considering the millions they are spending on promoting the gas side! Even my local rep was frustrated by 'Germany' on this issue.

 

[sturharv]

Boilers tend to be 'oversized' slightly anyway.

Not when the are correctly sized according to the rated heat loss of the property!

Yes I agree, it is always better to try and size the boiler as accurately as possible based on the anticipated heat loss, 'u' values, building fabric, internal / external temps etc. but they do tend to be oversized 10% or so for safety... even on oil boilers, I think most installers would agree with that.

Gas not so much of a problem, still try and get as close as possible, but they do modulate.