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Discuss Are oil boilers suitable for smaller properties - eg an annexe? in the Oil and Solid Fuel Forum area at

  1. DevsAd

    DevsAd Member

    Hello all.

    We will likely have to move soon so we can find a new home which has room to have a separate annexe built for mum in law. As it'll be out in the sticks, the fuel supply will most likely be oil.

    A few questions on this, please:

    1) Do they make small oil boilers - ideally combi types - suitable for a small, 2-bed, single-storey home, likely size around 12m x 6m? If so, any recommendations? Do oil combis work well enough - eg how quickly do they fire up on demand? Do they pre-heat?

    2) Are oil boilers suited to UFH? Is UFH easy to zone and control for individual rooms - living area, bathroom, 2 beds?

    Many thanks.
  2. Best

    Best Trusted Plumber Top Contributor!!

    Never installed one, but you can get oil boilers that have a small output.
    Grant boilers are from 12kw for wall hung or from 15kw for their floor standing Vortex range. Still going to be plenty output above what you need, but that won’t be a problem. The proper controls will ensure the boiler doesn’t cycle on and off.
    Oil combis can have a heat store as part of them and therefore instant hot water to taps. Personally I hate oil combis and prefer a heat only oil boiler and a hot water cylinder - vented or better still, unvented cylinder.
    If suitable, consider an outdoor module.
    Last edited: Jul 3, 2018
  3. DevsAd

    DevsAd Member

    Thank you Best.

    Are there any reasons to hate oil combis more than gas ones?

    I know that combis in general are a compromise when it comes to hot flow, but for such a small house I'd have thought it ideal? Or is it to do with oil-fired combis?

    If 15kW is the max combi output, that would relate to a poor hot flow of, I dunno, around 7lpm or so? In which case I'd agree - that's poor!

    An external home for the boiler is a good call, tho', and presumably a pressurised hot tank could be installed in there too? (One of the reasons for considering a combi was for space.)

    I'll have a gander at these Grant boilers you mention.

  4. Best

    Best Trusted Plumber Top Contributor!!

    I hate oil combi boilers because they are very complex and give a lot of bother. They are also very expensive. (You can buy a good heat only boiler plus an unvented hot cylinder for less than a combi!)
    I dislike them so much I prefer not to service or repair any.
    Your hot water flow rates for a small home with only one or two people will be fine though with a combi.
  5. DevsAd

    DevsAd Member

    Thanks again, Best.

    Yes, I've just seen how much they cost! And if their reliability record is worse even than gas combis, then that's a point really worth considering.

    Cheers - really appreciate the info.
    • Like Like x 1

    MARTIN LISTER Pembrokeshire Gas Maintenance GSR

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