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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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    We're just starting a self build project consisting of a detached property with ground floor and two upper floors.

    For heating we have been advised to install underfloor heating on all floors. With the current insulation regulations we're slightly worried of the possibility of damp issues should the property not have sufficient ventilation.

    The question is should we be installing an MVHR system on top of the underfloor heating. ?? Or will trickle vents on the windows be enough to provide ventilation??

    I feel if we have both installed one or the other may be seldom used.
    • CommentAuthortony
    • CommentTimeAug 17th 2014
    You should be deciding your own U-values and better ones than the minimum acceptable

    I would want an airtight house and MVHR, if you have good U-values you wont need heating, possibly on the g/f only if bad U values.

    Window vents are uncontrolled and virtually uncontrollable ventilation, too much when windy, none when it is calm.

    You want MVHR
    • CommentTimeAug 17th 2014 edited
    Heat load and MVHR should be consider separately.

    Heat load is the sum of fabric losses and air losses
    MVHR efficiency is is the integral of just air losses.

    So it is possible to have a poorly insulated house but with good airtightness or a house this good insulation but poor airtightness. Or anywhere in between.

    Get your detailed design sorted, work out the losses and then decide the best system to use. Hard work trying to decide the other way around.
    Unless you want both, but as cheap as possible to run, then that will lead you to a very well insulated 'box' with very low ventilation losses.
    I'm at a bit of a loss with your answers guys......sorry.

    Are you saying spend money on insulation and sealing the house properly and have MVHR system in place ?? With UFH installed on the ground floor only just in case ?
    • CommentAuthortony
    • CommentTimeAug 17th 2014 edited
    Yes, you might consider UFH in bathrooms and/or heated towel radiators
    MVHR and heating system are, in effect, unrelated.

    Even with moderate air tightness (such as my retro fit scenario) MVHR is very valuable even if it doesn't necessarily have a payback (return on investment) in terms of saved heating energy paying for the capital outlay as would be the case in a really airtight house.

    UFH is the best choice for heating if possible.

    If you target minimum regulatory insulation values you're probably on the wrong Forum but that doesn't mean to say the high levels of insulation and build quality required for a zero heating house will be right for you either however with a 'self build' that should at least be your starting point.
    • CommentAuthoralec
    • CommentTimeAug 18th 2014
    UFH is only a good choice if the controls vary the boiler and flow temperature in tandem..its pointless to run a boiler at a fixed temperature when the heating load varies...especially as low loads can be achieved at very high efficiencies ...
    You cannot really make any judgments about how much heating you need, and where, until you know what fabric U values - and thermal bridges - and level of air-tightness your house is going to have. What others have said is right though, that you may need UFH on the GF only, or even less than that, if you go for a very well-insulated and well-detailed 'tight' house. If you let us know your targets (fabric U values, and air-tightness in m3/m2/h or air-changes/hr - ACH) you'll get some more targeted advice.

    Lots of scope for really good results. Enjoy it!

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