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Rad Size Calc? Correct?

Discussion in 'Plumbing and Central Heating' started by dishman, 17 Jan 2019.

  1. dishman

    dishman

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    I have used a few rad calculators for this room.

    Ideally I would want a single panel radiator.

    A while back I did the calculations and thought I needed a double. But, I had to put things on hold.

    Now I have come back to it, I have done a re-calculations and single panel does not look too bad..

    It is a 1930s semi detached property.

    The room is 3.96 (l) x 3.92 (w) by 2.5 (h) in metres.

    It has a double glazed upvc (circa late 90s) bay window with a glass area of 5.44m2. The bay is the only external wall.

    It has a heated bedroom above and a suspended timber floor over a void and soil subfloor.

    According to the various calculation websites, they comes up with a figure of 1400w.

    Does that sound correct?

    I was thinking of a long single panel of 1800 x 600 with convector fins which comes in at 1800w.

    Would this be too much or too little?

    Here is an actual room plan with dimension calculations.

    [​IMG]

    Much obliged....
     
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  3. dishman

    dishman

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    Just to clarify.....

    I would either get a 1800 x 600 double with single fins...

    Or just the single....

    But if the calculates indicate 1400w and a single of that size is 1800w, a double of 2500w may be overkill?

    Thoughts?
     
  4. RobTi

    RobTi

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    I think a condensing boiler still likes oversized radiators, but been a while since I was up to date
     
  5. dishman

    dishman

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    Yeh,

    But if the calcs recommend 1400w, and a normal oversize is recommended to be about 10% - which makes 1540w.

    Will a single panel at 1800w be more than enough....as that is about 30% more than the calcs suggest.

    Where as a double at 2500w (with single fins) is considerably oversized....I may just be going far too overboard.
     
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  7. John D v2.0

    John D v2.0

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    if you oversize all your radiators then that's good because you can run the whole system cooler thus saving a bit of gas.
    however if you just oversize one you still need the high water temperature for the rest of the rooms, so no more efficient but that room will heat up a lot quicker and the TRV will cut off more quickly.
    So yes if you plan to do the remaining radiators in future then go for it, but no point fitting one oversized rad on a system designed for high primary water temperatures on its own.
     
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  8. dishman

    dishman

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    Thanks

    It was less of an intentional oversize question.....more pure heat output required for the room.

    i.e Based on the room size/type and the numbers a calculator spit out..would a single be appropriate.

    Or, based on the experience of installers here, is 1800w not enough for a room of that size type.
     
    Last edited: 21 Jan 2019
  9. GoodDIYjob

    GoodDIYjob

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    I am not a heating engineer or installer.

    I have a 1930s semi. Internal, one large window area, one external wall area, v. similar sized to yours. I have a 1800mm x 600mm single panel / single convector in the room. It is adequate especially at higher boiler temps. Lower boiler temps and freezing cold it is ... well, just enough. The rad is on the wall opposite the window dbl glazed area (which are probably 15 years old) and it does feel cold nearer the windows, especially if the curtains are open.

    So in answer to your question, it will be adequate - just. If you want to run lower boiler temps a double panel maybe a better bet. The issue for me is that all the rads are already single, so if I upssize that one, that room will heat quickly but rest of house cold. Also, every 30mm of wall space counts!

    Another factor to consider is the whole of house heat output vs heat loss. So if the rest of your house is comfortably oversized, heat will move from other downstairs areas, and that would also help with running only the single panel......

    You make your choices,....
     
  10. ericmark

    ericmark

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    I made a mistake, an open plan house, never realised how much heat would go upstairs, so down stairs radiators had to be well over size, I tried adjusting the lock shield valves, but leaving a bedroom door open or closed would alter what was required.

    However things have moved on, the TRV and modulating boilers mean it does not really matter if a boiler is over sized, the TRV will compensate, what is more to point is minimum output of boiler.

    If the minimum output is 6 kW then unless the radiators switched on with the TRV's are over 6 kW then the boiler will cycle instead of modulating.

    So today radiators can't really be too big, the boiler can be too big, but not radiators, the lock shield valve and TRV will allow large radiators to be used without a problem.

    So the larger the radiator the faster that room can heat up, assuming the boiler has enough output, where this changes is with fan assisted radiators, as if they get too cool the fan will auto switch off, and fan assisted don't use the lock shield valve in the same way, but unless fitting something like the ivector then no problem going over size.
     
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  11. DIYnot Local

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