Radiator Size?

Discussion in 'Plumbers' Talk' started by RMH, Jan 7, 2007.

  1. RMH

    RMH New Member

    We want to fit new radiators in our victorian terrace. the existing units are single panel, very long and useless! The previous owners installed a Baxi 105E combi boiler which I presume is big enough for the job (3 x Bedroom) My question is: when using the on line BTU calculators I always get different answers depending on the web site, so far for one bedroom 2330-5360. Would it be ok to go for the maximum BTU suggested and then just turn it down if things get to hot?
  2. multi trade

    multi trade New Member

    Fit TRVs set them properly, they will turn down automatically.
  3. RMH

    RMH New Member

    Is it best to go for the higher rated rads? I would hate to have it all done only to find the system not hot enough!
  4. plummit

    plummit New Member

    Over sizing rads isnt a problem, apart from cost, and the visual aspect, on the whole. Obviously this is dependant on the system that you have.
    TRV's are a plumbers dream, over size and control via the trv.
    You see people will never complain about being to hot.
    I spent many a day sizing rads or convectors, when trv's were not about.
  5. RMH

    RMH New Member

    Hi Plummit

    Many thanks for that, thing is at the moment all rads are single panel and really ugly, so I will use double panel convection type so should be shorter anyway.
  6. it better to use single panels where possible because they spread the heat more evenly.

    Oversexed rads allow a lower flow temperature and greater condensing efficiency.

  7. RMH

    RMH New Member

    Hi Tony

    "Oversexed rads allow a lower flow temperature and greater condensing efficiency."

    Sorry to sound thick but what does that mean?
    BTW my combi isnt a condensing type
  8. tgs

    tgs New Member

    Sorry to sound thick but what does that mean?

    Radiator outputs depend upon the difference in temperature between the radiator (flow temperature) and room temperature. traditionally this was assumed to be 60C. The output or flow temperature of a boiler was about 86C.

    With condensing boilers, they work at greatest efficiency at a much lower flow temperature of 55C. This is probably too low for any radiator system to work so you have to compromise. The compromise is a flow temperature of 75C and a smaller temperature difference of 50C.

    If you over rate the radiators then you can drop the thermostat back a bit and the boiler will spend more of its time in condensing mode. Even on a normal boiler dropping the thermostat a bit reduces fuel bills.

    The best way to achieve a bigger reduction in flow temperature is to have more radiators but smaller. So instead of just one big one you have two (or three) smaller ones. The sum of these adding up to more than the big one. What this does is couple the thermal energy in the radiators into the room more effectively and allows better comfort at a lower room temperature.

    The downside, of course, is more cost, more piping, could be difficult to balance and more wall space taken up with radiators. Since in most houses wall space is often at a premium this option is not often used.
  9. RMH

    RMH New Member

    Hi tqs

    Thanks, that makes things a bit clearer. As you say its difficult to site multiple radiators in a room so I guess there is always a compromise.

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