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Green Building Bible, Fourth Edition
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Heating and cooling: Radiator bottom temperatures

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  1.  
    • CommentAuthorEd Davies
    • CommentTimeApr 26th 2021
     
    Just had a plumber round to service the oil boiler here (rented house).

    I mentioned that the bottom middles of quite a lot of the radiators in the house, particularly downstairs, are cold even when the heating has been on for a while presumably because they're sludged up. Nope, he said, that's how it should be. Am I right to be sceptical? I think they should be a bit cooler than the top, of course, but not stone cold.
    • CommentAuthorSimonD
    • CommentTimeApr 26th 2021
     
    No they shouldn't be stone cold. Sounds like the system needs a good clean and flush.
    •  
      CommentAuthorfostertom
    • CommentTimeApr 26th 2021
     
    Shd be negligible. Rad output calcs assume no difference.
    • CommentAuthorEd Davies
    • CommentTimeApr 26th 2021
     
    Thanks for the confirmation chaps.
    • CommentAuthorowlman
    • CommentTimeApr 26th 2021
     
    What type of rads are they, e.g. modern column ?
    • CommentAuthorEd Davies
    • CommentTimeApr 26th 2021 edited
     
    Just ordinary, mostly double, radiators with fins between. Installed a bit over 20 years ago, I assume. Here's the one in the kitchen with temperatures (°C) taken from an IR thermometer with spurious precision as the numbers were wandering around a bit, I assume due to reflections, etc.

    For comparison the similar, but a bit shorter, radiator upstairs in the little room I use as my study had a centre-top temperature of 54°C and a centre-bottom temperature of 48°C which is much more like what I'd expect.
      img_3256.jpg
    • CommentAuthorowlman
    • CommentTimeApr 26th 2021
     
    The reason I asked Ed, was that modern column types are "handed" i.e. flow/return ends, and as such frequently have a baffle inside the flow entry which directs the incoming water to the top before it continues its path down the columns to the opposite end. These types can often benefit from system re-balancing using the lockshield.

    However in your case as others have said, sludge seems to be the obvious cause, but strange your plumber thinks otherwise. You could drain one yourself as a trial, and take it into the garden and stuff a hosepipe in and see how much sh** comes out.
    If that looks like the culprit either do the lot individually yourself, or get a full plumbing flush via the landlord.
  8.  
    The problem could also be a balancing issue or too low a flow rate on the pump. Is there any difference if you up the speed on the pump ? - if it's not already on full.

    As far as I can remember radiator output is calculated with a 10 deg drop between input and output.
    • CommentAuthorphiledge
    • CommentTimeApr 26th 2021
     
    Looking at the temperatures with little difference between the sides, it looks like youve got a good flow up the sides and across the top. As suggested, Id be tempted to shut off both valves(make a note of the turns on the lockshield), drain the rad and wash it out with a hose.
    • CommentAuthorEd Davies
    • CommentTimeApr 27th 2021
     
    Posted By: Peter_in_HungaryIs there any difference if you up the speed on the pump ? - if it's not already on full.
    Unfortunately, it's already on full.

    With the summer coming and me probably only being here for one more winter I'll leave it to my landlord to decide what to do but this thread has been really helpful for me to stand my ground that there is a problem.
    • CommentAuthorDavidND
    • CommentTimeJul 2nd 2021 edited
     
    <blockquote><cite>Posted By: Peter_in_Hungary</cite>The problem could also be a balancing issue or too low a flow rate on the pump. Is there any difference if you up the speed on the pump ? - if it's not already on full.

    As far as I can remember radiator output is calculated with a 10 deg drop between input and output.</blockquote>

    Prize goes to Peter :bigsmile:

    I'm not a betting man but I'd put 50p on it being a combination of both balancing & sludge. See it every single day. BTW the pump is rarely set to speed 3. If it is in a normal semi then it's an indication of other issues.

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