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Should I open the lever valve a bit to get more flow to my furthest rads?

Discussion in 'Plumbing and Central Heating' started by pedr0, 18 Mar 2021.

  1. D_Hailsham

    D_Hailsham

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    I should have said that your boiler does expect a flow/return differential of up to 20C. The higher the differential, the lower the flow so the smalller the pressure loss. In which case the bypass may not need adjusting. Correctly balancing for a higher differential should solve your problem.

    What procedure did you follow when balancing the system?

    What is the total kW (at 50dt) of your radiators?

    Do you know the actual heat loss of your house?
     
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  3. MJN

    MJN

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    Be very careful with this terminology. Whilst the term 'delta T' in the generic sense can refer to any difference in temperature values, in the heating world (and radiators in particular) it usually refers to the difference between the temperature of the room and the average temperature of the radiator.

    When referring to 'delta T' across a radiator I'd suggest using the term 'temperature drop' (or similar) to avoid confusion.
     
  4. D_Hailsham

    D_Hailsham

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    I was being very careful and was referring to the room/mean rad temperature difference when I asked:
    I was drawing attention to the fact that the radiator catalogue the OP referred to shows outputs at ΔT = 50C and ΔT = 60C. I was making sure he used the right one. Calculation of the output for smaller ΔTs (and different temperatures/drops) just requires the application of a mathematical formiula.
     
  5. MJN

    MJN

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    Understood, and it was the use of the same term to describe flow/return difference that has the potential to cause confusion hence me urging caution:
    It's no big deal though; I could just see the confusion creeping in.
     
  6. Harry Bloomfield

    Harry Bloomfield

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    Get a sheet of paper, plus pencil and mark the angle before you start - you can always go back to it then. I would start with wide open, just to see if it does in fact make any difference.
     
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  7. pedr0

    pedr0

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    Indeed - the first mention of deltaT did prompt me to search, and the results pointed to difference between average rad temp and room temp. Hence my post #9. But the maths revealed that definition of deltaT probably wasn't the one intended.

    I didn't do anything at the boiler. I opened all valves at the rads, then recorded the order in which the rads heated up. I turned the system off then closed all the rad valves. Then starting at the first rad to heat up, I opened the valve to get a 11 deg drop across rad (measured by putting black electrician's tape on the feed and return pipes and then pointing one of those IR thermometers at the black tape.). Then I moved onto the next rad and repeated until I got to the last ones to heat up.

    Not sure. I'll track down the original order and figure that out and report back (probably on the weekend now).

    No I don't. I was told by the original installer what heat output I'd need for each room. But I don't know how he calculated that. Contractor has gone bust so I have no way of contacting original installer.

    Thank you for all your help everyone. I need to get the figures of my rads and get back to you.
     
  8. MeldrewsMate

    MeldrewsMate

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    So if temp in = 70C and temp out = 60C your average rad temp would be (70-60)/2 = 5C ???
    A litttle more care with the maths methinks!
    Average = sum of components / number of components....I know, I'm just being pedantic.:sneaky:


    Correct.

    On the general point of balancing, all of your ball valves should be fully open. The restriction to flow is set individually on each radiator by its lockshield valve. There is an equivalent usually built into the UFH manifold (adjusted with a bleed key under the electric actuator).
    If the lockshield (LS) valve is fully open the flow through that rad is at its highest and the water has little time to lose temperature, therefore the out temp will be closest to the in temp, and the rads average temperature will be at its highest, giving out the most heat.
    CLOSING the LS will restrict the water flow, consequently it will dwell longer in the rad so the out temp will be lower, and it's average temp will be lower, and it'll give out (emit) less heat to the room.
    It has been suggested that you restrict the water flow though each rad until you get the out temp to be 20C lower than the in temp. That's all you need to do - but remember to do your adjustments with all TRVs fully open, and with all the UFH actuators removed. Usually you'll find one large rad needs its LS fully open, and most towel warmers need just about a quarter turn from closed to get that 20C drop.
    Above all, be patient....those cast iron rads are slow to warm, slow to cool.
     
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