Great calculations, all of this is explained in the book written by Lewis named " an introduction to low temperature design" .

Thanks great video, after doing the calcs, 6 of my 13 rads will need up sizing to overcome heat losses at dt30, plus of course a larger expansion vessel due to the systems increased water volume, all good to know now rather than the hidden costs later when I get round to having a new system boiler installed.

Allen, just seen this ! Fantastic video! Keep up the good work!

Thanks for the video and trying to help guys out, the problem I see with a lot of this is I see jobs everyday that have been thrown in not flushed out sometimes incorrect gas pipe size and no controls until we can get rid of these types of installers and it’s policed properly what’s the point because some numpty will just come along chuck a boiler in and leave and nobody takes them to task

Awesome efforts thanks to you all 😊😊

Does that conversion factor of 1.3 work for any flow temperature. I’m sizing rads for my own house and I’d like my rads to work on as low as a 38° flow temp. Thanks lads great bit of information

Is this a move (slowly) towards regulating boilers off the market, making way for the heat pump they seem so keen on premoting

Thanks allan an micheal your videos are a credit to yoursleves, as a gas engineer who doesn’t do much install i find these fascinating, silly question but would Over sizing a radiator help heat the room quicker and stop the boiler working harder?

So am I right in saying if I go to quote a combi for combi install I now have to do a room size calculation for each radiator so that they can run on a 55 degree flow temperature?

I have a viessmann combi with their weather sensor, I've set the boiler to 20'c I leave the boiler to do the rest.

The Official testing of Radiators heat output is in a purpose built test Lab with Top Bottom Opposite Ends (TBOE) heating flow and return pipework connections. This is the most thermal efficient of internal cross flow waterway distribution passing through a Heating Radiator However, The most common Radiator connections in a domestic home is Bottom Bottom Opposite Ends flow and return pipework connections. Therefore with BBOE connections further adjustment of calculations will be required. To obtain the full output of heating radiators mounted on external walls, it is essential that foil thermal insulation is installed behind the radiators. By taking this action you are preventing more building fabric heat loss passing through the external wall from the Radiator. The thermal insulation ensures that heat emitter is heating the rooms air rather than wasting it through an external wall. The majority of heating radiators in homes are normally positioned on external walls. So you can make a low cost improvements to obtain long term saving to your annual running costs. Modulating Gas Boiler controls such as Automatic Weather Compensators are an essential energy saving investment. The ensure that the additional use of outside temperature detector is used to regulate not only the combi boilers heating flow temperature but also automatically reduces down / modulates the gas boilers burner (ratio's 6;1 of load/demand) Please remember that your boiler and radiators design outputs are for when the external outside temperatures are minus 3.C to give you an internal temperature of 21.C in the living room for example. So with this arrangement your full demand loding is a 24.C increase. However we all know that for the majority of the year outside temperatures are a lot higher on a annual average. Enter the Weather Compensator this measures the external and internal temperatures and automatically adjusts (modulates) both the boiler/ burner and the heating flow temperatures to take into account the 'changing and actual all year round weather conditions'. Just say for example the outside temperature is 10.C the WC control work out and calculates just how much energy is required to reach your internal set point temperature of 21.C in the living room. The WC controls can still be used even if you reduce your heating systems maximum flow temperatures from 75.C mean to a lower 40.C mean It's just a case of changing the WC controls air temperature and water temperature: The Ratio's

What this boils down to is multiplying your heat loss calculation by 2.5 when picking a dt50 radiator to run at dt25. Not an insignificant increase.

Hi Alan, great video with you and Michael. I think you may have missed an important point here. The customer is going to feel colder, because the actual energy emitted is lower. The loss factor Michael has used also indicates how much more heat won't be emitted to the room. Using Michaels numbers for the customer to feel the same heat effect do we not need to use a radiator with twice the emmittwd power? I

What radiator flow rates are required to give a td of 5c. Most installed pipe work won’t be able to give a flow rate capable of 5C

Great video mate. Struggling to find that app. Any idea on how to find it or got a link?

Based on his calculations, yes the rad running at dt25 will be enough to overcome heat loss at 20oC but how long would the room take to get to 20oC if the setback temp is say 17.5oC? I suppose that’s where Open therm comes in.

Heat pump At 50c! , you need to rethink that one.

What if the copper going into that radiator is 9 or 10mm microbore? Is the radiator still suitable at 55?

How are you finding out the return temperatures from a boiler to a air, or even a hybrid system? Surely each system be slightly different on the return temps depending on heat losses? And would a boiler not need to be set at 65 to kill Legionnaires in the hot-water and will there be less water storage on a lower temperature? Great video 👌🏻

Sorry one more thing too, the ammount of time this is going to take to get the heat that want must take much longer so the boiler will still probably use the same or more gas to achive the objective.

My central heating is low temperature, I can't afford to put it on.

Hi. Great vid. Thanks. My maths is a bit dodgy. How do you get 0.5 to the power of 1.3 to be 0.406. What buttons do you push?? )) Thanks

Great, but how do you estimate what your room heat loss is?

What if the copper to that radiator is only 10mm. Is the radiator still suitable?

I think we're missing the point of where this excess heat from the over-sizing of radiators in years gone by, goes. Manufacturer's data is good for a new clean radiator. But has the years run by, the available output from these radiators lessens as the internal state of the radiator conducting surfaces degrade. The excess ouitput capacity of the radiator would therefore compensate for this. Lets assume a mere 25% degradation (it's probably more) of catalogue output for the radiator in the given example. Were now only getting about a max output of 923W from the radiator, which is obviously a shortfall. The output of the radiator at lower flow/return temperature being about a maximum 375W which will obviously result in cold unhappy customers?

On a combi boiler with no digital display, what will be 55°.?

whats the coldest it gets over there? Im in Canada , our coldest days of the year range from -35 to -50. a 55 flow temp works on my system up to about an outdoor temp of -15ish. ... at -20 outside , it struggles . 58 degrees flow temp works. past -30 it seems a 60 degrees+ flow temp is required...

If a radiator receives water at 60 -65 degrees and it takes 4 hours to raise the room temperature by 4 degrees how much longer will it take to achieve the same result at the much lower mean water temperature now being promoted. ?

When your caption said combi boiler only did you mean condensing boiler only

If your heat loss for the room is 500 Watts the why would you have a radiator that emits 1231 watts?

I’m afraid your calculations seem incorrect. The calculation is only to maintain the temperature based on 500w heat loss. You must still heat the room first which needs much more heat to get up to temperature. Once at desire temp I agree.

We did a video on this point for customers as it’s a big subject to get across to them. Check it out. kzfaq.info/get/bejne/pc2peq2jldmYqWQ.html

I'm sorry but I must be the thicky in class, how on earth is this rad going to heat the room sufficiently with a heat loss of 0.5 kw surely you would need at least 0.5kw and more to get the heat up, I'm probably doom and gloom but I cant see my customer putting up with luke warm rads and it is only going to me they keep calling when granny is shivering in the corner

And your telling me, installers will actually do this going forward? Boxt? BG?

I could get in my car and drive from Leeds to London at 20 MPH,would I be happy,I think not. I could set my boiler to 52 Deg come home, turn the heating on ,and wait 8 hours for the house to warm up,would I be happy,I think not. C’mon Allen tell the subscribers the truth this is another load of rubbish.