How To Size Radiator’s For A Low Temperature Central Heating System

[@ian1104]

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

[@AllenHart999]

Great point

[@MrDougie1403]

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

[@HaroonAzhar-wx5ig]

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

[@alanwoods4023]

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

[@Chatterisdotbiz]

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.

[@andycarr9677]

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

[@squadmeta]

Original setup gives 1231watts. New setup gives 500watts. Even with another rad the same size still a shortfall of 231watts! Time to heat room drastically longer, customer unhappy if they heat room from a cooler start temperature. He did miss the point, you didn’t.

[@ianross5019]

At approximately 9 minutes you demonstrate that the existing radiator would match the heat loss of the room. Sounds great. But simple physics tells you that you now need to have that radiator “hot” permanently. The radiator output is effectively balanced to the heat losses of the room (Second law of thermodynamics here!). Previously the heat output of the radiator was 2.5 times the losses! So we will go from a system that, essentially only needs to actually run 30% of the time to a system that needs to run 100% of the time! Tell me how that is more efficient or how that saves energy? Bold statement at minute 20! Heat pump flow of 55degrees! Try that in North Yorkshire when it’s -5 outside!

[@heatpump8566]

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

[@ianross5019]

At approximately 9 minutes you demonstrate that the existing radiator would match the heat loss of the room. Sounds great. But simple physics tells you that you now need to have that radiator “hot” permanently. The radiator output is effectively balanced to the heat losses of the room (Second law of thermodynamics here!). Previously the heat output of the radiator was 2.5 times the losses! So we will go from a system that, essentially only needs to actually run 30% of the time to a system that needs to run 100% of the time! Tell me how that is more efficient or how that saves energy?

[@neo_265]

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.

[@handle1196]

Run it on weather compensation so its on longer periods at lower temperature?

[@nicholashughes5287]

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

[@joncoke8208]

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?

[@adobo6905]

The boiler generates heat (BTU), and radiators dissipate heat. Assuming your boiler is sized and selected properly, oversized radiators will deliver 100% of the total boiler-rated BTU capacity quicker than undersized radiators and will not harm the system or make the boiler work harder. Oversized radiators will cost more to buy and will take up more room.

[@reecehughes8932]

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?

[@samsavino17]

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.

[@bpercival2413]

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.

[@nt5366]

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?

[@danroseracing3512]

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 👌🏻

[@AllenHart999]

We are justing testing it at the moment. more videos to come.

[@dorsetengineering]

Hot water priority takes care of the higher temp requirement for legionella protection. Recent urban plumbers video covers this.

[@Bandits_At_3_o_Clock]

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

[@AllenHart999]

It should be yes. You can turn the temperature down and try it. Thanks

[@davebaber5371]

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

[@huey_UK]

You'll need a calculator with a 'y to the power of x' button. Type 0.5, then press the 'y to the power of x' button, then type 1.3, then press the '=' button. In this example, y=0.5, x=1.3 The 'y to the power of x' button has a normal sized 'y' with a smaller 'x' to the top right of the button. HTH.

[@davebaber5371]

@@huey_UK Thanks Adrian

[@jockster5525]

Awesome efforts thanks to you all 😊😊

[@AllenHart999]

Thank You

[@neilgordon3373]

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

[@Benzknees]

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

[@irwinxu5099]

Easy. Just buy a cheap electric heater with several heat settings or adjustable thermostat, and see how much power it needs to heat up the room to the ideal temp. That power the electric heater consumes after room temp gets stable is the heat loss of your room.

[@LabRat6619]

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

[@RaxTubeYou]

Can someone please explain the 1.3 factor, why 0.5 x 1.3? The 1.3 I do not understand. I understood The 0.5 is to go from 50c to 25c

[@MrDougie1403]

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.

[@Jhhhf4479]

Well boilers run more efficiently at different temperatures.

[@sal2883]

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

[@deanchapple1]

Mr Combi does a radiator sizing app called ‘heat loss’

[@jimrs2k]

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

[@busterpooch6941]

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. ?

[@drcl7429]

It means you need better insulation or bigger radiators.

[@SD-Plumbing-Heating]

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

[@AllenHart999]

Not sure what you are asking? What boiler do you have. Thanks.

[@SD-Plumbing-Heating]

@@AllenHart999 A worcester greenstar junior. Just one temp dial for the heating.

[@SD-Plumbing-Heating]

As for calculating the heat loss for a room before sizing a radiator, it's something I have never done. Most of the houses I work in are solid walls, as is my house very poor insulation, and it's the customer who always wants bigger rads because rooms are always cold, and running the boiler up high.

[@Bandits_At_3_o_Clock]

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

[@westleyleake699]

It depends on the heat requirements.. Wider deltaT = Lower flow rates = smaller pipe sizes

[@jessielees]

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...

[@SuperJimic]

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

[@SuperJimic]

A response to this would be great. Thanks

[@GavinWallace18]

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.

[@mikebarron4929]

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

[@AllenHart999]

Condensing combi boilers. You wouldn’t want to be turning a heat-only or system boiler too low. Thanks.

[@normanboyes4983]

@@AllenHart999 I believe t’other way round. All condensing boilers be they system or heating only should be DT 20 Flow 55 and Return 35. A system boiler implies PDHW and they would have two settings one for heating one for hot water - well the V200 would anyhoo.😉 However, a non condensing boiler should not be turned down to these temps as it will rot out the hex. Customers also need to be forewarned on these lower flow temp systems that the idea is ‘long and slow’ and with a room DT of 30 or even DT 25 the rads will not be as warm as before - but that’s OK the house will get and stay warm.

[@AllenHart999]

@@normanboyes4983 PDHW doesn’t suit everyone. I know some of the newer people into the industry are doing videos on it, They are saying this is amazing but it's nothing new. Wouldn’t really suit me on my system. It is definitely a good option though. We have a video coming up on this soon, Might be the next video. Thanks.

[@handle1196]

@@AllenHart999 hi Alan, Are you saying a new build with a system boiler cant be ran at 55 flow, only combis?

[@robertsmart7484]

Isn't it illegal to install a non-condensing boiler nowadays?

[@MrDougie1403]

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

[@alimack5489]

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

[@edc1569]

Yes, heat-pumps and low temperature systems needs to be designed properly otherwise they won't be efficient or effective.

[@AllenHart999]

Why wouldn’t you. It will set you apart from others that do not do it. Thanks.

[@normanboyes4983]

Are you expecting installers to be paid for a professional service?

[@Swwils]

@@normanboyes4983 the utilities will simply provide the capital and do it themselves from a position of leverage - all the independent engineers that don't keep up will be kaput!

[@rodgerq]

It's part of the job, why wouldn't an installer do the job fully?

[@hvaccuffingit6471]

We did a video on this point for customers as it’s a big subject to get across to them. Check it out. kzbin.info/www/bejne/pZjceH2oZdhnr5I

[@andisylafeta299]

Minute 05:00 you mention that the radiator will give an output of 1231 watts of heat every second, and I have noticed that you have claimed the same thing in other videos as well. Don't you mean that it will give an out put of 1231 watts per hour. If it were to provide an output of 1231 watts per second that would be 4000 kW per hour of heat emittion.

[@ianross5019]

1 watt is 1 joule per second. Watts are always measured in seconds.

[@2468pdv]

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.

[@Swwils]

Depending on your house it may well be more cost effective to maintain a setback temperature constantly rather than turning the heating off.

[@neilgordon3373]

I design large LPHW heating systems and the best type of heat emitters for thermal comfort is low temperature underfloor heating pipe coils. You do require more heating cross sectional surface areas for low temperature systems, for example a living room floor would require the majority of its floor area for underfloor heating pipe coils. Both radiator system and heating coil system would still have the same heat output,