radiator sizes

[Stephen]

Hello,

I was asking about radiators on the "CH pipe size" thread but the discussion has moved on to radiator sizes rather than pipe sizes, so I thought a new thread would be useful.

I just wanted to ask two last questions:

Is 300W a noticeable difference in heat output: I have found two radiators for sale and their outputs differ by 300W, would I notice the difference?

Is there a big difference between makes on panel radiator regarding their outputs? Sorry to switch units but I was looking for a rad about

7000BTU and I see some makes I can use a 500x1300, others require 500x1400 and others 500x1600. Different makes of 500x1400 have different outputs (hence question one above).

Thanks in advance. Stephen.

[Roger Mills]

It depends on what percentage change this represents! You'd be more likely to notice the difference between 300 and 600 than between 2300 and 2600.

To at least a first order of approximation, all radiators of a given size and construction should give the same output under the same (Delta-T) operating conditions. The output depends on:

• surface area of the panels and fins

• emmissivity of the surface finish

• mean surface temperature

None of those things are going vary all that much from make to make. There may be slight variations depending on the spacing and depth of the fins - which could have an effect on the amount of convected heat entering the room.

There are rules of thumb for watts per square metre for each basic type - single panel without fins, single panel with fins, double panel without fins, double panel with single fins, double panel with double fins, etc. Most manufacturers' published data fit in with the rules of thumb fairly well - although some manufacturers do quote different outputs for different shapes[1] even though the areas may be the same.

Are you sure that all the examples which you cite are specified at the same dT?

[1] e.g. 2000 x 300 vs 1000 x 600

[Stephen]

Very true! I shall have to calculate the percentage difference.

That's what I thought, which is why I was surprised that the outputs differed. Perhaps some marketing departments "tweak" their figures more than others?

I am currently looking at a Quinn Barlo 500x1400 double (2.3kW, 7900 BTU IIRC). Is Quinn barlo a good make? I think it's the least I can do, since Barlo were kind enough to provide the calculator ;)

I have looked at other makes 500mm high and double width to produce the same output; one required 500x1600 but another managed with just

500x1300. I am surprised that 160mm in one outputs as much as 1300mm in another; I would have thought a foot difference in length would have made a big difference to output.

Yes, after all your previous help with factors, I checked, double checked and checked again! Only Toolstation and 4bathrooms quote dT=60, everyone else is using dT=50

Thanks again. Stephen.

[David]

Quinn Barlo are good, we have had one of their radiators for 6 years, very well made and solid.

[Roger Mills]

Would you care to define "double"? Some doubles have *two* sets of fins - back to back on both panels - (K2 in Stelrad parlance) and some have just one set (P+) - and it makes quite a difference to the output. Just looking at a Stelrad data sheet, a 1200 x 450 K2 has a very similar output to a 1600 x 450 P+.

Are you sure that you're comparing apples with apples?

[Roger Mills]

I'm sure they're as good as anyone else's. I tend to regard radiators as a 'commodity' purchase - they're all much of a muchness - so unless you're prepared to pay through the nose for a pretty looking 'designer' jobby, go for the cheapest. Whatever you go for, there are some good on-line deals which are a lot cheaper than anything you'll get at the sheds.

[David]

The Altech ones from Graham are poorly made.

[Stephen]

Thanks. That's what I thought, as I said in an earlier post, the standard panel; ones all look the same to me.

The ones I had looked at were all double radiators with double fins and all 500mm high.

The web sites all list output in BTUs, I have divided by 3.413 to calculate the Watts.

Kudox (at B&Q) 500m x 1400mm has a 7053 BTU (2.07kW) at dt=50 Quinn 500 x 1400 is 7941 BTU (2.33 kW) Myson 500 x 1400 is 7094 BTU (2.08 kW)

I cannot understand why the Quinn is so much higher than the other two.

The Biasi from 4 bathrooms is the only one rated at dT=60. At dT=60 the output is 8505, which by my calculations (divide by 1.27) equates to 6697 BTU (1.96 kW), which seems a little lower than the others. Why?

Any offer/merchant you recommend in particular?

Thanks again. Stephen.

[Stephen]

Sorry, I should have added that the Barlo calculator says I need 2.2kW or 7473 BTUs, so this is why I am anxious about the outputs of the rads. The Kudox and Myson would be below this but the Quinn would be ideal for my requirements. However, is the rating for the Quinn too good to be true? I could buy a 1600mm rad just to be sure, but I would like to keep the length and cost of the rad as small as possible!

Thanks.

[Roger Mills]

No, nor can I! Would you care to provide URLs for each of the 3 sites?

The last time I bought a radiator (about a year ago), I got it from

They were very competitive at the time. They took a few days to deliver 'cos they don't hold any stock, but use local merchants. [I think it was delivered to me by the local branch of PlumbCenter - but at a much lower price than if I had gone direct to them.]

I've also had a few from Screwfix - but they only do (or did) a limited range of sizes. ISTR that they didn't do any that were more than 600mm tall, and I wanted some at 700.

[YAPH]

suggest you check the article on radiators in the wiki - it has a formula for working out the output of any standard rad given its sizes and configuration

[Stephen]

But that was my question. If all radiators that are the same height, same width, and all double finned, why should one make have a higher output. If they are all constructed the same and obey the same formula, should all outputs be equal?

[Stephen]

(h)500mm&x=28&y=14>> Quinn 500 x 1400 is 7941 BTU (2.33 kW)

> Myson 500 x 1400 is 7094 BTU (2.08 kW)

> I cannot understand why the Quinn is so much higher than the other >> two.

[The Natural Philosopher]

The heat output of a radiator is also critically dependent on its working temperature and the ambient temperature. So the same rad can have many different outputs depending on how its measured.

If it was red hot, it would output a fair but more..

[Roger Mills]

Yes, we *know* that - but manufactuers' published data should surely all be based on measurements made under the *same* operating conditions - certainly when they quote the same delta-T.

[Roger Mills]

(h)500mm&x=28&y=14>>>>> Quinn 500 x 1400 is 7941 BTU (2.33 kW)

>>>> Myson 500 x 1400 is 7094 BTU (2.08 kW)

>>> I cannot understand why the Quinn is so much higher than the other >>> two.

Thanks for the URL's. I'm afraid they don't reveal any obvious reasons for the differences.

My own rules of thumb would give a figure of 2000 watts at dT=50 (or 2500 watts at dT=60) for that size of radiator - which stacks up quite well with

2 of the 3 offerings. My immediate thoughts were that the Quinn/Barlo one may have been measured at 60 even though they claimed 50 - but that would take it to 2500 instead of 2350. I suppose they *could* have measured it at 55 - that would be closer, but still not quite right.

In any event, I would be inclined to suspect the Quinn figures. Unless they've found a clever way of defeating the laws of physics, their design is unlikely to be 15% better than everyone else's.

[Stephen]

From Quinn: "I can confirm that the output is correct this is due to our design of the vertical water channels being at a market leading pitch of 25mm combining our convection fin configuration gives us a high performing radiator."

I may still go for the 1600mm, just to be sure.

[Stephen]

One last question: I have been using the Barlo calculator to calculate the radiators I need. I am unsure what to do about the hall. Aren't hall, stairs, and landing all one thing? Heat from the radiator at the foot of the stairs will rise. How do I go about entering ceiling heights and wall lengths to get a suitably sized radiator (there is no radiator on the landing). Thanks.

[Roger Mills]

You need to do it as several bits - just as you would an L-shaped room - and add them together. So you'll have a downstairs bit, an upstairs bit and a two-storey bit where the stairs are. Obviously where two bits meet in fresh air, you need to create a 'wall' which has a U value of zero - but the temperature will be the same on both 'sides', so it doesn't really matter.

[Stephen]

That's what I thought but I wanted to double check: I am doing the right thing by specifying the hall radiator to heat all of the hall, stairs, and landing?

The stair section will be triangular because at the bottom of the stairs the height is two storeys but at the top it is only one. What is the best way around this? Use a measurement of half the base x the height?

I had a look at the heatingshop url you gave but their web site is confusing; it would be easier if you didn't have to add supplements depending if you bought a single, double, or one and a half size radiator.

BTW did you see the reply from Quinn; what did you think?

Thanks again.