12000 BTU radiator needed?!

[d000hg]

We have some fugly, huge radiators in the two front rooms of our Victorian house. Both rooms are approx 15foot square, 9'6" ceilings with external double-brick (uninsulated) walls on 2 sides and single glazed bay windows 6-7sq m per room.

Existing radiators are double panels 54cm high, 195cm long dominating the whole walls they sit on - assume previous owner renovating the place just bought the biggest damn things they could find.
I don't have kWH/BTU figures for them and can't even find anything that long, but am guessing new ones would be rated about 3kW/10,000BTU?

Thing is, a calculator online suggested I need more like 13,000 BTU (3.5kW). We want to replace them with taller, narrower, nicer ones to get some wall space back. I was looking at tall (1.8m) narrow ones instead... personally I like them but I don't know if they are in keeping... would older properties have used these?

 

[dilalio]

would older properties have used these?

No

 

[d000hg]

Can anyone help me guess the rating on my current radiators? As I said the panels are basically 200x50cm and look like this...

I can look up new radiators if similar size and appearance but mine are at a guess 20-25 years old and I've no idea if things have moved on... Or if they might have degraded over time.

 

[jackthom]

I have similar age Myson Round Top panels in my house and they’re still throwing out the heat just fine.

Take a look at the specs for Myson Premier HE type 22 and you will find a list of sizes and heat outputs for panels very similar to the radiators you have.

http://www.myson.co.uk/products/premier_he_imperial.htm#tab-2

 

[John D v2.0]

If you have a condensing boiler you need over size radiators anyway, so make sure when you check the heat output available you're using the right temp difference.
Of course the rad sellers assume the maximum temperature when advertising the rads.
I went for much larger single panels rather then smaller double panels, to make the heat more even and it won't matter if we cover them in furniture a bit.

 

[d000hg]

Assuming mine is a double convector then that link says theirs are rated up to nearly 12000 @ 50... IS that what I've got in my photo?

Temperature wise, all I know is when they're running full blast, they're too hot to touch for more than a second or so, but not so hot they'll immediately burn you like old school heating pipes. So... 70C?

 

[jackthom]

Yours look to me like they are the double convectors and the newer 530 x 1962mm in the list I have is rated at just under 10800.

 

[John D v2.0]

Probably is 70c which is wasting gas, if you can get away with it your condensing function will be used if you turn it down to the minimum acceptably, ideally around 55 to 60.

 

[d000hg]

But then my radiators are less powerful!

Why is it less efficient by the way? It's fairly modern so I think I can set the temp. I wonder if it supports OpenTherm...

 

[John D v2.0]

But then my radiators are less powerful!

Yes that's why they have to be bigger. There's a linear relationship between temperature difference and heat transfer rate ie power. So if you lower the water temperature you need bigger rads.
The rest of the heat just carries on round the closed radiator circuit and comes back later so isn't wasted.

Why is it less efficient by the way?

Because the relationship also applies in your boiler*. The bigger the temperature difference between the burner and the heat exchanger (water) the greater the amount of heat transferred.
However the difference here is the rest of the heat just goes out the flue and is lost.

* Actually it's much more significant than that, because you also get back the latent heat of evaporation of t water in the flue gases, which is quite a lot. Hence "condensing" boiler being more efficient due to getting that energy back.

 

[endecotp]

Why is it less efficient by the way?

The temperature of the flue gas will be higher when the water temp is higher, so more energy goes "up the chimney".

 

[d000hg]

Given that my current radiator is presumably about 10000btu, which calculators say is barely enough, and already takes up (blights) the whole wall I'm not keen to get an even bigger one!

Though 70C would give me a 50C Delta even at the point is warm, so presumably I could drop 5-10C.

I imagine my boiler is a condenser but I don't know. I'll have to try and find the model.

 

[John D v2.0]

Well, our heat demand is not so high, but think laterally. We changed one double, 6 foot wide by 2 foot high rad for 3 singles 1800 wide by 300 high spread across the two outside walls. Nice even heat with no draughts, and it doesn't matter if the furniture covers some parts because they're low temperature and keeping the cold walls of the room warm. The thickness is minimal.
In your case you would need more like 1800x600 but either way it would work better.
Another option is a myson or smiths fan convector, a bit of noise but very compact. You'd need a couple of the bigger capacity one though.