Heat Loss - Pen & Paper Check

[Diggory]

Thanks reply.

I was concerned that because it has a high thermal mass (big lump masonry), I would need to assume something like a 10 or even 21 deg temp differential.


D

 

[Diggory]

Thanks to advice gratefully received, I’ve generated my radiator shopping list (from U values / areas etc and no Apps).
I wanted to check against rads that came out (sensible advice from @oldbuffer) that I’m in the right ball-park.
I get the feeling the new rads are a tad larger capacity wise.

Trouble is, they are quite old rads and I can’t seem to find equivalent listing on line.
The type 22s I’ve found similar on stelrad site (their K2 listings).
But the type 10s (single panel no fins) and type 20 (double panels no fins) don’t seem at all popular.

Grateful if someone would give me a steer as to where I might find W/BTU values.
Or if someone experienced might suggest a rule of thumb value.

Thanks D

 

[Notch7]

Thanks to advice gratefully received, I’ve generated my radiator shopping list (from U values / areas etc and no Apps).
I wanted to check against rads that came out (sensible advice from @oldbuffer) that I’m in the right ball-park.
I get the feeling the new rads are a tad larger capacity wise.

Trouble is, they are quite old rads and I can’t seem to find equivalent listing on line.
The type 22s I’ve found similar on stelrad site (their K2 listings).
But the type 10s (single panel no fins) and type 20 (double panels no fins) don’t seem at all popular.

Grateful if someone would give me a steer as to where I might find W/BTU values.
Or if someone experienced might suggest a rule of thumb value.

Thanks D

Wickes are a good place to get Stelrad radiators at great prices -cheaper than from stelrad themselves

you havent mentioned if you are replacing the gas boiler -if you are, I would recommend going for an option where you can a lower flow and return temp -as the lower the temp the more efficient the heating will be and a more comfortable heat.

if you can get a flow temp of no more than 40 deg for say 90% of the time, that would be good

obviously rad size increases with low flow temps and poor insulation.

 

[Mister Banks]

Thanks to advice gratefully received, I’ve generated my radiator shopping list (from U values / areas etc and no Apps).
I wanted to check against rads that came out (sensible advice from @oldbuffer) that I’m in the right ball-park.
I get the feeling the new rads are a tad larger capacity wise.

Trouble is, they are quite old rads and I can’t seem to find equivalent listing on line.
The type 22s I’ve found similar on stelrad site (their K2 listings).
But the type 10s (single panel no fins) and type 20 (double panels no fins) don’t seem at all popular.

Grateful if someone would give me a steer as to where I might find W/BTU values.
Or if someone experienced might suggest a rule of thumb value.

Thanks D

Size the radiators for a DT30 rather than DT50

 

[dilalio]

Replacing all rads or installing new system then they have to be sized for low temperature heating to meet building regs.

Max flow temp of 55°C

 

[Diggory]

Thank you @Notch7 and @Mister Banks for reply.
The boiler has (just) been replaced; ecoFIT pure 825 combi; 25 kW / 85,000 BTU.
(Old boiler was Potterton 60e 18Kw).

New boiler plumbed with two zones:
- Z1 17sqm UFH installed and running now.
- Z2 x9 rads; flow/return not yet connected - radiators being replaced.

By modern standards; house insulation isn’t great (parts are >200yrs).
Mix of solid walls and cavity (of sorts) walls, single glazing, sketchy loft insulation, gaps, drafts……….
I can make some improvements over time but fundamentally - I can’t see me ever looking at heat pumps.
Which is kinda why I was happy to work on T50 specs.

I was trying to check my new sizes with previous rads (as advised by @oldbuffer) and I simply can’t find type 10 or type 20.
Could I assume that the fins on a type 22 make it ?% more efficient than type 20 (double panels no fins).
…….that the fins on a type 11 make it ?% more efficient than type 10 (single panel no fins)
Are there any rules of thumb for estimating their output - like Watts per linear metre ?

Thanks D

 

[endecotp]

I can’t see me ever looking at heat pumps.
Which is kinda why I was happy to work on T50 specs.

It’s not only heat pumps that benefit from larger rads; condensing boilers only actually condense when they operate at lower temperatures than older boilers did.

Here are your boiler’s efficiency numbers for different temperatures:

https://www.vaillant.co.uk/product-images/0020230531-07.pdf.pdf

Note that the greater-than-100% efficiencies are because “100% efficient” is based on the best that a non-condensing boiler can do, i.e. steam coming out of the flue. A condensing boiler also recovers the latent heat of the steam and produces liquid condensate water.

Now we have to avoid the confusion of “delta T between rad and room” and “delta T between flow and return” at this point. I think - and maybe someone can confirm - that when you say “T 50” that means “room is 20 C and average rad surface is 20 + 50 = 70 C = mean of flow and return”, which is 80/60 in the table. And “T 30” means “room is 20 C and average rad surface is 20 + 30 = 50 C = mean of flow and return”, which is not even as good as the second row of the table. To have your boiler running as efficiently as possible - which will be 10% cheaper than you are currently proposing - you need even larger rads.

Sorry, I don’t know the output for your old single rads.

 

[Diggory]

Thank you @endecotp……..

The STELRAD data I’m looking at qualifies the T50 with ‘(75/65/20 deg C)’ .
So the T50 is the delta of room temp at 20 deg C to the rad temp 70 deg C (being the mean of 75/65 flow & return).

if I understand correctly - there is an opportunity here to make the boiler upto 10% more efficient by lowering the flow/return temps.
Consequently, I’d need physically larger rads to still get the same / required Watts.

I’ll see if I can source the T30 / T40 sizing data.
My (new) rads are pretty large in the available spaces at T50 sizing - will T30 / T40 supersize things ?

Thanks D

 

[endecotp]

will T30 / T40 supersize things ?

Yes; almost double. If you had a single panel, a double of similar size is needed. If you had a double already - well, I guess that is what triple rads were invented for?

 

[Diggory]

If I’m calculating correctly……….
One of my rooms has two rads set against requirement of 2,668W.
My plan was (reading off the DT50 75/65/20 degC Table) 2x 1,400W Type 22; 450(h) x 1,100(w) = 2,800W (I can’t go taller than 450mm).

Factored for DT30; the I’d need the equivalent of 5,202W (reading off the same DT50 75/65/20 degC Table).
The 450(h) Type 22 rads max out at 1,800(w) = 2,291W (so 4,5682W for two but still 620W short of what I’d need).

I like the efficiency angle but the practicalities might be challenging.
This kinda suggests that DT30 will broadly double my rad sizes ?

D

 

[Diggory]

Sorry typo
(so 4,5682 4,582W for two but still 620W short of what I’d need).

 

[Diggory]

Yes; almost double. If you had a single panel, a double of similar size is needed. If you had a double already - well, I guess that is what triple rads were invented for?

Sorry, I missed that reply; then figured it out myself 15mins later

If I didn’t go the DT30 route; is it just that I’m not taking the opportunity to improve efficiency.
And if I size of the DT50 data, it will suffice albeit at perhaps 10% less efficiency.


Thanks D

 

[endecotp]

It is also a buildings regs compliance issue.

 

[Diggory]

It is also a buildings regs compliance issue.

I’m only altering / repairing an existing system ?
Replacing the 40yr old rusty / sludge rads (and trying to get sizing correct).

And the boiler and UFH has been installed by a ‘competent person’.
The same person will be fitting / flushing / commissioning the rads.

D

 

[dilalio]

I’m only altering / repairing an existing system ?
Replacing the 40yr old rusty / sludge rads (and trying to get sizing correct).

Conservation of fuel and power: Approved Document L

Building regulation in England setting standards for the energy performance of new and existing buildings.

www.gov.uk