Radiator Spec - just before I buy!

[gg]

Hi, hope anyone can help before I take the plunge and buy/arrange plumber!

I have a largish room (14 x 13ft, high ceilings) with a single 700mm x1400mm Stelrad double convector...

The rad gets very hot - although not as hot at the very bottom than the top (we have a newish Greenstart 28 boiler and thats OK) but as the house has 3 outside walls (solid walls, no cavity) and a large window (the rad is opposite the wall to the window also as its a low curved bay) - the room takes AGES to warm up to 21-22m, our desired temp.

Ive looked on the BTU calc sites, and due to the high ceiling, walls, window etc, the different cals reckon anywhere between 9,500 and 12000 BTu's for the room!

The Stelrad rad at the moment is a double convector but 10+ years old (again, gets hot and isnt leaking, but Im sure they have got more efficient over the years!)

I could actually fit a 700mm x 1800mm rad (double convector) for about =A3150 + fitting which would then cover more of the room (it would sit more central with only minor pipe extension I think)

Am I right in thinking that this would help/resolve my problem??

Anyone have an idea on how long a plumber would need to replace??

If I way off the mark and may ber wasting my money, please let me know! - I realise that the rad may need a 'flush' but as its 10+ years old and seemingly under 'BTU'd for the room, I was wondering if replacement was the best course?

Many thanks

[TheScullster]

wrote

Hi, hope anyone can help before I take the plunge and buy/arrange plumber!

I have a largish room (14 x 13ft, high ceilings) with a single 700mm x1400mm Stelrad double convector...

snip..................

Fitting one larger rad in a cold room may well achieve the desired temperature quicker - but you will still suffer thermal gradients across/around the room. For greater comfort I would consider adding a radiator as far from the existing as possible and also located to warm "drafts". If you have suspended wooden floors, this is achievable without too much hassle - concrete floors like ours is another ball game.

Phil

[Roger Mills]

As always, you need to start by reviewing the insulation and draft proofing, and doing all you can to reduce the heat losses. When do have done that you need to re-calculate the heat losses and find a suitable radiator to match them.

Looking at ny Stelrad brochure, a 700x1800 P+ has a rated capacity of 11,993 BTU/Hr (3.5kW). That is for a Delta T of 60 degC so, if your Delta T (difference between room temperature and mean rad temperature) is 55 degC (more likely than 60), you'll need to downgrade the rated value by about

10% - bringing it down to about 10,800 BTU/Hr. [The P+ is a double radiator with one lot of fins between the sections. If you need even more heat, a K2 of the same size (which has double fins) has a rated capacity of 15,373 BTU/Hr - or about 13,800 when downrated]

If you do increase the radiator capacity, you'll need to make sure that the pipework is adequate. It generally reckoned that 15mm pipe will support 6kW of heating capacity. The above mentioned K2 is 4.5kW - so you wouldn't want much else sharing the same pipes.

If you fit a larger radiator in essentially the same position as the existing one, it probably wouldn't take a plumber all that long to fit. He

*may* be able to do it without draining down if he freezes, shortens and caps off the existing pipes and then extends them again when the new rad is in place.

[gg]

Thanks for that, we do have 15mm pipes and this rad (downstairs frontmost room, furthest away from boiler) doesnt have any other radiator after it.

Hopefully it wont involve the complete draining of the system....but I will expect the worse>

Any idea how long it *should* take if a drain, refill (and additive readded) would take?

Ive been warned of a =A3200 plumbing for this as its a days work????

Thanks

[Roger Mills]

But does it have any others *before* it, after it splits off from the 22mm main flow and return pipes?

I'm sure that many plumbers could make it last a day if they have to do a drain-down.

When I partially drain my system, I aways collect the water and put it back into the F&E tank so as not to lose the inhibitor or introduce a load of new air.

[Donwill]

My understanding was that a 15mm pipe supplying 6Kw is only recomended for offices, factories and workshops, it requires a water velocity of approx 1 M/sec which would generate water flow noise in the pipes to be at an unnaceptable high level in a domestic situation. You should design for a max velocity of 0.75M/sec, a 15 mm pipe will only supply just over 3Kw for a 11deg C drop across the rad, or am I just too old fashioned and out of touch these days. Regards Don

[TheScullster]

"Donwill" wrote

If old fashioned leads to better (in this case quieter) system design, I'm with you every step of the way.

Phil