Speccing radiators at the moment.

taking a sample 5.0m x 6.0m bedroom with 2.4m ceiling height. House is very well insulated (new build U=0.27 wall, 0.14 roof etc) gives me a a fabric heat loss of about 140W/h. Now, Im planning on a whole house heat recovery system, so if assume one air change an hour but 75%+ heat recovery implies something like 320*25% vent loss i.e. about 80W/h. So a total requirement of say 220W/h or 6,500 btu.

That's a 1200mm x 600mm aluminium radiator which seems about normal.

If I didnt have the heat recovery system or decent U-values that quickly gets to 19,000 btu or a 3600mm x 600mm radiator!??! 😯

can that be right?

Not sure about your maths but from your title, I would get a welded, not riveted radiator, smoother finish and less likely to leak.

Hope that helps? 🙂

Oh, and if you had crap insulation I guess that would mean you need a bigger radiator, doesn't seem that strange…

but a 3.6m radiator is almost th ewhole bluddy wall! 😉

I don't understand the maths ( bit thick) but why not have 2 radiators?

We've got a fairly large bedroom, double aspect,so a radiator under each window. Or am I missing the point?

aesthetics sweetie.

and my maths were a little out – I had too high a u-value for my windows.
With a bit of tweaking I reckon the largest bedroom will have a single 600mm x 1400mm radiator producing c.7500 btu against a forecast demand of 8200 btu.

Sounds too big to me, sure that decimal place is right on the Watts to BTU conversion, thought it was 1:3.4, giving you a 748BTU rad. That'll not be big enough to dry a bath towel on! That doesn't sound right either. Back to the Myson homepage.

Oh so condescending old chap 😉

My living room was always on the cold side, so I popped along to the heating/plumbing shop chap worked out the optimum radiator size for the room and then sold me the next size up and a thermostatic valve. His view was the cost of the next size radiator up is minimal given the cost of running it and fitting costs the same, thermostatic valve controls the room temperature.

Even with the latest cold weather the room was warm, so your choice is warm room vrs aesthetics

I would go for a warm room every time

❓

hmmm. well this http://www.radcalcs.com/ seems to think I need 14k btu + for a 5mx6m room.

blimey and this one http://www.heatandplumb.com/radCalcs.html with the same specs but taking into account all the insulation etc says only 3k BTU!

mad

Is that single-thickness rads or double thickness? Most large rooms I' know of have double-thickness rads, meaning you could cut your 3.6 down a bit.

Could you not add heating to the vent system and do away with the rads?

If your 220W/hr is right just leave a couple of table lamps or halogen uplighters on and ditch the boiler!

Ill just rub some sticks together downstairs 🙂

I think Ive got it now. But will double check later.
ta MLC – I think youve put me on the right path…,.

Stoner you may be looking at the wrong rads. a double panel rad would give you an output of approx 2kw which my calc says is about right for that room. Are your walls insulated ? And how many outside walls are there ?

I get a heat loss of 1.1kW.

Assuming bungalow, new build floor, new build ceiling, new build walls etc and a window size of 1.2m x 1.2m.