Towel Radiator Electric Element wattage?

[Charles Fearnley]

Just wondered if anyone has some experience here of the effect of different wattage elements used in a towel rail?

We have an onsuite bathroom with wet underfloor heating, which is nicely warm in the winter. Towels are hung on a multi-S shaped towel radiator, which currently has no heat input - we just liked the shape. Towels dry nicely in the winter, and during properly warm weather. However, in spring/autumn when the heating is off they can seem a little damp, so I'm intending to add an electrical element, fed from a timed spur, to the rad.

I don't have any info on the rad - special offer, no paperwork. It is multi S shaped, with about 9 metres of 20mm pipe horizontally, and two 1.4 metre verticals of 25mm pipe, all chromed steel.

Electric elements come from 150 watts to 600 ish. I'd like it to warm gently for a couple of hours, rather than be hot, as no room heating is needed. I thought 200 or 250 watts? Any experience here? Another reason for keeping the wattage lower is that SWMBO is good at turning things on, and rather less good at turning them off.....

Also, the rad will be filled with water, with a decent dose of inhibitor. It will not be connected to the central heating proper. Do I get it up to full temp to expand the water, and then close the top vent, or do I leave the vent open a little. If closed, is an air bubble for expansion at the top a good idea?

Thanks for ideas,

Charles F

[Dave Liquorice]

Look at the spec for the raditor and find out its nominal output when used ona CH system. Then is if 1/4 of that seems sensible?

You can get "push for heat" towel rail switches that come on for a period of time. Some allow 1/2 hour, 1hr, 2hrs.

Essential, don't under estimate the strength of expansion forces. Any real reason not to plumb it in? Water with inhibitor ought to be OK but don't seal it straight up allow it to "breath" for a while to let the dissolved air out. Perhaps boiled water wouldn't have much dissolved air left? Water isn't normally used for stand alone electrically heated rails, some for of oil is (with expansion gap). Think I'd at least look for a suitable oil rather than use corrosive and conductive water.

[NT]

If all you want is minimum heat to aid drying a little, I'd think 150w would get it hot and do that. If you prefer you could have a 2 heat setting switch, one feeding 240v ac, the other via a suitably rated diode, and use a higher power element.

NT

[Charles Fearnley]

If all you want is minimum heat to aid drying a little, I'd think 150w would get it hot and do that. If you prefer you could have a 2 heat setting switch, one feeding 240v ac, the other via a suitably rated diode, and use a higher power element.

The diode sounds a good idea, and yes, 150/200 watts should probably do it.

Dave L's idea of 25% of nominal output is sensible, but unfortunately when bought as a special offer with no paperwork I don't know what that is, and guesstimating BTU's is more difficult than with conventional radiators because of the variation in formats.

I've seen a suggestion that leaving 10% of capacity as air will allow for expansion, so will probably try that. I'll also investigate 3 bar safety valves. Plumbing to the heating system isn't easy, as the bathroom was designed for underfloor heating and pipework is now fairly inaccessible.

Thanks to both.

Charles

[Nick Odell]

Ice at 0 deg C expands by roughly 9% over the volume of water at 4 deg C, so if you want to allow for freezing then 10% is a good figure, yes. Water will expand by roughly 3% between 4 deg C and 80 deg C so if you are confident that all the temperatures are going to be positive then 4% should do it.

[NT]

A simple option is to not do the bleed valve up tight. 5% expansion with 10% headspace =3D 2 atmospheres!

NT

[Dave Liquorice]

ICBA to check the maths but two atmospheres isn't very much. Most radiators and plumbing stuff is speced to 10 Bar, 10 atmospheres give or take a bit.