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I just saw some energy saving tips, one of which was, Don't put large items of furniture in front of radiators because they absorb heat.

So, they absorb heat. Then what do they do with it, send it to the Twilight Zone?

They probably waste some of it. Expansion and the like maybe?

They don't radiate that heat as efficiently as a radiator.

Oh, & keep your socks on tonight, please. That mental image is deeply troubling.

You have to heat them up which uses energy.Keeping them at that temp uses energy. So you need more energy to heat the room.

So the furniture keeps getting hotter and hotter?

If it uses energy to expand, surely it releases energy when it contracts.

But that might not be when you want it to.

Or... Energy comes in a variety of forms, heat energy is not the same as kinetic energy, the creaks from the sofa as it expands and contracts also convert some of that heat into sound.

Any of that make sense? I've got man-flu and am still attempting to get my head round how to explain cogito ergo sum to a 9yr old.

"...and this perpetual motion machine she made is a joke. It just keeps getting faster and faster."

(http://foo.ca/wp/wp-content/uploads/2007/07/spoilers.jpg)

I like the bolded bit. that's a good sound argument, not sure if it supports the 'saving energy' cause though.

The rest is bollocks obv

If you have a radiator, you want it to heat the air in the room, not the back of a bookcase. Any heat absorbed by the bookcase will be stored until the room cool, when the heat goes back into the room, albeit at a slower rate than it did from the radiator (as it's not as hot) and at a time when you probably don't need the extra heat (as you've switched the radiator off).

So the bookcase is actually saving the energy for later, like a storage heater?

Yes but not as effectively.

Oh yes it is  :P

If the wardrobe absorbs exactly 10 units of heat, (lets call them calories) it will release exactly 10 calories of heat.

But it doesn't store the calories (AKA BTU's) for as long as a storage heater can unless the sofa is made from ceramic bricks or the storage heater is fan assisted and malfunctioning.

So it stores them for a short while and then releases them. Absolutely nothing lost. How efficient is that?

If I remember correctly, in thermodynamics terms heat is the transfer of thermal energy from one place to another. Radiators work by heating the air next to them, then the air moves somewhere else and some cold air comes to take its place, which then gets heated. If you put a large object next to the radiator, it gets heated up but it doesn't move. Because thermal energy transfer is proportional to the difference in temperature between the two objects, the radiator doesn't disperse any more energy into the room because it and the big thing next to it are at the same temperature.

Or something like that.

So then the large object is heating the air next to it, yes?

Radiators heat a room through convection as Skippy said. You stick a bookcase in front of the radiator and it heats up and retains the heat (energy). If you went and sat on a shelf on the bookcase, you'd be nice and warm most probably (and you'd probably be fairly small).

However, the rest of the room wouldn't be heated as quickly, because you're stopping the flow of warmed air.

Over time the heat energy in the bookcase will heat up the air around it, but at a slow rate. This rate might be the same rate that the room loses heat to the outside via the floors, walls, ceiling and doors. So you don't feel the benefit of that heat. Unless you're sat on the bookcase.

If the room was super-efficiently insulated, the room would heat up.

OK, OK. I'll move the wardrobe FFS.

Oh, it's a wardrobe.  Thought it was a bookcase.  That changes everything.