Siting an heater.

[Weatherlawyer]

OOPS!

Forgot to cross post. Messages from a thread in UK.d-i-y:

My university physics is quite up to date, I don't recall the rules changing over the past 50 yrs.

Just do a few calculations and then take the trouble to measure the actual practical results. The theory of heat reflection is not particularly effective over a distance of two inches from another surface with substantially the same emissivity. Radiators on outside walls placed under windows simply increase the heat loss from the room and contribute little or nothing to the cross room temperature gradient.

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So you think but that only goes to show you are losing your marbles and may soon join Dribble in never-never land where reality is whatever you want it to be.

My university physics is quite up to date, I don't recall the rules > changing over the past 50 yrs.

Well there my have been one or two changes along the way particularly with units. Even ISO metric is different in some ways to the cgs and mks we were taught at school.

Just do a few calculations and then take the trouble to measure the > actual practical results. The theory of heat reflection is not > particularly effective over a distance of two inches from another > surface with substantially the same emissivity.

Right total emissivity of aluminium at 100C 0.09, oil paint 0.92 -

0.96. Whoops stupid reference book must be wrong. Capitol has decreed that they should be much the same.

Radiators on outside > walls placed under windows simply increase the heat loss from the room > and contribute little or nothing to the cross room temperature gradient.

In the real world there is a temperature gradient from the heat source to the environment at large (unless the heat source is largely radiant).

In the simplest example where the interior walls of a room are heated to the same temperature on both sides there would be no heat loss through the internal walls and little or no temperature gradient across the room if there was a full width radiator across the outside wall.

Reverse the situation with the radiator across the opposite wall and you will get a significant temperature drop across the room. The more poorly insulated the outside wall, the bigger the drop and the larger the convection currents within the room.

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Sort it out will you chaps? (Not you Uncle Schwartz. You can ****-off!)

[Dave Fawthrop]

| > My university physics is quite up to date, I don't recall the rules | > changing over the past 50 yrs. |=20 | Well there my have been one or two changes along the way particularly | with units. Even ISO metric is different in some ways to the cgs and | mks we were taught at school.

You were taught cgs? I was taught physics in *Imperial", in the UK.

Just seen that this is crossposted to sci.physics, so no doubt there are Americans here who still use Imperial. They lost a spacecraft with a c*ck up between Imperial and Metric.

--=20 Dave Fawthrop =20 "Intelligent Design?" my knees say *not*.=20 "Intelligent Design?" my back says *not*. More like "Incompetent design". Sig (C) Copyright Public Domain

[Douglas de Lacey]

I was taught Imperial, and the "new" SI, by a teacher who snorted "the only 'si' unit worth anything is psi!"

Douglas de Lacey.

[Roger]

The message from Dave Fawthrop contains these words:

I was taught Imperial as well but there was at least one gap. That well known unit 'the slug' didn't get a mention.

[Capitol]

Good try!

The above just goes to show the folly of quoting pure theory with no practical experience.

1) Never heard of oxidation? (and a layer of dust!) 2) At 100C( too high for the real world), E is prop to temp to power 4. The wall is at a lower temperature than the radiator.

As I said, go and measure it after you have done the sums.

Regards Capitol

[Capitol]

Just a further point, emissivity of metal surfaces with one coat of paint 0.4.

Please get all the data.

LOL

Capitol

[Roger]

The message from Capitol contains these words:

I would discount the dust but and would not expect heavy oxidisation in the home environment but even heavily oxidised aluminium has a total emissivity of 0.20 - 0.31 so no cigar.

Sorry but I don't follow your reasoning. At 70C (343.15K) 0.94 would reduce down to 0.67 but at 10C 0.09 would reduce down to 0.03 and 0.20 -

0.31 to 0.07 - 0.10. Even if we assumed the wall was at the same temperature as the radiator the disparity is still very great.

Now that would be a problem, no aluminium behind my radiators. That particular round tuit is sitting directly under a much larger one, one so large that I may never get round to it. Namely insulating the walls.