As you will have seen, Sunray beat you to that comment, but I would psoe the same question to you as i did to him, namely...
... i.e. is this something you have seen done (for this purpose) in a domestic property?
Kind Regards, John
stupid question - infraRed
- Thread starter Tigercubrider
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Kind Regards, John
Fair enough. However, since (by implication) he seemed to be interested in gaining an understanding of the physics of "IR heating", I thought that a little more detail might be useful for him.
Kind Regards, John
Yes! Very effective they can be. They do not have to run fast, to move the air down.
They are often combined with a centre light.
Interesting. I know of plenty of combined lights/ceiling fans, but I would not have thought that (m)any of the people I know to have them would even dream of turning the fan on whilst they were using heating - since the fans are generally perceived as a means of 'cooling'.
In any event, to yet again try to get back to the point I was making, I don't think it makes much difference whether the 'radiator' is near floor level or 'half way up the wall', whether one has a ceiling fan or not.
Kind Regards, John
We can agree on that, though it is better to have a radiator on the colder wall, than a warm wall. That way the falling air is counteracted by the rising heat.
The whole point is fans do nothing to change the temperature of the air, all they can do is move it. Just look at how an air duct works.
Yes we have a ceiling fan/light in the bedroom and it gets used in the summer at a higher speed to disperse the heat collected at the top of the house (hopefully out of the open windows) and at a lower speed in the winter to move the hot air down.
Very effective.
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That' a different point, but I don't disagree with it.
Mind you, in 'efficiency' terms, if the 'colder wall' is colder because, say, it is a poorly insulated outside wall, then having the heat rising from the radiator in contact with that 'lossy' wall will presumably result in more 'lost heat'. In fact, going back again to my original point, IF one has the radiator against such a 'colder'/lossy wall, then it would probably be better (efficiency-wise) if the radiator were 'high up on the wall'.
Kind Regards, John
Of course.
... which corresponds to what most people use such a fan for, but ...
... that's what I can't recall ever having seen people doing in domestic environments. Maybe my experience is too limited!
Kind Regards, John
It's usually in the instructions... I think.
Quite possibly, but that doesn't alter the fact that I don't recall ever having seen anyone doing it in a domestic environment.
Next time I'm in a house where there is such a fan, I'll ask about how/when/why it is used.
Kind Regards, John
Most of the heat loss is via the outer walls in a centrally heated house anyway, not much is lost through internal walls.
If a radiator is placed high on an outside wall, I suspect there would still be the cold draft from cooled air falling down the wall. The most effective position is at the bottom of the cold wall to prevent that.
Of course. Indeed, if one thinks about the whole property, rather than just a single room, that which goes through internal walls is not really 'lost', since it merely heats other rooms.
I'm not so sure about that, particularly in relation to the issue I was talking about (heat loss/'efficiency'). Consider the following:
- The rate of heat movement through anything (e.g. heat loss through an external wall) is proportional to the temperature difference across that 'anything' (e.g. the external wall), and also proportional to the surface area of the 'anything' through which the transfer is occurring.
- The hottest air will will that rising from the 'radiator', in contact with the wall to which the radiator is attached.
- If the radiator is some way up the external wall, then the part of the wall above the radiator will be the hottest part of the wall, with the part of the wall below the radiator being much cooler.
- Hence, the higher up the wall the 'radiator' is positioned, the smaller will be the area of the inside surface of the wall that is 'the hottest', hence the less will be the heat transfer ('loss') through the wall.
Kind Regards, John
I've had a look around at 'instructions' 9and also some of the online discussions about this) and it is, indeed, true than many of them mention using the ceiling fan to "keep rooms warmer in Winter". Interestingly, nearly all of them say that as well as running the fan at klow speed for that purpose (if speed is variable) one should also switch the fan to run in the opposite direction ('clockwise', rather than 'anticlockwise')from that one would use in summer - so that it pushes cooler air from the room UP towards the ceiling and thereby, causing the hot air near the ceiling to be forced down (at the sides of the room). That makes sense since, as many of these instructions note, if one has the fan blowing down (as in summer) it will tend to have the same effect (as in summer) of making people feel cooler, since even warm air blown against skin results in evaporation of perspiration.
However, that doesn't alter the fact that (in many decades!) I don't recall having heard of people doing this, and certainly doesn't necessarily mean that many people actually read (and/or take notice of) that part of the instructions! This morning I spoke to a neighbour who I know has such a fan. It so happens that he is an engineer, and therefore had no difficulty in understanding the physics/logic of this when I explained, but he nevertheless said that, in many years of having the fan, it had never occurred to him to use it for such a purpose.
Kind Regards, John
I must admit, I didn't know about the advice to run them to blow up in winter. As said I don't have one, but for years I have fancied getting one for the bedroom, to help cool it in hot weather without the noise and untidiness of portable fan we presently use. I typically put the fan on the window ledge, fully open the window and have it drawing the outside cooler air, into the bedroom.
I also admit that it hadn't occurred to me, either (although I did almost mention that 'blowing air down' {even warm air} could partially have the effect of cooling skin). Indeed, I didn't even know that they had the facility to reverse direction of rotation/air flow, but it seems that the great majority do.
I've never had one, either, although I have frequently encountered them in rooms in hotels in 'hot countries' when the hotel was not sufficiently up-market to have decent AC (and sometimes as an addition, even when they do have good AC). However, that has merely reinforced my perception of their role being 'to cool', rather than to aid warming!
Kind Regards, John
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