# Heat Limit to capabilities?

1. Jul 19, 2011

### Barchie

Hey All,

Maybe a silly question, but... Is there a limit to how much a certain element can heat a body of air, say a room or an oven?

Maybe more clear with an example.

If i had a candle lit in the corner of my room for ever, would the temperature of the room continuously rise (slowly) until it reached the temperature of the flame?

What would the limiting factor be? The temperature of the flame? The size of the flame? The size of the room?

(Assuming there was not heat loss from the room...)

2. Jul 19, 2011

### xts

Amount of oxygen contained in the room. If you want to ventilate it - you must revise no-loss assumption.

No-loss assumption is several orders of magnitude non-realistic if you think about candles and rooms.

3. Jul 19, 2011

### Barchie

Fine so if the losses from ventilation never outweighed the heat being provided by the candle would the room eventually one day reach the temperature of the flame? (if the candle burned forever)

4. Jul 19, 2011

### xts

If you ventillate such that you just remove some of the hot air (full of CO2) and provide fresh air at room temp and more candles, you have a stationary process: cool_candle+cool_air=>hot_hot_air_at_the_flame_temp, which hot air will finally fill the whole room.

5. Jul 19, 2011

### gsal

this candle thing opened the door for too many arguments....let's just use an electric filament! No need for oxigen.

and yes, the gas/air in the room will eventually get as hot as the heat source but it will approach it in an exponential manner since the hotter the gas the less heat it absorbs from the heat source. In other words, the heat transfered from the heat source to the gas is proportional to the temperature difference.

6. Jul 19, 2011

### DaveC426913

Yes, candle won't work as there are confounding elements. Not just oxygen but also limited fuel (it's only a candle, it'll burn down). To eliminate these problems without totally going to an electric element, you'd need to supply oxygen and some flammable gas. Now you've got an unending heat source!

Of course, you've still got to vents the byproducts somehow, or your room will eventually burst from pressure...

Hm. So an electric element is a mroe expedient heater...

As gsal points out, the next problem is that your room will start to radiate heat. The hotter it gets, the more it will radiate. This is the limiting factor. You can insulate all you want, but there is no such thing as a perfect insulator.

But if you managed to maximize insulation, then eventually the temperature in the room will reach the temperature of your heater. It will not go higher than that.

So the maximum temp of the room is limited by the maximum temp of your heating unit.