Using a fan and space heater to warm up a room

[Niteonites]

What follows will be a very practical question for the winter months.

I'm a senior math major who appreciates efficiency. And saving money, I like that too. As it turns out, the heater in my apartment eats money like there's no tomorrow, so it generally tends to be left off for obvious reasons.

What I have instead is a space heater and a box fan. I have been placing the fan directly behind (In front of?) the space heater and using that to quickly warm my room so I don't wake up as a popsicle. The space heater consists of 7 large metal fins evenly spaced to encourage airflow.

What impact does the placement of the fan have on the ambient temperature of the room? Am I wasting electricity for no reason by having the fan and the space heater running in tandem? Is placing the fan by the space heater optimal, or would it be better situated in a position where it can generate the maximum air circulation in my small, cube-like room?

Any help would be appreciated.

 

[Niteonites]

For details, my room is roughly 10 feet wide, 12 feet long, and 10 feet tall with minimal furnishings.

 

[terryphi]

hmm...

well the specific heat of air will decrease with temperature

http://www.engineeringtoolbox.com/air-properties-d_156.html

and change in temperature is inversely proportional to the specific heat capacity.

so as your specific heat gets smaller your change in temperature per energy gets larger.

That is it's easier to warm up hot air than cold air...so does that mean you should just have no fan?

I'm confused :S

 

[Danger]

The heat will tend to rise immediately after leaving the coil, so a fan will disperse it more evenly throughout the room. (In fact, any space heater that I've ever owned had an integral fan.) Personally, I would put the fan behind the heater to avoid it being damaged by the heat.
By the bye, be very careful when using any space heater, with the possible exception of the oil-immersion units. They constitute a serious fire hazard.

 

[mrspeedybob]

How many outside walls does your room have and how well insulated are they. As the walls conduct heat from the inside air to the outside air a layer of cold air will form next to each outside wall. The fan will serve to continually replace this air cooler air with the air that you just warmed up. A more efficient approach would be an electric mattress cover. This would keep most of the heat between the mattress below and your blankets above, exactly where you are in danger of popsiclization.

 

[Danger]

A more efficient approach would be an electric mattress cover. This would keep most of the heat between the mattress below and your blankets above, exactly where you are in danger of popsiclization.

Excellent suggestion, as to warmth while in bed. I got the impression that Niteonites wanted the whole room heated.
I'm quite a cold-blooded creature, so my mother went to a large store (the Bay, I think) to buy me an electric blanket for X-mas. She didn't find a suitable one, but the cashier asked her if she had everything that she wanted and she said "no". She explained that she was trying to find something to keep me warm, and somehow mentioned that I was diabetic. The cashier immediately said that her husband was also diabetic and that a mattress warmer worked great for him. So, Lumpy bought one for me and I used it every night until I moved in with the ex. It's so much better than an electric blanket, because (as you mentioned), the heat rises through and around you and is partially reflected back as opposed to starting above you and continuing to rise as happens with a normal electric blanket.

 

[sophiecentaur]

This is a practical question and can't be answered by 'simple' Physics. You are not dealing with an object that needs to be at a certain temperature; you are dealing with a complex system of heat flow and uneven temperature distribution.
If your windows are not well draught-proof and single glazed then you may be getting cold air dropping down onto the floor from them and giving you cold feet. That is, subjectively, a bad thing and will leave you wanting more heat than you really 'need'. Also, the heat from your heater may well be finding its way up to the ceiling region, where you aren't getting any pleasure from it.
You can reduce / eliminate this form of convection by placing your heater(s) under a window so that the coldest air isn't flowing directly onto you feet. Ideally, there should be circulation which can bring the warm air down from the higher regions down to you. Central Heating radiators tend to be placed under windows, when it's convenient, for this reason.
There is also an issue of timescale. If you just want to feel warm quickly in the morning for a short time then you definitely don't want to be heating up walls and other building fabric more than necessary. They will be dissipating all the heat you gave them whilst you are out at work. Make sure that any warm air is circulating around the room and not being blasted up against a wall. Radiant heaters can also be great at warming You up quickly, even in an otherwise cold room.
In my opinion, a high power output system would definitely be better (more efficient) than a low power output if you don't need the walls to be warm. Get this to turn on just soon enough before you get up and you'll be walking round in comfortable warm air. A low power system will be on for longer and will have time to 'waste' much of the energy on the walls.
Of course, over a long time, the whole room will reach a steady temperature and 1kWhr is always 1kWhr so the choice of method of heating is of less consequence.

 

[JDługosz]

I find that I'm warmed, apparently, by IR from halogen light bulbs, far in excess of what the room temp. would indicate. In the cold bathroom, I turn on a radiant-style heater and feel warmer in seconds, without actually heating up the room yet.

So, an efficient solution might be a heat lamp (IR, invisible) pointing at your head that is not covered by heated blankets.

I also used a IR laser-spot thermometer to find where the bedroom loses heat. Covering the windows with heavy drapes and covering any cold walls with tapestries is the "classic" approach and does wonders. I also discovered that my large bath tub is a huge heat sink! Covering it with a blanket made an instant difference, as I no longer felt the cold creeping in from it even before the room thermometer had a chance to show a 2-degree difference from doing that.

 

[sophiecentaur]

IR is incredibly effective, subjectively. A hundred Watts of sunlight on a cold day makes you feel fantastically 'warmed'. It's a pity that highly reflective walls, ceilings and floors never caught on. Perhaps we will be reduced to that when the energy crisis really starts to bite. Living in a dewar vessel!

 

[meepmeep]

Hi, I don't think you are wasting money by using the fan, since you sound like using an oil-filled radiator, which is a convection heater. It heats the air directly so by blowing the air you spread the warmth faster. On the other hand those radiators exploit such physical laws already, like warm air is lighter than cold so it floats up and gets replaced by cold air which gets heated again, this ensures natural air circulation. If you used a radiant heater on the other hand, this method of yours by fan would not even work, would make no difference - or a very little. (convection vs radiant heater)