Electric heater vs. PC question

Post by **matthew1** » 22 Mar 2026, 13:26

If I have a 200 Watt electric heater and a PC that I can make run at 200W, they will both heat a room at the same rate, correct?

Post by **abscate** » 22 Mar 2026, 14:54

matthew1 wrote: 22 Mar 2026, 13:26 If I have a 200 Watt electric heater and a PC that I can make run at 200W, they will both heat a room at the same rate, correct?

High school exam question - yes, 200 watts power is 200 joules of energy every second being put into the room.

College answer - yes, if the heat of the computer mostly goes out the fan as air flow, which I think is true

Graduate answer - if the computer is near a wall or furniture or something, you might get local heating of some part of the room so the air temperature might not go up as much as a space heater. Also if the heating is sunk into the case, you would get a hot computer and cooler air.

Postdoc - I don’t care l have to get this experiment done

Assistant professor - If I can’t publish this in Science it will have to wait

Professor - I’ll ask my group

Follow up question..if you use a chiller to get the heat out of the computer, does the room run cooler, balanced out to no heat flow , or hotter than above?

Hint - feel around the back of your fridge.

Post by **volvolugnut** » 22 Mar 2026, 14:58

I will say PDC (pretty dang close). I think a PC will have little electric load other than heat output. Maybe some power to turn the fan.
I remember times when I did not have AC in a motel room. The tube type TV would really heat the room.
Also, an engineering office with many computers will need AC nearly year round.

Addendum: I was typing while abscate posted his reply.

volvolugnut

Post by **matthew1** » 22 Mar 2026, 15:21

I figured as much... that they would be equal even if there is "cooling" (which I do have for my PC) but IIRC electrical work is work, as an absolute. Conservation of... mass? Mass is energy, so conservation of energy principle?

The cooling is a red herring because we don't get anything for free?

Steve your answer was very humorous!

In 1980 I had one of the best school days of my young life. Our teacher had us divide into three groups. The first group put an icecube in a glass of 80 degree F water and time how long it took for the ice cube to melt. The second group did the same with 60 degree F water. The third group was my group and ours was 40 degree F water.

My group's ice cube didn't melt for something like 3 hours, and we got to miss boring classes after that to stare at the ice cube. It was way longer than the class thought it would be because the starting temps were not linear as the starting temp approached freezing. I don't know if this is related to my Watts question, but it triggered the memory.

Post by **matthew1** » 22 Mar 2026, 15:42

I need to get my Kill-A-Watt out and see what my PC actually draws. I think the power supply is good for 500W or so, but it never draws that much.

Post by **volvolugnut** » 22 Mar 2026, 17:54

Consider the incandescent light bulb. Memory says it is only about 1-2 percent efficient in producing light from power input. That makes it 98 to 99 percent efficient at producing heat.
Good old internal combustion engines are at best about 30 percent good at producing power from fuel so they produce about 70 percent waste heat. However, if you are in cold climate, that waste heat does a great job of warming the cabin and defrosting the windows.
Memory says a vehicle that got 100 MPG would have very little waste heat available to do much cabin warming.
volvolugnut

Post by **abscate** » 22 Mar 2026, 23:06

Gasoline has about 36 Kw hr energy per gallon, so a gas car needs uses 2 kW hr per mile , rounding a bit

a good EV gets 4 Miles per KW hr

only about 30% of that 2 kwhr of the gas car gets used for motion, so there is plenty left for heating. 1 kW hr per mile is a lot of heat.

One space heater will cook a car quickly. If used as a heat pump, 1 kW hr heat pump will move 3 kWhr of heat, even better.