Calculating heater energy consumption

[VinsonMassif]

I am curious as to how much energy a heater in a tank actually uses because the heater is not on all the time.

And one would assume that a higher wattage a heater is rated at then it would heat the water quicker, and therefore use less electricity to maintain the tank at a specific temperature. Is this true?

The energy calculators online seem to assume the heater is on every minute of every hour, which is not the case. And a lot seem to work on a basis that you only use the heater 6 months of the year.

My 300W heaters seem to come on for 3 minutes with a 5-6 minute gap at the moment. Sure it would be more frequent during the frosty nights.

Has anyone calculated the energy used to heat a specific tank volume and maintain it at a certain temperature?

For instance: a 300W heater in a 200L tank heating the water to 25*C, with the room temp at 15*C.

[Ira]

And one would assume that a higher wattage a heater is rated at then it would heat the water quicker, and therefore use less electricity to maintain the tank at a specific temperature. Is this true?

No. The heater will only replace exactly the amount of heat lost(Unless it's too small to maintain the temperature)

My 300W heaters seem to come on for 3 minutes with a 5-6 minute gap at the moment. Sure it would be more frequent during the frosty nights.

If that's an accurate average then you'd be using an average of 100 watts of power or 2.4 kw/hr per day. Roughly $.50/day.

Has anyone calculated the energy used to heat a specific tank volume and maintain it at a certain temperature?

For instance: a 300W heater in a 200L tank heating the water to 25*C, with the room temp at 15*C.

Energy required to heat 200L of water to 25c is straightforward math assuming a starting temp of 15C and assuming no losses of heat during the process. Heater wattage is irrelevant.

It takes 4.2 joules to heat 1 gram of water 1 degree c.

So you're heating 200,000 grams 10 degrees. So, 200,000*10*4.2=8,400,000 joules.

One joule is 1 watt second or 3,600,000 joules per kilowatt hour. So 8,400,000/3,600,000= 2.3 kw hours to heat 200L costing $.40-$.50

Only effect in a perfect situation the wattage of the heater would have is the length of time it would take, in this case is that it would take roughly 7.6 hours.

Calculating mathematically the heat loss of the tank though is more complex. You'd need the outside air temp, glass thickness, glass area, adjustments for heat lost through the base, to air through the lid, etc.

Might be easier to get a watt meter throw it on the heater for a week. (Something like $12 at the warehouse) Then you'll know the power usage and can calculate the average rate of loss. Watts of electricity used=watts of heat lost (Resistive heaters are 100% efficient)

[VinsonMassif]

Awesome thanks for that explanation Ira.

[Aquatopia]

And its worth remembering that during the cold winter months, you can reduce cost by putting insulation around the tank - or if that is not aesthetically pleasing you can at least put a cover over it at night when the ambient temperature is at its lowest.

[VinsonMassif]

Yeah atm I have 20mm poly around the sides, back and base of each tank.

I am getting some to cover the front and top at nights.

[Aquatopia]

its a good call should make a difference, esp for those with MTS (assuming the poly doesnt cost much to get hold of )

[ryanjury]

Has anyone figured out an ingenious way of attaching the poly to the tank that wont leave residue like tape etc and wont leave huge air gaps meaning it doesn't insulate very well?

[VinsonMassif]

I used clear tape in places that are not obvious.

Residue comes off easy with meths.

[phoenix44]

push the poly against the tank, and then push the tank against the wall.

so you then have wall, poly, tank - all tightly packed.

[supasi]

I just taped mine on.

As Vinsson said, comes off easy with meths.

[David R]

Go to Bunnings and buy a $20 power meter so you can measure the kWh the heater [or anything] uses.

[phoenix44]

I find PFK Uk's calculators really useful. for example based on my tank, I use an average of $20 a month in electricity on my 4ft tank, with all that lighting, heating and filtration etc. it gives you a breakdown of what each component uses.

have a play with their other calculators too if you like.

This one is for the electricity of a tank, you just have to input what it costs you per kWH. eg in my case it is 20.075 cents = $0.20075

http://www.practicalfishkeeping.co.uk/p ... _costs.php

[VinsonMassif]

Cheers for that.

Our power went from 23.92 to 26.74c kwh this last account.

It costs me $27 for my 4' tank atm.