Heater Duration

bugs

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7 Sep 2007
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So, if you were going to use the PFK tank running cost calculator and therefore need to specify the number of hours the heater was running, what would you estimate based on a tank in a centrally heated house?
 

bugs

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7 Sep 2007
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Yeah, I appreciate there's all manner of variables BUT, if you had to hazard a guess... I'm figuring I'd take the average of the guesses to flatten the variables. Not particularly scientific but good enough.
 

Egmel

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Guildford, Surrey, UK
If you contact your electricity supplier they should be able to send you a plug in electricity meter free of charge. Then if you have everything plugged into one extension lead you can use this to measure how much your tank costs you to run for a day/week/month etc. The meter is about the same size as a digital timer and you tell it how much your units of electricity cost and it does the rest :)
 

bugs

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Not E.ON is seems - not unless you sign up to a contract...

So nobody prepared to even hazard a guess at how long their heater runs for?
 

bugs

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I'm hard pressed to find my heater switched on. I know it's been warm recently but my house stays reasonably cool and we never heat it above 19c. The lights must be slowing the heat loss. I recorded the heater light on two separate occasions for 1 hour each and the light did not come on once!
 

bugs

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7 Sep 2007
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This evening I recorded the heater lamp for 1 hour (having turned OFF the heater cable...).

Known:
Heater wattage: 150w.
Tank capacity: 75 litres.
Room temp (start): 19c
Room temp (end): 20c

Heater on periods:
1. 2mins, 50secs
2. 2mins, 35secs
3. 2mins, 29secs

So, based on these variables, the heater would run for 3.16 hours per day. Total cost: £20 to £38 per annum (secondary rate / primary rate) running cost.

So... working on a principle of 2 watts heating per litre, a 350 litre tank would dictate a 700 watt heater to apply these findings. Total cost: £94 to £181 per annum running cost.

Anyone want to buy a second hand 350 litre tank?
 

Egmel

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Joined
28 Mar 2008
Messages
724
Location
Guildford, Surrey, UK
bugs said:
This evening I recorded the heater lamp for 1 hour (having turned OFF the heater cable...).

Known:
Heater wattage: 150w.
Tank capacity: 75 litres.
Room temp (start): 19c
Room temp (end): 20c

Heater on periods:
1. 2mins, 50secs
2. 2mins, 35secs
3. 2mins, 29secs

So, based on these variables, the heater would run for 3.16 hours per day. Total cost: £20 to £38 per annum (secondary rate / primary rate) running cost.

So... working on a principle of 2 watts heating per litre, a 350 litre tank would dictate a 700 watt heater to apply these findings. Total cost: £94 to £181 per annum running cost.

Anyone want to buy a second hand 350 litre tank?

If only it were that simple!

Were these test done during lights on or lights off?
The temp gradient between the water and the air is ~6C in these tests how does it compare for greater or lesser gradients? (Different times of the year)
What about the surface area to volume ratio, this will change as tank size changes and therefore the heat lost to the surroundings per litre will differ between tank sizes and dimensions.

I think the only way to know for sure how much energy your heater uses is to get an energy monitor and measure it. You can plot weekly consumption on a graph and then see how it changes throughout the year. But remember the results you get will be specific to your tank/room set up and will probably be completely different from someone else's results. (Unless of course you have identical set-ups in similar rooms)
 

bugs

Member
Joined
7 Sep 2007
Messages
365
Egmel said:
bugs said:
This evening I recorded the heater lamp for 1 hour (having turned OFF the heater cable...).

Known:
Heater wattage: 150w.
Tank capacity: 75 litres.
Room temp (start): 19c
Room temp (end): 20c

Heater on periods:
1. 2mins, 50secs
2. 2mins, 35secs
3. 2mins, 29secs

So, based on these variables, the heater would run for 3.16 hours per day. Total cost: £20 to £38 per annum (secondary rate / primary rate) running cost.

So... working on a principle of 2 watts heating per litre, a 350 litre tank would dictate a 700 watt heater to apply these findings. Total cost: £94 to £181 per annum running cost.

Anyone want to buy a second hand 350 litre tank?

If only it were that simple!

Were these test done during lights on or lights off?
The temp gradient between the water and the air is ~6C in these tests how does it compare for greater or lesser gradients? (Different times of the year)
What about the surface area to volume ratio, this will change as tank size changes and therefore the heat lost to the surroundings per litre will differ between tank sizes and dimensions.

I think the only way to know for sure how much energy your heater uses is to get an energy monitor and measure it. You can plot weekly consumption on a graph and then see how it changes throughout the year. But remember the results you get will be specific to your tank/room set up and will probably be completely different from someone else's results. (Unless of course you have identical set-ups in similar rooms)

Sometimes there is beauty in simplicity, even if it is at the expense of some accuracy. Essentially I have a good enough answer to the question I originally posed. Of course, anyone wanting to take a more scientific approach should take note of Egmel's comments.
 
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