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Workshop Heating

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Donald Mitchell25/11/2017 13:36:10
90 forum posts
3 photos

Hi all, I have a wooden workshop down the garden path, I expect this describes a great many of our amateur workshops. When I built the shed (which is 5m x 3m) I spent heavily on wall, floor and ceiling insulation, double glazed windows and a UPVC double glazed door. The shed is normally no great problem to heat with a 1Kw electric convector and I do not suffer with condensation. During the colder months of the year (in Scotland) I leave the heater turned on 24/7 plugged into a simple thermostatic switch (not a timer) which I leave set to 12deg C. When I go into the shed to work it is then a simple matter to overide the thermostatic switch and heat up the shed to about 17deg or so which I find is adequate if I am hard at work.

Every time I enter the workshop I notice the internal temp is as I have set on the thermostat, ie. 12deg and I also notice that about 8 out of 10 times I go in, the convector heater is cool to the touch; suggesting to me that the heater does not spend too much of its time switched on, which is good. It would be interesting to know in fact how often the heater is on and for how long it is on when I am not there.

I cannot count the on/off times by simply leaving it at 12deg when I am there, because a/ its too cold at 12deg and b/ I'm sure my own body heat (I'm a hard worker) would slightly raise the shed temp and c/ machine motors will create heat also.

Please don't any wise person suggest that I sit and don't move for several hours and don't switch on any machines and count the on and off's.

Here is the question:- Does anyone know of any sort of smart leccy meter I could plug into the same circuit which would record the on/off times and durations overnight for example?

Happy Christmas to all.

Donald from Bonnie Freezing Scotland.

Clive Brown 125/11/2017 13:53:27
481 forum posts
18 photos

Google something like power meter plug. Maplin and Amazon are possible suppliers. They will give total kWh usage, but not the number of cycles

Edited By Clive Brown 1 on 25/11/2017 13:58:49

Robbo25/11/2017 14:03:07
1504 forum posts
142 photos

Back in the olden days before all this electronic gadgetry, I wired up an electric timer switch so that when the heater came on then so did the clock on the switch. Likewise when the heater went off the timer switch stopped.

Set the clock to "zero" and checked within 24 hours the elapsed time on the switch compared to the real elapsed time.

This was to check how long the heater in a greenhouse was on in any 24 hour period.

Emgee25/11/2017 14:05:58
1650 forum posts
224 photos

Hi Donald

You could connect a 230v hours run meter live input to the live output from the thermostst and neutral, check each day at the same time to read and record the hours ON time for a complete record.

You could use any 230v time clock in place of the hours run meter, just remember what time it was set to when connected, best to reset time daily.


Edited By Emgee on 25/11/2017 18:39:42

Donald Mitchell25/11/2017 14:07:03
90 forum posts
3 photos

Yes thank you, I have already found various plug in meters via Google, Amazon & Maplin etc which will record the Kwh used and the total time on over a period of time but I can't seem to find anything which will also record the individual on periods on the time o' clock scale.


Brian Wood25/11/2017 14:07:19
2244 forum posts
37 photos

Hello Donald,

What I think you need is an elapsed hour meter that you can couple into the heating circuit in parallel so that it counts the time the heater is actually powered up.

Radio Spares sell very neat little versions made by Grasslin in 240 volt rating that will record 10,000 hrs, together with 1/10ths and 1/100ths that would do the job admirably. I have one in my workshop doing the same job as you describe and I have used them to record running time on oil boilers. They are non resettable




Edited By Brian Wood on 25/11/2017 14:10:02

Neil Wyatt25/11/2017 14:10:00
18133 forum posts
713 photos
77 articles

Your approach for getting a rough impression of how long its spends switched on is actually a reasonable way to get a more accurate result. You just need to be more methodical.

Keep a count of whether or not the heater is switched on the next 20 times you go in the workshop.

Multiply by five (because that's 100/20) and you will have a reasonable estimate of the percentage of time it is switched on.

More samples will give a more accurate result; bear in mind it will probably spend more time on in the cold of the night/early morning.


Muzzer25/11/2017 14:35:48
2904 forum posts
448 photos

I would expect to have to pay more for an energy meter that actually logs or reports the usage against time. I've got one of those Maplin meters that tells you the cumulative energy used - and the cost if you tell it the cost per kWh. Pretty good for the price.

These days it would probably be a "smart" switch that you need to use. These allow remote control of loads by a smart phone or PC and some report back actual electrical load. I'm not expert in these matters but there seem to be a few around these days such as this from TPLink. Seems pretty good for £25 (currently reduced from £35) but whether or not this can be justified is another matter.


Mike Poole25/11/2017 14:44:38
2699 forum posts
64 photos

Sounds like a task for an Arduino or Raspberry pi.just wire a relay to energise when the heater is on and log it with the device of your choice.


Journeyman25/11/2017 14:48:38
810 forum posts
142 photos

You could use one of these to monitor the temperature:-


There are apps for mobile phones that could act as a slightly more modern version of the thermograph or possibly a program for the workshop computer with a suitable thermistor plugged in.


not done it yet25/11/2017 14:54:04
4877 forum posts
18 photos

The on/off cycles will depend on a few factors whereas the energy used will depend on the insulation level and how draught-proof the workshop is. Outside temperature and wind/rain will also be uncontrolled variables.

If the heater is of small wattage, it might stay on almost all night long if necessary, whereas a high wattage heater might be on and off like a yo-yo goes up and down! Position of the heater and air circulation might also be a factors to consider.

So energy used is the really useful measurement, unless the heater is raising the temperature far in excess of the thermostat setting.

Lidls sells energy monitors occasionally. About a fiver a go, I would guess.

Getting it warm (machines and other contents), if the temp drops below the target will take more heat than maintaining it. I might suggest a dessicant type dehumidifier would help in your situation - keeping thevhumidity low while warming the shop. That is what I currently do, but the dehumidifier is simply on a time clock (I live much further south than you).

While a simple thermostat is probably perfectly satisfactory, there are other alternatives like proportional controllers (even PID if you want to go OTT!) as well as dimming types which simply never turn the heater off but reduce its energy consumption to close to zero or increase full on to maintain the prevailing conditions.

Mark Rand25/11/2017 15:08:01
918 forum posts
6 photos

If you're up to soldering a resistor and a three terminal device to the pins of a Rasberry Pi, then copying a few lines of code, you can do this sort of thing:-



Edited By Mark Rand on 25/11/2017 15:09:33

Donald Mitchell25/11/2017 15:09:32
90 forum posts
3 photos

Lots of good ideas coming out of this question which I'm sure are applicable and interesting to most of us.

Looks like I may just have to settle for Kwh total used, measured at the same time every day or morning, which I can get by just plugging in an old-fashioned mains powered clock in parallel with the heater. It would be nice to be able to plot the times it is on but maybe not easily accomplished without expensive kit and/or a computer in the workshop.

Speedy Builder525/11/2017 15:12:24
2079 forum posts
145 photos

If you want to go a bit more Hi tech, you could use a power fail app on an Android or similar mobile phone. Take a live feed from from the switched side of the thermostat as the live feed for the charger of your mobile. Then when the power is switched via the thermostat, the power fail app on the mobile will send a text message to a second phone. (I don't know if it could send a text to itself ??). I actually use a power fail app to tell me if the freezer power has failed whilst I am on holiday etc. But I think the old time clock is a good idea.

Clive Brown 125/11/2017 15:18:52
481 forum posts
18 photos

USB temperature data loggers seem to be available fairly cheaply. Leave one plugged into a PC near the heater and download temperature history to say Excel. The temperature cycles should be easily seen and counted, but it's all getting a bit OTT perhaps.

Donald Mitchell25/11/2017 15:22:17
90 forum posts
3 photos

Don't have a PC in workshop, only a hammer. Thanks anyway.

V8Eng25/11/2017 15:42:36
1463 forum posts
28 photos

Clive's idea is very good. Something like this (self powered) would probly work, take it away and download iindoors via USB.

i used one for all sorts of temp monitoring.


Many other suppliers as well.

Edited By V8Eng on 25/11/2017 15:46:10

Brian Sweeting25/11/2017 16:13:56
437 forum posts
1 photos

As V8eng has suggested but a bit cheaper is this dual sensor data logger. You could then record inside and outside shed temperatures.

Edited By Brian Sweeting on 25/11/2017 16:14:43

martin perman25/11/2017 16:28:10
1857 forum posts
78 photos

Slightly off track but having just read about the USB temperature trackers in this thread, I've ordered one to prove to my wife that our house doesn't turn into a fridge when the heating switches off smiley

They are not expensive and only need to be connected to the computer when downloading data.


Martin P

Edited By martin perman on 25/11/2017 16:29:55

V8Eng25/11/2017 17:00:17
1463 forum posts
28 photos
Posted by Brian Sweeting on 25/11/2017 16:13:56:

As V8eng has suggested but a bit cheaper is this dual sensor data logger. You could then record inside and outside shed temperatures.


Edited By Brian Sweeting on 25/11/2017 16:14:43

That looks to be just what the wife is looking for to use at the greenhouse, thanks Brian.

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