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How can I figure actual power consumption for my kiln, without buying a wattmeter? Answered

I'm working on some fused glass projects for sale, and I'm trying to figure my kiln's electrical consumption into the price of the items as accurately as possible. I can easily figure the max draw of the kiln, but it's not running full tilt throughout the whole fusing cycle. In fact, through much of the cooldown phases, it hardly comes on at all. I don't want to grossly overestimate and gouge the customers, but I also dont want to underestimate and lose money on the sales. I also don't want to buy a 220v wattmeter that I'll never use again. I don't need super-precise measurements, just reasonably accurate ones.
Is there a feasible alternative to a wattmeter for this application?



Best Answer 8 years ago

Even if you grossly overestimate the electrical cost it's not going to be much.  Figure full time usage and and half it.

Go on to the next part of the project, you've got much more important things to do.

When selling art that you've done you CAN'T gouge the customer.  It's worth what ever they will pay.  The value of the art bears little or no relation to the cost of the materials.  The value is in it's apeal to the customer.  And that comes from your talent and hard work.  You will always undervalue that.

Now these fused glass project you're making wouldn't happen to be customized reed switches would they?

Too true.  I just hadn't considered the actual kwh costs yet. I was focusing first on measuring energy consumption, without taking into account whether the actual costs would be significant enough to even worry much about. Considering that I will be fusing several pieces at once, the actual firing cost works out to less than a buck per piece. Shoulda done that math first....

And since you asked, the project is making open-weave baskets and other similar container-thingys out of recycled wine and beer bottles. I will be sure to work in a reed switch as soon as the opportunity arises, though. :-p

for an electric kiln the calculation is as follows


for a 220 V kiln running at 30 Amps = 6,600 watts (6.6Kv)
 one hour at this power = 6.6Kwh 

i pay .21 per Kwh whish comes to $1.38 per hour.

to cone 10 takes 7 hours at full honk= $9.98 per glaze fire.

for the other levels, (low fire glaze and bisque) I refer to the power draw in my kiln manual.

some kils operate on a ccycling on/off (electronic control) cycle, some use a constant on method at lower power levels (manual and Kiln Sitter kilns)  these are always on, but low has every 1 of every 3 elements on, and meduim has every other lelement on ) reducing the total power usage.

best bet, fire the kin and cjeck your electric meter to see how much poer per hour you are using and oposed to when it's not on...

how about this for a rough estimate:
the heaters are either 100% on or 100% off, use a stop watch and measure the on time (like when the heater element is on, im assuming it has a fairly large relay that you can just hear).  take that time, and your kiln is using ~the max wattage rating for that long

I had considered something like this, but the problem is that the fusing cycle runs for about 22 hours on average, with the relay kicking on and off at irregular intervals. Doing this would work very well, but it requires a level of dedication that my lazy 42-year-old carcass just won't support. ;-p

What you really need is the total "on" time for a full treatment.  If you run a wire off ONE of the switched leads to the heating element (tie it in at the relay) to a cheap electromechanical lamp timer and another from the timer to neutral (white wire) then you'll get 110 v only when the element is on.  Set the timer to midnight and start the kiln.  The timer will only run when the element is on.  When everything's done, see what time the timer thinks it is.  If it's at 10:00 AM, your element has been on for 10 hours out of the cycle. 
Then you can multiply that by the KW rating of the kiln and get KW-hrs.

I'd cut up a cheap extension cord and use alligator clips to make the temporary connections since the timer draws so little current -- just unplug everything first!  And keep the boy out of there.

This I like. It has exactly the right mix of "bodged-together" and "potentially lethal" to be really appealing to me. ;-p

Yeah, cheap & dangerous tend to go hand-in-hand.  If you keep the plug-end of the extension cord intact you can at least plug it into a wall outlet to get the neutral wire.  Clip the hot wire of the x-cord near the plug and seal the stub well.  That would make it safer.  Unzip the cord and put the alligator clip on the free end of the hot wire.  Then the only exposed connection is the alligator clip to the relay.  The timer would just plug into the xcord outlet.  I'd probe the wall outlet first to make sure the hot and neutral are where they're supposed to be.

Did you see this?  It showed up on the sidebar:

I want to see how you make baskets out of bottles when you get that going.

I did indeed. That's precisely why I bought that cheap tile saw from Chris the other day. Once I get the project going, I'll be making an Instructable as I go, so all will eventually be revealed.
Or just come on by the studio. I cleaned it up and everything. And I have beer.

Sounds like you can get a tolerably close estimate by just taking the fusing time and multiplying that by max draw...?

Or just look at your electrical bill in months when you're working vs. months when you aren't (allowing for other differences in use due to season and so on).

I agree with the others that the customers will tell you if you're overcharging by not buying... and that if you want to not lose money you need to look at ALL the costs of running the business. Which includes the value of your time, and the time and cost for pieces which fail and/or aren't marketable.

Of course you get some value from simply having an excuse to play with your hobby. So it may not have to cover its real costs. Mine doesn't, though it produces income occasionally, and I'm OK with that.

Yeah, I don't really do any of my stuff for money, but it's nice when they at least pay for themselves occasionally. Makes RavingWife less likely to kill me in my sleep....

Problem with that is that you bring down the price for people trying to make a living at the same thing.  Make people pay what it's worth, or give it away.  Otherwise you (and your fellow crafters) will never be accepted for what you are worth.

I saw a 3' long polymer clay dragon with a conservative 40 hours of work put into it, with documentation along the way, sell for $400. No way the artist paid for costs, but someone tried to use that as a case for 'you can make money with your art'!!!!

Most of my stuff I do give away, and I very rarely make anything that someone else is already making in the same market, so competition with other artists is not generally an issue. Plus, when I do sell things I always give a lot of thought to fair market value. I seriously doubt I'd be undercutting anyone, unless their prices were grossly overinflated to begin with.
Just out of curiosity, what was the original asking price on the dragon? That's a boatload of polymer clay....

E-bay auction, but only the outside was polymer clay-still a lot invested in it.

If you have the "instantaneous" load, ie, power, then just buy a user-resettable hour meter. Connect it so that it's on only when the kiln is running.

An hour meter is a nice thing to have on a large piece of industrial equipment anyway, as it tells you the working age of the device for maintenance purposes.

If I had any idea how many hours were on the kiln when I got it, that would be a great idea. As it is, I'm just planning on using it until it dies and then giving it a total rebuild. Maybe after that.... I think for price purposes, I'm just gonna take a WAG at it and call it good.

Work out your "current" (sorry) domestic baseline energy consumption (read the meter daily for a week), take a mean. Do the same while you are running the kiln. Subtract.


I probably will do this, but I expect it'll take more than a week to get a really good answer.
Our energy use fluctuates quite a bit from week to week even without the kiln, just based on things like laundry and dishwasher use, whether we cook at home or eat out, how much the central heat/air gets used, whether we're running the pool pump or not, etc, etc. Given the seasonal impacts, it could take months to collect a valid sample.

I guess because patience is a virtue, and no one has ever accused me of being virtuous... :-)

You should look at pricing from the perspective of what you need and what people are prepared to pay you.
Calculate total overheads on total energy, tooling, equipment, property, administration (& anything else) to arrive at $ per quarter. Ensure your margin on finished goods covers this. Something like materials + labour + %margin, round to the nearest nice-looking value.


You're right. I'm overthinking this. It's what happens when a Business Systems Analyst goes into art....

It might be worth doing it as a one-off exercise. If you price your current stock, put the values into a table, e.g. size/weight in columns & type/design in rows, you could draw up a standard price list extrapolating the empty boxes. Future stuff you say "it's one of them, at that size - that much $"?


Oh yeah, once I figure out a general price structure one time, that's it. Close enough is close enough.

.  Tools: Voltmeter, ammeter, stopwatch/clock.

.  Procedure:
.  Take V and I readings every X seconds|minutes|hours.
.  Multiply V times I to get VA's. Since you are using a resistive load, VA = W.
.  Compute an average.

Turn everything off from the breaker. Go outside and read the meter. Now only turn back on only where the kiln is plugged up to. Turn on the kiln. Place the paces of art in the kiln. Wait until it’s finished being fired. Turn off the kiln.  Go back out side read the meter. Then minus the start meter reading from the ending meter reading. Then go to your electric company ask how much they are charging per watt or look on your bill. Times the ($ per watt) by the total of the used energy( found above). Then you should have your amount for kiln firing but also you can dividing that by the amount of paces in the kiln. To figure out the price per pace of art.


Totally workable, except for the whole going without electricity for 22 hours thing. If a weekend rolls around when RavingWife and RavingChild are out of town, I'll give it a crack, though. I think my refrigerator will stay cold for that long....


8 years ago

id suggest using a scribble chip,they work around 1000degrees and monitor closley the consumpsion of variable heat to profit expenditures down to a decimal place of arround a tenth division three oe over six.they are widely available in red or blue but i hear plans are well in the pipeline to produce a carbon coated polyimbular free green one..although not cheap your long term profit margin can only be benificial in your favour...............failing that try a small animal in a pyrex jug...youl know when it gets too hot

Hmm... I don't have any small animals. Can I use one of the neighbor's kids?