View Full Version : Electrical Usage of Individual Tool

Dan Stuewe
11-03-2006, 8:22 PM
Recently my wife bought a kiln for her jewelry/glass business. It is pretty hefty and required a few thousand $$ just to upgrade our electrical service (yes, I did throw in a couple of 220V boxes on "my" side of the garage). Anyway we've received two electric bills since the kiln has been up and running and they have been huge! (anything over $70 is huge here in coastal Orange County, and these two have been $120-$190) This last one showed almost a doubling in electricity usage compared to the last two years. In the past (last year) we wrote off as business expense a percentage of our utilitites based on the percentage of our home's square footage that is used for the business. That seems fair enough when you concider lights, small tools and the computer. But based on the huge load this one tool uses I'm wondering if there is a way to track its electricity usage for tax purposes. I need to call our accoutant, but I thought I would throw this out for discussion here as well.

(BTW, we have the power requirements/specs and we could keep track of the pre-programed timing, but I'm sure the heating coils go on and off during the heating cycles, so I don't know how accurate it would be to simply multiply these two numbers to get kWhrs.)


Lloyd Frisbee
11-03-2006, 8:43 PM
I have seen devices that measure electrical usage. Here is one. www.theenergydetective.com

Just do a google search and you should find something.

Joe Pelonio
11-03-2006, 8:54 PM
There are such devices but I have never seen one that works on a 220 device like that kiln. If you can't find one try this:

I used to work in Water conservation, not electrical, but this method should work as well. Shut off all electrical lights and devices in the house.
Go out and read the electric meter. Run the kiln for 5 minutes. Shut it down and read the meter again. The difference in readings X 12 = the amount it uses in one hour.

Using the information with your bill on rates figure out how much that translates to in dollars/cents. This may change by season on your area.
Use a simple timer whenever running the kiln and record the time. Do a spreadsheet to convert to cost and keep the spreadsheet in the computer and hardcopy to document in case of future IRS audit.

Ian Abraham
11-03-2006, 9:41 PM
Yes, problem with measuring a kiln is that it will draw it's peak power as it's warming up. After that the thermostat will kick in and it might only use 50% power as the heaters cycle on and off.
It's power requirements should be stamped on the unit, probably with the serial number. Volts x amps gives you the watts. 1000 watts for 1 hour = 1 kw/h = 1 unit.
Will be hard to get power use exactly right without a fancy meter, but you can at least estimate what it's using, probably well enough to claim on anyway. See if your numbers come out approx the same as the power bill increase, that would be a good indication.

And yes, something like that could use as much power as the rest of yourr house combined :o


Bill Turpin
11-03-2006, 10:04 PM
If the kiln has a "ON" light that cycles with elements, watch the use pattern during different portions of the profile. Figure a % on-time at each step, do a little math. This multiplied by the KW will give you KWH. Example: 10KW(element rating) x 50% (on-time) x 24 hours(per run) x 10 cents/KWH (my rate) = $12.00 per run. Put in your KWH rate, etc and you have your cost.

Bill in WNC mountains

Perry Holbrook
11-04-2006, 8:59 AM
Dan, as an ex-energy management engineer, most of the above methods make logical sense. However, in the case of a glass kiln, they do not apply. I have 2 kilns in the glass studio that are probably as large or larger than your wife's and have tested their usage and found that in a normal firing schedule they cost about $4.00 - 5.00 per firing with an electric rate of $ .095 per kwh.

Now for the reason the locical approach of sample testing doesn't work. A glass firing schedule is usually in 8 to 10 stages. An example would be : 500 dph (degrees per hour) to 875 F hold for 30 minutes; 300 dph to 1100 hold 45 min; 180 dph to 1375 hold 60 min; 500 dph to 1450 hold 50 min; off til cools to 1050; 75 dph to 1015 hold 45 min; 70 dph to 875 hold 5 min; 120 dph to 300; off.

And these schedules change depending on what you are firing. Because of the varing firing rates and holding times, the sample test is not accurate. I could talk about this much longer than you would be interested in hearing me.

The bottom line is that the only way to know for sure is to equipt the kiln with current transformers and a recording meter, much to expensive. Another way is to break into the control panel and wire an electric clock in series with the coil wiring on the element relay. When the relay fires, the clock will advance a few seconds at a time. At the end of the firing the total time on the clock is the total time the relays fired. Then do the math to determine kwh usage and cost.

People who have went to the trouble to do this have discovered that their kilns are firing about 15% - 20% of the total firing cycle. You could plug that into the logical approach an see if it makes any sense in your case.

Hope this helps. Perry

Dan Stuewe
11-04-2006, 11:17 AM
Thanks everyone for the great responses. It will never cease to amaze me at the diversity of talent and knowledge of my friends on this site!

I'll try to talk to our accountant next week to see what would be a fair approach to take with the IRS. (I don't know if this is the best business practice, but for now pretty much all the income from the business goes back to the business so I'll just transfer some $$ from the business account to the personal account when I pay the bill.)

One other problem is that we have several rates depending on usage: 1 baseline, 2 over baseline, 3 a bit more over baseline, 4 a lot more over baseline etc. So one rate for any usage is more difficult to come up with. On the other hand, I'm sure the IRS would give us the benifit of the doubt if they every audited us, right? :rolleyes:

And these schedules change depending on what you are firing. Because of the varing firing rates and holding times, the sample test is not accurate. I could talk about this much longer than you would be interested in hearing me.

Perry, it might be more than I'm interested in, but I'm sure my wife would love to talk to you. BTW, she is working with fussed glass. This is her kiln:


Thanks again everyone.

Perry Holbrook
11-04-2006, 2:11 PM
Dan, yeah my fusing kilns are larger than that one, but at the moment I don't remember their amp draw.

As far as the rates are concerned, I know things are a lot different in your part of the world, but it sounds like your rates are somewhat similiar to the industrial rates I dealt with in my past life. If you can get your hands on the actual rate structure you can do the math if you want the exercise.

What you have to do first is to determine or estimate the total KHW (and added KW if their is a demand charge) used by the kiln in the billing cycle. Then subtract those numbers from your overall totals on the bill.

Now take your rate schedule and do the math on your overall bill to see if your numbers jive with theirs. If it doesn't keep working on the math until you have the rate formulas figured out. ( Don't mean to question your math skills, its just that some of those rates can be difficult to correctly understand). Then do the math using the same schedule but this time with the kiln numbers removed. Compare the difference and you will have the actual cost of operating the kiln.

Again, probably more than you wanted to know, but thought I would share.


Jon Fowler
11-19-2006, 7:28 PM
I would recommend you contact your power company and request an energy audit. They will have the tools etc.. to help you determine how much the kiln and other tools are costing you to operate. I work for our local power company and we have one individual dedicated to doing home and business energy audits to assist customers.

Frank Hagan
11-19-2006, 11:25 PM
Your SoCalEdison bill has the KWH you used last year, and if the kiln is the only thing that you have added, then the average (over time) of your usage over the average last year is what the kiln is costing you.

No need to spend a lot on meters, etc. If you don't have A/C then you don't even have to worry about different temps in the summer throwing off the average.

Our commercial Edison rates at work range up to about .20 a KWh for usage over the baseline (something like that ... I'll have to look again). Our 5,000 sq. foot office in Simi Valley will run over $5,000 to run the A/C in August at those rates, while the electric bill is much lower in the winter. You might look at your bill and see if you have the much higher rate kicking in because you are over the baseline threshold.

Frank Chaffee
11-20-2006, 1:54 PM
Check with your power providerů they may very well have a device available that you can use free of charge for this purpose.

Frank Chaffee