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Glassware Ovens Don’t Need to be on 24/7/365

If you work in a chemistry laboratory, particular a lab that does synthesis, odds are you have a glassware drying oven. These ovens are usually set somewhere between 100-150 °C and are used to remove adsorbed water from glassware. Water, while necessary for life, has a nasty habit of being rather bad for much synthetic chemistry.

If you haven’t ever seen water being driven off seemingly dry glassware using fire, I recommend trying it yourself – or watching this YouTube video:

Fortunately, you do not need fire to dry glassware (though let’s be real: chemists like fire). It has long been recognized that ovens are perfectly adequate for drying glassware:

“The application of (oven) heat appears to be a highly effective method and is neither costly nor time consuming, i.e., makes glassware available for repeated use in the minimum amount of time.”

Drying volumetric glassware, Bernard M. Mitzner, J. Chem. Educ. 1956, 33, 12, 609

(apparently chemists have been arguing about whether volumetric glassware can be dried in ovens for at least 70 years without modifying the volume – a newer study rather convincingly showed that volumetric glassware tolerates heat just fine – but I digress)

Enter the humble laboratory drying oven.

it wouldn’t be complete with old signs and post-it notes

Now here’s the problem from a sustainability perspective. Lab ovens typically are plugged in, turned on…and then left on…24 hours a day, 7 days a week, 365 (+1 day occasionally), year, after year, after year…decade after decade…

Intuitively we would suspect this constant usage consumes a ton of electricity – if you pay your own electric bill, you definitely wouldn’t leave your oven at home on 24/7. So, we at SMC pulled out an energy meter and started measuring.

oven / temperatureoven capacity (L)kWh / day
Newer convection oven at 120 °C53 L3.4 kWh
Older lab oven at 145 °C (poor heat control on this older oven)32 L ish7.2 kWh

You can see that there is big discrepancy between newer vs. older ovens, and a difference between newer and older ovens. That makes sense. Newer ovens are probably better insulated. When considering whether we could put our ovens on timers to shut them off at night and on the weekend, someone asked:

How much energy do ovens consume during warm up? Would start up energy cost that negate any benefit of using a timer?

a scientist in smc

Well, these guys have addressed a similar question for lightbulbs…

Mythbusters, by Max Goldberg, CC BY 2.0

Do you really save money turning off the lights when leaving the room even for a brief moment?

So what about for ovens? Well, we measured the warm up energy required for both of the ovens described above. Here are the numbers for our newer 53 liter oven:

oven statekWh required
room temperature to 120 °C over one hour0.29 kWh
hold at 120 °C for one hour0.16 kWh

So, the energy required to heat the oven up to 120 °C is about the same as running the oven for two hours. Therefore, as an approximation, if your glassware oven is off for at least two hours, then you start saving energy.

At this point I can hear hardcore synthetic chemists (you know, the kind who have an obsessive drive to eliminate water) crying out – but we need to dry our glassware for a full night!

Okay, is that true? Well, the book Techniques in Organic Chemistry says

Wet glassware can be dried by heating it

in an oven at 120°C for 20 min.

Techniques in Organic Chemistry, 3rd Edition, Macmillan, 2010, by Jerry R. Mohrig, Christina Noring Hammond, Paul F. Schatz

Okay. That seems a bit short to me, and they don’t give any references. Let’s dig deeper.

And, many minutes & several books later, I have yet to find a good study. Some people say you should dry overnight, others say that even for a Grignard reaction (infamously water sensitive) a mere 20 minutes at 120 °C in an oven is sufficient.

So…I guess it’s up to you to decide. In our laboratories, we went for a middle approach. Our older, less efficient ovens were placed on timers to shut them off between 9 pm and 5 am on weeknights, and all weekend. We elected to keep one of our newest ovens on 24/7 – not because we believe glassware needs to be dried overnight, but because some chemists like to work late at night or on the weekend (hopefully with a safety buddy of course).

programmable timer

Okay! Two questions remain. 1) Have our lab members left the timers attached? and 2) how much energy have we saved?

Answering question 1 is important – if researchers find more sustainable methods inconvenient, they may just…remove the timer. By ensuring that one oven was always on, and setting the off time of the other two ovens well outside of normal working times, so far the timers are still attached. The same can’t be said for the timers attached to our rotovap baths, but that’s another story…

Now, question 2: how much energy has been saved? With our two older ovens on timers, and factoring in the required heat-up time, we are saving about 50 kWh per week, or about 200 kWh per month or 2400 kWh per year. That’s about one quarter of the electricity used by an average American household (yes, American – American households use noticeably more electricity than most countries, even comparing across ‘developed’ societies).

So, was it worth it to put our glassware drying ovens on timers? Yes.

What’s next? Demanding that suppliers create ovens that are ever better insulated. In the meantime, we encourage you to start saving serious energy!

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