# How can I find an efficient electric oven for my kitchen?

Posted Thu, 03/06/2014 - 14:03

1.

hi Kathy, where are you living ??

could you estimate how many hours per day/week you normally use your oven for baking ?

Posted Thu, 03/06/2014 - 14:13

2.

Hi Jim,
I'm in WA state, 99324. I use the oven about 4 hours/week for baking, usually at 350 degrees.
Thanks

Posted Thu, 03/06/2014 - 14:17

3.

Let's assume that your oven uses a maximum of 4KW of power while working

( probably much less because it goes on and off to maintain set temperature )

4 hours X 4KW = 16 KW/h of energy

probably less than 75% of this total because of the cycle
so ~ 12KW/h

You can understand your cost for using your oven by multiplying 12 KW/H by your electrocity tarrif/rate. ( 12X rate )

That heat, no matter how insulated your oven is, is going to end up in your house, heating the kitchen up . There is no way around that, unless you have very efficient hood setup/fan that you could use to exit this heat while it moves up by convection toward the exterior of the house.
( i see your climate is mostly cooling dominated )

If you are using AC to cool your house, you will probably need to cool that additional heat
with the COP of your AC ( so you can again add from 25% to maybe 50% on top of the previous cost )

Lastly, adding thermal insulation on the oven ( i mean getting one with a better insulation ..do not attemp this unless you know what you are doing ) would lower energy consumption of the oven while it is trying to maintain a set temperature ( which usually have a very high Delta T with ambient air ) and would also impact the total heat that is dumped into your house.

This is less important when moving toward cold climate where most of the time
the oven is only helping out on heating the building.

hope this helped ( maybe off topic a bit ..but i enjoyed typing it !! relaxes me! :p )

Posted Thu, 03/06/2014 - 23:21

4.

I sincerely doubt the oven is leaking anywhere near 4kw / 13,648BTU/hr of heat into a 70F room at 350F oven temp, or even 3kw. It's probably more like 0.5-1kw, but let's analyze it, eh?

Assuming the oven chamber is roughly a 2' cube that's about 25 square feet of surface area, so to hit the 4kw / 13,648BTU/hr number it would be losing about 550 BTU/hr per square foot. At a temperature difference of (350F-70F=) 280F, that's an implied U-factor of about 2BTU per square foot per degree-F, or R0.5.

Even a tempered glass single pane oven window would be 2x that!

Most ovens would have at least 3/4" of rock wool or fiberglass insulating most of it, which would be around R3, and while there is some thermally bridging steel and some air leakage, the the average performance is probably no less than R2, or U0.5, which would imply it's dumping about U0.5 x 25' x 280F= 3500BTU/hr or 1026 watts into the room. That's a pretty significant space heater no matter which way you cut it, but probably worse than reality.

Another way to analyze it- there's about a 100F delta between the ~6 square foot 175F cooktop and the room, which would mean it's radiating something like 1200BTU /hr from the cooktop. The sides are only about a 50F delta, and there are probably only 3 sides exposed, call it 15 square feet, which ends up at about 1500BTU/hr of radiated heat, or a total of about 2700BTU/hr (790 watts) being dumped into the room. That's probably an upper-bound kind of number, but let's assume it's real, call it 800 watts.

So, 800watts of average power at 4 hours use ends up at about 3.2 kwh/week (which is a heluva lot less than 16kwh, eh? ;-) ), and in a heating-dominated Walla Walla climate that heat is offsetting your heating bill a bit for 3/4 of the year too, reducing the net energy use, call it 3kwh-net after heating benefits less air-conditioning losses. That's on the order of 150 kwh/year, which at the 9cents/kwh WA type residential retail rates costs about \$13/year, assuming it's truly 4 hours EVERY week, even while you're on vacation.

Posted Fri, 03/07/2014 - 16:12

5.

Heating dominated climate? i looked it out on weatherspark and it seems like 0c+ all year round ???

of course i was relating to maximum consumption Sifu Dana ,
dind't want to bother with getting into the insulation formulas :p ( lazy arse )

Posted Fri, 03/07/2014 - 16:58

6.

Seems to me the stove, oven, cooking machine technology and design solutions are not too well thought out. We are probably in the middle of a transition but manufacturers have not yet found solutions for integrating the methods, the ergonomics and energy smart designs into new kitchens.

Microwaves have been around for a long time yet we still have not found a way to integrate them that makes any sense. They are hung from the bottom of kitchen cabinets, wasting counter space and or hanging over hot range tops – that is just plain dangerous, bad use of space, poor design and dirty.

Microwaves, full scale toaster ovens, range ovens – none have been optimized. Ranges take up way too much room and waste too much heat and add irresponsible cooling system loads. Toaster ovens are more efficient and compact but are not designed for in-cabinet installation and are not yet able to replace the range oven.

Range ovens seem to be gigantic space wasters. Even if I put in a hind leg of lamb, or a 20 lb turkey, or a couple of rib racks of venison, there seems to be a lot of wasted space in the range oven. Toaster ovens are trying to compete with toasters, so they are held back functionally from competing head to head with range ovens.

I notice that microwaves and toaster ovens are being sold as competitive with each other. That of course is bogus as their cooking functions and applications are entirely different. Try searching one type and you get the other as well on your browser.

I would like to see a reliable, comprehensive comparative analysis of energy use, fully loaded, to account for waste heat and cooling loads, operating cost/type of stove and type of cooking; etc.

Posted Sun, 03/09/2014 - 16:28

7.

In case some GBA readers missed it, here is a link to an article on induction cooktops: An Induction Cooktop for Our Kitchen.

Posted Mon, 03/10/2014 - 05:52

8.

Great discussion. Our heating degree days are about 5967. It seems warmer than that here; our heating bills are less than our a/c bills. Haven't reduced that to BtUs, however.
I like Fitch Plate's comment: " I would like to see a comprehensive comparative analysis of energy use..". Exactly. refrigerators, dishwashers, water heaters, etc are being made more efficient, yet, the oven sits like an elephant in the room. At the very least, please offer the consumer (me) some information.
Martin's comment on induction leads me to wonder if someone will design an induction oven. I use an induction cooktop,but it doesn't substitute for an oven. THAT would be efficient, IMHO.
Kathy

Posted Mon, 03/10/2014 - 11:34

9.

I looked at the Blog which Martin referred us to. Although induction stove tops are much more efficient if you consider the BTU/cooked item (< 85%, faster, less energy, and cleaner). But there would seem to be no payback (yet) when looking at fully loaded costs (buying, operating).

Comparable retail prices show that stoves with induction burner tops are priced \$700 to \$1500 more than gas and electric. To save a couple of \$'s/mo on energy bills when it means paying compound interest on the money through a mortgage or renovation loan would not be effective.

In western NY where I am, electricity is quite high so I think you will find natural gas and even truck delivered propane are actually competitive with electrical resistance burners. Need to run the numbers to compare with induction.

Here is what California consumer energy centre says:

http://www.consumerenergycenter.org/residential/appliances/ranges.html

And here:

Enter your local prices into the correct column and see which type of fuel is the best price for BTU's delivered.

Heating fuel comparison calculator:

www.eia.gov/neic/experts/heatcalc.xls‎

On a cost per BTU basis, wood stoves look pretty good. But cooling loads are hefty.

Wonder what % of unused stove top and stove body heat (from gas and electric) goes up the exhaust vent vs contributing directly to space heating?

Posted Mon, 03/10/2014 - 12:58

10.

An induction oven that works directly on foodstuff type materials has already been invented- it's called a micro-wave oven, which heats the food directly by inducing a high frequency (~2450 megahertz) electric current in the outer layers of the food being cooked, heating it up.

Induction cook tops running at the muchas mas lower powerline frequency of 60 hertz ( that's 40 million times slower than the microwave oven) need something that conducts electricity a quite bit better than most food to convert the slow AC magnetic field of the cook top into an electric current in the cookware, which heats up the cookware directly. If you were to put your goods to be baked into a steel box it would heat in the presence of a 60hz magnetic field, but it would burn the food wherever it contacted the steel box, and you'd still have to insulate against the heat coming off the outside of the box.