Personally I think a kitchen type oven is much better for tempering than an actual "heat treat" oven. Since acquiring digitally controlled heat treat oven, I've discovered that if a heat treating oven is set to ramp up too temp at it's max. blades routinely come out "over tempered"...or tempered beyond what you wanted. If you slow down the ramp to 1/3 of your tempering temp per hour, THEN have it hold for 2 hours, it works fine.
For those who forge, most of the steels used have tempering temps in the lower range (500F or less) and a kitchen oven is just the ticket....as long as you check it to ensure the temps you set on the dial are actually what your getting in the oven.
I have a kitchen oven in my shop that I have placed a couple of fire bricks on the bottom shelf (this keeps the temp very stable after pre-heat) and use it for the majority of my tempering. About the only time I ever use my heat treating oven for tempering is when the required temps are more than the kitchen oven can provide.
