Have you read through all the previous discussions here about this issue? There is much info available in them. I linked one long one below but there are several others.

Basically it boils down to an unknown as it varies on the brand of the stove whether it will work or not. Some can make it work with great care and attention to detail, placement of the pot, pot size and shape, etc. Others cannot make it work.

Both types of canners are quite heavy so breaking the top is an issue. The cycling of the burners causes problems with pressure canning (not BWB so much) as it takes longer to bring up to pressure and the pressure in the canner fluctuates. Trapped heat under the canner also cause glass top breaking and warping of the pot.

The simple answer is yes to invest in a separate burner for canning. Some go so far as to install a separate coil-type countertop range in the house for canning.

Both electric and propane burners are discussed here in detail in those earlier posts. Propane is easier, cheaper, and offers more burner choices but can only be used in well ventilated areas while electric burners that are heavy duty enough for the weight and provide enough power to heat the pot are limited and more expensive but are available.

Dave

See also: http://forums.gardenweb.com/forums/load/harvest/msg0617391730130.html about electric burners.

Here is a link that might be useful: Has anyone been able to can on a glass top stove?

Thanks Dave,
I did research this problem further and have decided to buy a top-of-the line electric burner plate. I'm sure propane would be better but we don't have propane and I don't think the family is interested in dealing with a propane tank, etc. Your explanation has convinced me!
Helen

I don't have a pressure canner but I do have a Kenmore stove with a glass top and I've been using a BWB with it (as my stocked canning closet will attest) for a number of years with no problem. Also, I have used my pressure cooker (not canner) on it as well, again, no problems. Just my $0.02.

My SIL pressure cans on hers too, but my hair turns gray watching her :)

First, she knows it voids her stove warranty and does it anyway, using her mega weight All American canner that must be about the 22 qt size approximately (it hold two layers wide mouth pt jars).

The last time I was there that she was doing tuna, that gauge dropped with the fluctuating heat of the burner to within a heartbeat of being below pressure, over and over again during the processing time. Apparently its a safety feature with the stove top to avoid a buildup of heat under the pot bottom surface? Anyway, she is able to can tuna on it, but not without risk both to her stove and her product.

I have a Jenn Aire glass top range in the house we moved to in Nov - I won't be canning on it, I plan to use my propane burner outdoors, I've looked up the replacement price on that stove (entire stove, not the cooktop alone) and its not something I could easily replace (combination convection, downdraft vent, with about a $2000 price tag).

I just bought an LG glass top stove a few months ago. Fortunately, it has an extra-huge burner on it, so my Presto 16qt, and my BWB canner both fit without overlap. It is my understanding that having the actual burner too small, with the pan overlapping onto the "non-burner" surface is part of the problem.
I've been watching pretty closely during PC-ing, and have not had any trouble with the stove cycling on and off. However, I think that, given what I've read, I am going to be content with my 16qt, and not try to upsize to the 23 any time soon.
JMHO