Hi Bob
I run both, started as oven cleaning only and got into window cleaning due to a request from a commercial customer. Now oven cleaning is still the main side of business but windows catching up steadily. Soon won't be enough days in the month to meet demand!
Oven cleaning is still a growing sector, many people still aren't aware of it but the majority will become regular customers once they have found you. Ask your customers if they would have their oven cleaned if you offered the service to gauge demand. Not expensive to get up and running and I find the two work well together, most of my window customers have come from having their oven cleaned. I also offer a start up package including training, dip tank, all equipment and materials needed.
I have been running 2 vans but get a new van next week to run both from.
Give me a call if you have any questions, numbers are on websites.
John