I've been brewing 4 gallon batches on the kitchen stove, using two 5 gallon canners. Mash with about 2.5 gallons of water, sparge in the other pot with 2 gallons of water, combine them and boil. The high-output burner on the kitchen stove was just enough heat to boil that much wort.
My last batch, I changed everything and it was somewhat easier. I put a little less than 4 gallons of water (didn't really measure it) in the kettle, added the grain, then added more hot water to fill the kettle to the top for the mash. It was a lot easier to maintain the temperature for an hour with the extra volume. Then I pulled the bag out, squeezed the heck out of it, and I didn't sparge. The overall efficiency seemed about the same.
Then I boiled it outside on my new turkey fryer burner, so I didn't steam up the house.
I need to get a 7.5 gallon pot so I can do full 5 gallon batches. But no hurry because 4 gallons is a good batch size too, and I have 4 gallon carboys...
ETA: TheMadKing and I must have been typing at the same time. His process is almost identical to how I was doing it until I went full-volume mash. He used a bucket, I used a second canner.