For lacto-fermentated vegetables (cucumbers, green
tomatoes, red tomatoand pepper and onion relishes I ferment on an open shelf in my kitchen in lidded quart glass jars (using whey, following recipes from "Nourishing Traitions"). The temperature varies from seventies to eighties depending on the outside temperature, but I have consistant success. I also cover the jars with a dark cloth to keep out the light.
I haven't made yogurt for years but we did not have electricity then and it seems like I remember heating
water on the woodstove to put in insulated box, we didn't make much yogurt just drank a lot of goats
milk.
I incubate tempeh in my oven with the forty watt oven light on and sometimes add a kettle or two (in the winter) of
hot water to reach a steady 85 to 95 degree temperature.