I'm thirty days into flowering my first grow down in the basement of my 1850's farmhouse. I started in a bedroom closet on the west side of the house but the first wave of hot weather pushed the temp into the 90's and I knew there was no way that was going to work. So I wrapped my 6' by 8' coal bin in 5 mil plastic sheeting, put some dropped ceiling tiles (basically fiberglass bat) on the dirt floor to help hold down the humidity coming from the soil, and put some pallets on top of that to keep things level and allow some leeway with spills. I run two 250 watt lights and they manage to keep the room at between 60 & 70. From what I read that's rather low and may invite root rot if my tank gets too cold but so far so good. It also generally slows plant growth but my girls are flowering their hearts out. Makes me wonder what they would have done at a higher temp.
I think the real problem is going to be humidity, which has been as high as 100%. Sounds like bud rot just waiting to happen. I keep the tried & true oscillating fan running on my girls to keep the creepy crawlies off them. I'm fortunate to have the exterior door to/from the basement right outside the room and it's oriented to the East so the sun will shine almost right into the room in the mornings. So I open it up whenever I can to drop the humidity, raise the temp, and refresh the air. I actually have the boarded up window from the coal shoot right in the grow room and I've pondered hooking up ventilation to bring warmer/drier air INTO the room (how's THAT for a change!) but I have some security concerns there. So far what I've been doing seems to be working (touch wood!).
When this batch is hung up drying I may strip the room bare and encase it in foam board in order to provide better heat retention. But even with such efforts I suspect that as winter approaches I'll probably have to move my grow back into the second floor bedroom. I just can't justify actively heating the room, and I'm not clever enough with HVAC to tap the domestic heating into the room. But hey, half the fun of this hobby is the engineering! Good luck on your grow and keep us up to date!