Where is the thermostat for the heat? It sounds like you're returning to 69 because the heat cuts out when the heaters raise the temps. You need to raise the temp of an area that wont affect the reading that the thermostat gets.

You can also get those plastic sheet insulating kits for the windows. I use those in my herp room and they do wonders. I keep the thermostat for the house at 69 and the herp room gets to 73 alone just with the windows plastic'd.