A few facts: New (to me) Water Furnace system. Radiant heat throughout the house. Some days it is a bit chilly outside, some days it is warm. My wife and daughter wear sweaters and complain they are cold on the chillier days. I get yelled at because I don't want to turn on the heat. I would like to prolong the Indian summer months and save a few bucks by not turning on the heat. I guess I learned this from my Dad who was a fanatic about waiting and waiting until turning on the forced air heat. He almost made us all feel guilty about it when he turned it on. Anyway...my question is, during these transitional weeks/months like we see in the fall and spring, does it really cost much to turn on the heat and set the thermostats to around 67 or 68 degrees or should I hold out as long as I can? Keep in mind that on some days the thermostats will not be calling for heat and I will just be heating/maintaining heat in the buffer tank. Thanks in advance for any advice.