I live in Massachusetts, my house is 112 years old and has a fieldstone foundation, and I have radiant heat on the first floor. During a cold snap, where the temperatures dip into the teens, the first floor of my house has a hard time holding its temperature. The heat is set to 64 degrees yet during the cold snap it can drop to 56 degrees within a couple days. Any idea what causes this or how to fix it? I'm not sure if my radiant system is not robust enough, if I need additional insulation, or if there's some other solution.