46 degrees outside this morning. The house was 68. I didn't have the system on to call for heat yesterday as I was trying to adjust the idle burn down to a minimum. I forgot to set the TT for heat last night. This morning I thought Great! the radiant heat from the boiler was keeping the house warm in these moderately chilly temperatures over night. Then I hit the floor registers with the IR thermometer,.....sure enough,...80 plus degrees at some. Then it hit me,.....my hot water to hot air coil sits several feet above the boiler and some 10 feet away. The coil was hot. I didn't consider thermosiphoning in my piping design. Not a huge deal now other than wasting a little coal but come summer when I'm burning for domestic hot water, I definitely don't want the coil hot. What's the best method to prevent thermosiphoning? An anti thermosiphoning loop or a spring valve,......or both? I have a ball valve before the circulator on the return but in my haste to get he system up and running and my cheapness,...I mean thriftiness,....I didn't put a ball valve on the supply loop. Haste makes waste,..as they say! Lol!