October 1st we turned the radiant heat on in the sand high mass collector. There’s a delicate balance between turning it on early enough so the sun is still heating the hot water panels on the roof, but not so early that we overheat the house. The one year I turned the sand on at the end of October, we were cold for the next several months. Since then, I have been turning it on in late September or early October (2015 post). Most years, we have turned the sand back off because it got too warm.
This year was no exception. The sand warmed all the way up to 86F right before a week of 70F+ weather forecasts. So I turned the sand back off on October 15th. Or so I thought. The house kept getting warmer. I must have been too tired when I thought I turned the sand off. What I actually did was turn the slab radiant heat on too. Guess we will be leaving the windows open for a few days to cool down.
Outside it hasn’t cooled off much, so we don’t particularly need the heat yet. For reference, here is our photovoltaic production for the year. The hot water panels are tilted more towards winter solstice sun angle, so they will be producing more heat later.