Have been by these lately and will post pictures once the first loop is made..Got a 10 watt panel for under $40 and bought a few baseboard water heaters from menards on sale..Gonna play with a small array for this winter and next summer have enought to turn off the water tank and just circulate thru 40-50 of these.. Its in the 40 right now with wind chill and one is boiling water with a cap on it(loose fit foil with rubber band... these are no joke guys and they epoxy into a 2 inch pvc tee fairly well...Scuff the glass first but be careful..I was tapping a tight one in and cracked the top and it exploded loud!..air rushed into the vacuum.. The only place they lose heat is the top where the two glass walls join but it will be in water once they are in place..
