How do I get an accurate temperature reading?
My new pool (25,000 gallons) has an automated system that has its own temperature gauge in the plumbing at the equipment pad, plus the heater has a temperature gauge and I keep a floating thermometer in the pool. Since day one they have never agreed with each other. The two gauges at the equipment are off from 1-3 degrees from each other, but they can vary wildly from the gauge in the pool. The pool builder and servicing company say to ignore the "cheap" gauge in the pool and trust the ones at the equipment. But weÃ¯Â¿Â½re now having doubts about that. The pool wasnÃ¯Â¿Â½t swimmable until early July so it was peak season, very warm and we get all-day full sun exposure with no shade. In that context the difference was 6-7 degrees between the equipment and the pool gauges, with the pool thermostat always lower. Now weÃ¯Â¿Â½ve had some overcast days in the low 80Ã¯Â¿Â½s and the difference is severe. The pool says 72 degrees with the equipment saying 85/87 (and we have the heat pump set to stop at 85).
The thing is, there is no way it feels remotely like 85 degrees when you swim in it. It felt almost warm to get into before and now everyone is a cold. So while it may not be 72, of the dozen people who were in it in the last week not one would say it is remotely close to mid-80Ã¯Â¿Â½s, or even 80.
I bought a more expensive digital floating thermostat to see if that made a difference and it too is registering meaningfully lower temps than the equipment if not exactly the same as the previous floating one.
Bottom line, is it true that the equipment readings should be more accurate than the pool readings or is it possible the readings in the equipment could be skewed hot (like the way readings of outside air in your car are always higher than reality when the car has been sitting outside in the sun on a hot day)? And is there any way to get a truly reliable measurement of the pool temp independent of my equipment?