It's very low for a daytime temperature. Maybe it makes sense with the gas crunch and energy prices in europe, but the specific thing that bothers me about it is hiding that number below the "advanced" checkbox. I don't think people who are used to paying for winter time heating set their thermostat to 68, so using that number to calculate how much a heat pump costs to run will artificially lower the cost of the heat pump in this calculator.
I'll take a look back at the residential energy consumption survey and the exact distributions.
The Manual J (industry standard approach to load sizing) uses 70 dF for heating and 75 dF for cooling as its defaults, so we could definitely update the defaults to those, too.
