I somewhat maligned the eco cute in how much electricity it was using while we were away. Here's a graph of the daily usage. You can see that it's using more for the first week (average 6.6 kWh/day), then very little for several of the remaining days (average 3.9 kWh/day). The least the house used in a day was 2.1 kWh, ie running at a little under 100 watts. Looking at the hourly usage for that day, there was a flat graph whereas there are usually some bumps in the nighttime up to a few kWhours each hour while the Eco Cute is doing its thing. Taking this 2.1 kWh/day as the house base usage, for the first week the Eco Cute was using 4.5 kWh per day, then for the rest of the time 1.8 kWh per day. At 9 yen per kilowatt hour, this is hardly going to break the bank!
From the perspective of heat, this heat is going to be leaking into the house, so it gives us an idea of the extra heating bonus in the winter, and also the extra over-heating burden in the summer.
As far as working out what goes on inside the Eco Cute's brain, it appears that it calculates how much hot water is needed based on the usage over the past week, so for the first few days while we were away, it was labouring under the misconception that we were about to run baths of water. Doing this led to a tank full of hot water, leaking 4 and a half kWh of heat into the house each day. After a week, it realised that we weren't using any water, so it started producing more modest amounts, or in fact none for a couple of days.
