And the point of this thread is ... ?

What's the heat output of your system?

DJH, when did you put the heating on? Beginning of November?

Is that total energy or heating energy you are talking about?

I turned it on 2016-10-22. I don't have any power logging to tell me how much power the heater is actually pulling. It's maximum output is 1.8 kW and it's only switched on 1230-0730 by a timeswitch. We also used some additional 400 W bar heaters overnight sometimes in Dec and Jan as well, because we're trying to use as much power on E7 as possible rather than spread the heating throughout the day.

Another way to estimate the usage is to look at the total energy drawn from my supplier. The overnight usage each day this winter is: Nov 13 kWh, Dec 17 kWh, Jan 18 kWh, Feb 14 kWh. Those figures also include whatever the immersion heater for DHW took. That's limited to 6 kWh per night, but again I don't know how much it actually took. This year's figures are about 3 kWh per day more than last year, which was a very mild year.

It's partly because I don't have complete logging that I bother with things like turning the heating off. In theory it isn't necessary of course. I always keep the temperature above 20 °C so the usage figures are comparable to that extent.

Yes, the point is hopefully to motivate people to insulate, insulate, insulate!

"Yes, the point is hopefully to motivate people to insulate, insulate, insulate!"

... well, then, that is a very worthwhile point.

From what you say, one thing I'm particularly interested in is the role of your mvhr when solar gain kicks in, that "the MVHR summer bypass will operate to stabilise things" when that happens. Presumably, this is your experience of the effect of summer bypass mode, i.e. the mvhr helps with heat distribution around the house.

I'm interested as the theory would say that a domestic mvhr unit isn't capable of doing that, mostly based on the straightforward physics regarding the heat capacity of air (i.e. the lack of). In contrast to that, people on here do similar things, mostly with distributing pre-warmed air, who report positive effects (as I do). As such, it's useful to hear of your experience of mvhr heat distribution - am I understanding what you are saying correctly?

Yes, the 1.8 kW is the MVHR post heater. The power is limited by a flow rate sensor that makes it cut out if the flow rate is too low and by an in-duct temperature sensor that limits the power to keep the air temperature below the set point. And by the room temperature sensor; I think the unit has a controller that soft senses that (PID?) rather than a simple thermostat. It's a VEAB MQEM.

The MVHR does help to equalize temperatures throughout the building but it doesn't do a perfect job. As synggapa says, I meant that it takes excess heat out of the house via the extract vents in wetrooms and replaces it with fresh cooler air via the supply vents when the summer bypass is open.

Temperatures everywhere within the house are fairly close to the average. Those with southerly-facing windows get two or three degrees hotter whilst the sun is shining. I think the generally small variance is mainly due to the much better insulation in the outside envelope than in the inside walls and floor. I do expect the MVHR helps though.