Mechanical ventilation - to use in summer or not?

Mechanical ventilation with heat recovery is great for the cooler months, you get that fresh air feel without having to open windows and without losing all that heat you've built up with your central heating.

The question is though, should you leave it on during the summer or should you rely on opening windows? If you leave it on then it is using energy to ventilate your home, although with a summer bypass function there will be no heat recovery. The other advantages include not having insects coming in to bite at night or buzz around your food, and it reduces the disturbance from the inevitable increased noise in summer - planes flying, children playing, barbeques in the garden.

But it does use energy and you could just open the windows to create air movement and a cooling effect.

The first year we had our system we kept windows shut and the MVHR switched on - we knew the horrors of a fly infestation and didn't want a repeat! In a hot spell it was quite hot in the house, but then it would have been hot if we opened the windows; the MVHR certainly didn't act like an air conditioner.

This year we are using windows and blinds during day to keep sun out and allow fresh air in; we're putting up with daytime insects. Once there are lights on in the evening we close all the windows and use the MVHR to ventilate the house and that's successfully kept away the mosquito bites!

We try to keep our electricity bills down in other ways, i.e. nothing is left on standby, broadband is turned off when we're not using it, we use a laptop rather than a pc and this is put on standby if not in use for more than 10 minutes and turned off at other times when not being used.

So maybe the MVHR is our electricity indulgence, along with the fridge/freezer and phone. However, used intelligently we feel it contributes to good ventilation of our home without excessive energy use.

Has anyone else out there had experience of using these systems in their own home?