I can't speak for dehumidifers (never tried one), but I was in a similar position as the OP, with a 2-bed bungalow, except that I already had an extractor hood in the kitchen, a bathroom extractor, condensing tumble dryer and I made use of the night vent lock position on the windows. Between October and April, every window would have excessive condensation overnight.
I fitted a PIV unit in the loft, and the overnight window condensation was completely gone within a couple of days. I've now had the unit fitted for around 18 months and I'm very happy with it (it's a Nuaire Drimaster). My gas usage for heating has actually decreased, which I suspect is a combination of it requiring less energy to heat "drier" air, plus I now have controlled ventilation, rather than leaving windows open and cranking the heating up further. The only time I can get condensation forming is if I shut the door to a room, and close the cellular blinds completely, and even then it's about 1cm strip of light mist, and only on the old mid-90s double glazed units. Before PIV, the blinds could be open, all doors open, allowing good air circulation, and water would be dripping over 50% of the height of the panes, including on the newer low-e panes. If I bump up the speed of the PIV unit, I can even get rid of that 1cm strip, but then I'm over-ventilating for no real benefit.
So, it's PIV for me. I also considered MVHR - it's usually easy to fit in a bungalow; but the payback period was too high for me. PIV can be fitted for around £300. MVHR will be several thousand by the time that you've added in the unit, all the ducting, plus proper commissioning to balance flow rates. PIV commissioning is a matter of picking the correct speed based on building volume.
I don't have a heater on mine, and don't feel a need for it. You're supposed to install the diffuser a certain distance from any walls to avoid drafts (just check where your joists are - I had to compromise somewhat, but still within the recommended vent-to-wall distance for the speed I'm using). As you're using electricity to heat, it might make sense for you to get the heat option (you can always turn it off), but the flow rates aren't high enough to make much difference to temperature either way, although be aware that for the basic fans you can usually power them from the lighting circuit, whereas if you fit a heater you'll have to break into the socket ring.
Thank-you for the detailed post which I have only just seen.
I went for a PIV with heat with controls in the diffuser. Installed it myself and paid an electrician to wire it into the socket ring.
The windows in all the rooms of this 2 bed bungalow would be soaking wet top to bottom in the mornings, I would have to go round 2 or 3 times and wring out the 2 cloths many times, then open the windows slightly to air the room and finish off drying the windows, which is not something I wanted to do in the colder months as it lets the heat out.
The day after turning the PIV on there was only condensation on the bottom 2 inches of the window of the room I slept it.
Since then there has been no condensation on any of the windows, quite amazing and I only have it on speed setting 2.
I may turn it down to speed setting 1 but want to test things as I am going to do a clothes wash and dry in the utility room tomorrow.
Setting 1 will only use 1.6 watts.
I had the heater set point in the middle setting for the first day and then turned it right down so it has not been activated since.
It is cool in the hallway but the heater would cost of £50 a month to run and it only tempers the incoming air.
I only fitted a trickle vent to one window, I do have 9 more if I need them but I read that some people regret fitting them because they let in extra noise.
The only downside is the hallway smells of loft
Do you know what I mean?
Although I cannot say I have noticed the difference in air quality I am sure it is fresher than before installing the PIV.
The flow rate is 20 litres a second at the moment.
I used to get some black mould around the window reveals, luckily nowhere else.
How do you find it in the warmer months from April to September?
I ask because in those months I used to get white mould growing on my new furniture, bed, wardrobe, sideboard etc. Also anything kept in the bed drawers, wardrobe and desk would go mouldy, white mould. So I have had to empty all those places out, I hope to be able to put the stuff back in the drawers later in the year.
I think I will need the PIV to run 365 days a year but when the loft air is warmer than the bungalow air I wonder if this will cause the white mould to grow again. Not sure if the warmer air would also be more humid air.
I would be interested to hear your experience of the warmer months.
At the moment I have it on default setting.
"At loft temperatures below 19°C the unit will operate on
“Normal Operation Mode”.
At loft temperatures above 18 C but less than 24 C, the unit will
switch automatically to
“Intelligent Heat Recovery Mode”.
At loft temperatures above 23°C the unit will switch itself automatically
to
“Standby Mode”."
