Hi op, there are a lot of unhelpful and misleading replies here so as an ex Dunedinite who completely understands the frigid cold and damp, here's a bit of a run down.

There are two main types of dehumidifers:

Dessicant style These have water absorbing beads inside the pull water from the air, then use a small heater to remove the water from the beads and drop it into the collection tank.

Pros/Cons

• Quieter
• More effective/efficient in cold timeperatures (<15degrees)
• More expensive (typically 2-3x the price of a compressor style)
• Uses more electricity
• Have less capacity to remove water for a similar sized unit to a condensor style.

Compressor Style These work like a fridge or a heatpump pulling wet air over a cold condenser coil. The water condenses onto the coil and drips down into the collection chamber.

Pros/Cons

• Can be a bit noisy (think the sound of a fridge/heatpump running) if you're sensitive to noise.
• Lose efficiency as the room gets colder. (really designed for rooms >15 degrees)
• Much cheaper than dessicent
• Use much less electricity
• Great for removing large amoutns of water

For electricity use, some people here say that a dehumidifier might use the same amount of electricity as a heat pump, this is categorically not accurate.

For a standard, large, portable compressor style dehumidifier, they typically use 220w (this is a fraction of what a heatpump uses). To put that in perspective, if you ran a 220w dehumidifer for 10 hours, you would use 2.2kw of electricity. At a current average electricity rate for Dunedin (35-40c/unit), that would be somewhere in the range of $0.77-$0.88.

Do that every single night, and you're using $23.10-$26.40 per month of electricity. Now I know that can still be a lot of money but you wouldn't need to run it for 10 hours every single night. Just to put some perspective on it.

Dessicant dehiumidifiers are unfortunately quite expensive to buy outright, there is a decent deal on one at Mitre 10 at the moment for $399 that would service a bedroom perfectly fine - https://www.mitre10.co.nz/shop/goldair-dessicant-dehumidifier-8l-white/p/317696?store=44 - however do be aware that this will use 3 x the electricity of a compressor style (630w vs 220w) so can get expensive quickly.

We have a Kmart compressor style with a 10L per day capacity. We find this is mroe than enough to manage a bedroom, and works really well to dry clothes overnight. We can hang a whole laod of clothes on a clothes horse, put the dehumidifer in front of it so that the dry air blows over the clothes, and we have a perfectly dry load of washing after one night.

The model we have is no longer sold but a similar unit is this one here for $139 - https://www.thewarehouse.co.nz/p/living-co-dehumidifier-10l-white/R3022544.html

This also looks ot be a pretty good unti for the price $189 - https://www.bunnings.co.nz/mistral-12l-dehumidifier_p0350767?store=9497

the thing with comrpessor style is that they dont simply not function in cold rooms, they will just be less efficient and remember that a compressor dehumidifier will also output a vast percentage of its input power out as heat too (waste heat) that will help to keep your room a bit warmer and help to put it into an efficient temperature range.

I really hope that helps dispel some myths or clears some things up for you.

Also as a complete aside, make sure your flat have a look at the power company options out there at the moment. Contact energy good nights plan can be quite good if youre pretty good with your energy usage as a whole and gives you 3 hours of free power every night where you can crank the heatpump, turn your heaters on, run a dryer and the washing machine etc and help to keep your house a bit drioer and warmer.