Ours is a Mitsubishi MJE16VX, it says. The Beloved Stoker read all the reviews before picking this one. It claims to be about 200W. The tank is probably about 5L.
It's important, when you think about its contribution to your energy bills, to remind yourself of the cost of repainting or replastering instead. And as others have said it reduces (though not to zero) the amount you have to spend on heating just to draw the moisture out or to dry clothes.
Another useful tool we have is a Kärcher handyvac-cum-squeegee which sops moisture off the windows very efficiently.
I don't think there is any way to build a home in England which is well insulated and draughtproofed to keep heat in but also able to discharge surplus moisture out. Victorian homes are designed for inefficient open fires which dry everything out very nicely. Modern buildings stay warm but just breed damp. The Swiss can build beautiful warm cosy chalets to keep the winter night out until you leap singing from your slumber into the crisp morning air, but it's the low-humidity crispness of the climate that makes it work.
We suffer from a poorly insulated1 1960s flat roof which creates the terrifying phenomenon of Cold Bridging---condensation forming on wall or ceiling surfaces rather than just windows. Even if the water outside isn't penetrating right through then it may be compromising the insulation of your wall and encouraging condensation; through stones might also be culprits. Free air movement to problem corners, running the dehumidifier and turning the thermostats right up are, between them, just about an adequate answer for us.
1. With chicken wire and shredded cardboard. I don't know what its design life was, but I doubt it was 50 years.