It's a debate as old as mildew itself: How do you dry your clothes during winter when it's pouring outside, damp inside and dryers are an ecological no-no?

For centuries, when we weren’t using them to build blanket forts, we’ve been drying our clothes on clothes horses in the warmest room of the house. But environmental health experts tell us that's a soggy disaster.

According to building research institute BRANZ, hanging wet clothes inside during winter could release up to five litres of water per load of washing into your home each time, two litres more than cooking, or an adult breathing. In fact, the research found drying clothes inside could be a contributing factor to mould and mildew growth in some homes.

"Imagine it's a big family that does three loads, it would be 15 litres of water,” says Dr Mikael Boulic, senior lecturer at Massey’s School of Built Environment. “It's like living in a sauna, more or less.”

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But anyone who has collected a load of laundry in the evening pretty much as damp as when they put it out that morning knows that line-drying in winter can be unreliable at best, impossible at worst.

So if we can’t dry them inside, and we can’t dry them outside, where are we supposed to dry our clobber in winter? It’s “quite tricky”, says Boulic. Oh.

Dryers aren’t all that great environmentally – the average household could save 27kg of CO₂e per year by line drying instead of using one, it’s been estimated. They can also chew through expensive power if you let them run longer than necessary.

But those impacts aside, they are the best way to dry clothes in the damp months. “When it’s wet outside, and you’ve run out of clothes for the kids, that's when dryers have their place” Gareth Gretton from the Energy Efficiency and Conservation Authority previously told us.

Make sure yours is vented outside though, through a window or wall, otherwise you’ll just have the same dampness issues.

Some dryers detect when the clothes are dry and stop, but if yours doesn’t, periodically check to make sure you aren’t wasting energy and money.

It might also be worth investing in new technology like heat pump dryers, which are much more efficient and cheaper to run, if you do a lot of laundry.

If you don't have a dryer, or access to a covered outside location, it is best to dry your clothes in your bathroom and run the extractor as long as you can.

If you don't have an extractor fan – and you should really get one for the same reasons you shouldn't be drying your clothes inside – you should have at least two windows open while the clothes are drying.

"It's what we call cross ventilation. If you open two windows on each side of the house, a draught is created, because there is always a wind coming from one side”, says Boulic.

If it’s too cold to have the windows open, you’re back to square one – and the answer might be not washing your clothes as often.

Once or twice a month might be OK, but doing multiple loads per week will really start to cause you trouble as moisture builds up in the house.

“Our homes are full of hygroscopic material – it's all paper, wood, carpet, clothes, all materials with the capacity to hold moisture,” says Boulic.

“So even when your clothes are dry, this moisture will stay inside your house, and it's quite hard to get rid of it without ventilating it as much as you can.

"Mould is always there, you always have some spores. The food is always there, our homes are full of wood and paper, cellulose which mould feeds on. If you bring water [inside your home], the mould will grow, quickly."

A damp house will also cost a lot more, and be harder, to heat. Boulic recommends using a dehumidifier during winter, to draw the dampness out of the air, if it’s a constant issue.

Over on social media, the indoor clothes drying community of Twitter has been debating winter laundry, and the culprit of damp Kiwi houses. Some suggested part drying your clothes on a line or clothes horse, and finishing them off in the dryer. Others, nipping big loads round to the fast industrial dryers at laundrettes.

One suggested drying clothes under the heat pump, while another said they dry theirs in front of a log burner.

Do you have any winter clothes drying tips and tricks? Drop us a line at homed@stuff.co.nz and let us know.