The Curtain Bank, which re-upholsters and redistributes donated curtains, is in desperate need of more donations, it says.
Run by the Wellington-based social enterprise the Sustainability Trust, the Bank said ot could run out of stock by the end of the year.
Curtains are given out for free to people carrying either a Community Services Card, or a Super Gold Combo Card.
Twenty-five volunteers and two part-time staff work at the Bank, with the target of doing up between 2500 and 3000 curtains, to then pass onto around 600 families every year.
But the Trust said the waiting time was delayed by at least a couple of weeks, and it was limiting the number of curtains per family.
It asked people to donate good quality pairs of curtains, free of mould or sun-damaged, so they could be done up and given a second life.
Tessa received curtains from the Curtain Bank nearly a year ago.
"We just have one of those typical old Wellington houses - drafty, freezing, and lots of condensation on the windows," she said.
"We had an energy efficiency assessment, and new curtains is one of the ways that makes a big difference.
"I'm a student and a mum, and I just couldn't afford a house of new curtains, so I went to the Curtain Bank, and ordered them and six weeks later we had amazing new-to-us curtains."
Stocks running low, demand running high
Curtain Bank coordinator Lynley Wilson said curtains were assessed for suitability, then adjusted to people's window measurements, lined them so they were double-layered fabric, and then gave them out.
But this year, stocks were running low, she said.
"At the moment we have orders for around 500 curtains and in the Curtain Bank at the moment, we probably have somewhere between 150 to 200 pairs maximum."
She added that for many of the pairs of curtains they did have, it took a lot of work to get them to a good enough standard to be passed on.
That winter only just ended exacerbated the issue.
"It's still a very very busy time with the colder houses, damp houses," she said.
"We have a very large number of curtain orders, and we have had much less donations this year for curtains coming into the curtain bank, so we just don't have the supply that we need to fulfil the orders we have."
The Curtain Bank was created by the social enterprise the Sustainability Trust nearly a decade ago.
The Trust's communities manager, Susie Robertson, said the curtain shortage was impacting the bank's service. It had faced delays, as well as not being able to fulfil each order.
"Normally we aim for a six-week turnaround," she said.
"We're just not able to do that at the moment, because the stock of curtains just isn't great enough for us to be able to get those curtains out there quickly.
"The other thing is when people have put in orders for their living rooms and their bedrooms, we've had to go back and say, 'for the meantime, we're only going to be able to supply you curtains for your living room'."
The bank has faced seasonal problems in the past.
Curtains that sustain
Well-fitted and double-lined curtains are the second best way of stopping heat loss from homes, behind good insulation.
Even if a house is insulated, 45 percent of heat can still be lost through single-glazed windows. Curtains help stop around 60 per cent of that heat loss. But the materials used and the way they are hung have a big impact on how efficient they are at preventing heat loss.
Tessa said since receiving the curtains, her family had noticed the difference.
"Getting those new curtains in stops those transfer of heat. I haven't compared bills, but I feel like we don't use the heater as much, or it's not set as high.
"A little thing like these curtains just make such a difference to our quality of life really."
The bank needed both better quality and quantity of curtains, Ms Robertson said.
"The bigger the curtains the better, the longer the better.
"We don't take curtains that have mould on them, because that mould then spreads to our lovely curtains, and we would like curtains that are not sun-damaged.
"We want the people that we give these curtains out to, to feel good about themselves and their houses, and the situation that they're living in."
If you have any curtains to donate, there are drop off points at the Trust's building on 2 Forresters Lane in the CBD, as well as at the War Memorial Library in Lower Hutt, the Citizens Advice Bureaus in Porirua and Kilbirnie, as well as at Energise Otaki.