How much heat a house needs in Kosiv, Kosmach or Vorokhta: 30 winters of degree days

Heating a house in Kosiv or higher in the hills is usually judged on the seller's word: a lorry of firewood does the winter. We took 30 heating seasons, July 1995 to June 2025, of daily temperatures for six places and worked out how much cold each winter actually puts on a house. That figure converts into kilowatt-hours, and from there into money, for any particular home.

The temperatures come from the ERA5-Land model through Open-Meteo, on a grid of roughly 7 by 11 km. The model reports the height of its own grid cell, not of your plot, so read this as a comparison of places and winters rather than a forecast. We tested how close it gets against the Chernivtsi weather station, and the result is further down.

How much more heat does a house need higher in the mountains?

Less than people expect: from 1% more in Yaremche to 9% more in Vorokhta, compared with Kosiv. We measured it in heating degree days, using Eurostat's method. Every day with an outdoor mean of 15 °C or less adds the gap between 18 °C and that mean. A day averaging 2 °C adds 16 degree days, a day at 16 °C adds nothing. The season's total is proportional to the heat a house loses through its walls, roof and windows.

Height alone does not explain it. Kosmach sits 249 m above Kosiv and needs 7% more heat. Yaremche sits 151 m above Kosiv and needs 1% more. Yaremche lies in the Prut valley, and the model gives it a milder winter than its height would suggest. The rough rule these numbers give is 2.5-3% more heating for every 100 m you climb, and a slope, a valley or the wind can push that either way.

One more correction. The model places Vorokhta at 748 m, but the village itself is at about 850 m, and Yaremche also sits above its cell. The real heating demand there is a little higher than the table shows. We compared these places on roads, visitors and prices in the article on Kosiv, Yaremche, Vorokhta and Verkhovyna.

Turning degree days into kilowatt-hours for your own house

You need one figure for the house: its heat loss in watts for every degree of difference between the rooms and the outdoors. For a new house the designer calculates it in the heating section of the project. For an existing one you can estimate it from last winter's bills. Then:

Heat per season, kWh = heat loss, W/°C × degree days × 24 ÷ 1000

As an example, take an imaginary house whose designer arrived at 150 W per degree. That is not an average for the region, just a number to work with, so put in your own.

For this house, the difference between Kosiv and Vorokhta comes to about 1,200 kWh in a typical winter. The difference between a mild and a hard winter in Kosiv itself is five times that, over 6,400 kWh. To turn those kilowatt-hours into firewood, pellets or electricity, use the price-per-kilowatt-hour formula from our article on heating a house without gas.

The coldest night of the winter, and what to size a boiler or heat pump for

A boiler or heat pump is sized for the coldest night, not for an average winter. In a typical winter the coldest night in all five mountain places falls to about -20 °C, and over 30 years there were nights down to -25 °C in the hills and -28 °C in Kosiv.

Kosiv, the lowest of the mountain places, has the most nights at -15 °C or below, and the model puts the coldest night of the 30 years there too: -28 °C on 25 January 2010. On a still night, cold air drains off the slopes and collects in valley bottoms and the foothills. A house at the bottom of a valley can therefore have a colder night than a neighbour 200 m further up the hill.

What this means for a heat pump

An air-source heat pump gives out less heat and draws more power as the outdoor temperature drops. Ask the seller or installer for the unit's output table at -20 °C specifically, and set it against the house's heat loss on such a night. For the house in our example that is 150 W × (20 + 20) = 6 kW, if the rooms are kept at 20 °C. If the unit gives less than that at -20 °C, the coldest nights need a second source of heat: a stove, a boiler or electric backup.

Have winters become milder in 30 years?

Yes, noticeably. In Kosiv the first decade, seasons 1995/96-2004/05, averaged 3,964 degree days, the second 3,653, and the latest, 2015/16-2024/25, 3,374. That is 15% less heat than thirty years ago. Vorokhta fell by the same share, from 4,349 to 3,735.

Milder winters have not removed the cold nights, though. At the start of March 2018 the model shows -24.6 °C in Kosiv and -24.1 °C in Kosmach, and the 2021/22 season took more heat than a typical winter in Kosmach and Verkhovyna. So take your running budget from the last ten years, and size the heating for the worst night of all thirty.

When the spring frosts end and the autumn ones begin

In a typical year the last night frost in Kosiv comes around 23 April and the first autumn one around 17 October. In Kosmach, Verkhovyna and Vorokhta the frost-free season is a few days shorter still, while in Chernivtsi it runs a month longer.

On a building site this is the window for wet trades: concrete, screeds and render. Agree with the builder that footings are not poured before late April and that wet work on the facade is done by mid-October. We covered how winter shifts the whole schedule in the article on how long building a house in the Carpathians takes. Which heating to plan a new house around is something we talk through with every client who orders turnkey construction.

What to ask the seller of a finished house about heating

• How much firewood, how many pellets or how many kilowatt-hours went last season and the season before. The 2023/24 season was the mildest in 30 years, so a figure from that winter alone will understate your bill by about a quarter.
• What temperature the rooms were kept at, and whether anyone lived there all winter or only came at weekends.
• Whether there is a heating design with a heat-loss calculation. If there is, the formula above gives you your own estimate in a few minutes.
• What second source of heat the house has for frosts below -20 °C or a power cut.
• Where the house stands: in a valley bottom, on a slope or on a ridge. That decides how cold its nights get.

The houses and cottages we currently have for sale are in our listing of houses and cottages for sale in the Carpathians. For snow at the same heights, see the article on 30 winters of snow around Kosiv.