What is the ideal humidity in a house? (UK guide)

The ideal humidity in a UK house is between 40% and 60% relative humidity for most rooms, most of the time. That's the range the Welsh Government recommends for health and comfort, and research on indoor air points to the same band as the sweet spot for keeping mould, dust mites and dry-air irritation down.

Short spikes are normal. A bathroom after a shower or a kitchen while you cook will shoot past 80% and settle again. What matters is where a room sits over days and weeks. If it stays above 60% to 65% through the winter, you're heading for condensation and mould. If it's regularly above 70%, it's a problem to fix now. Below about 30%, most people start to notice dry eyes, skin and throats.

What humidity should my house be? The UK thresholds

No UK health body puts a single number on "ideal". The government's damp and mould guidance, NHS advice and the World Health Organization all talk about avoiding persistent dampness rather than hitting a target. The useful numbers come from building standards and research, and they form a ladder:

The Approved Document F limits are design targets for ventilation in new homes, not legal limits for your existing house, but they're a sensible benchmark. Air that averages below 65% over a month shouldn't leave visible mould on the inside of outside walls in a properly heated home.

Is 70% humidity too high in a house?

As an occasional reading, no. As a normal reading, yes. Scotland's building standards say that if a room's average humidity stays at or above 70% for a long time, the humidity at the wall surface will be higher still and is likely to support mould. If your hygrometer shows 70% most mornings in winter, treat it as a warning and start on the fixes below.

80% in a bedroom first thing, or in a bathroom after a shower, is common. 80% in a living room in the afternoon isn't, and it usually means too much moisture going in and not enough getting out.

Relative humidity vs absolute humidity: why heating makes a room "drier"

The humidity on your hygrometer is relative humidity: how close the air is to holding as much water vapour as it can at its current temperature. Warmer air can hold more water, as the Met Office explains, so the same air gives a lower reading when you warm it.

Take outdoor air at 10°C and 80% humidity. Bring it inside and warm it to 20°C without adding a drop of water, and it reads about 42%. Nothing has been removed; the air can simply hold more now. That's why a home with the heating on hard can feel dry in a cold snap, and why a cold, unheated room reads damp even when it isn't producing much moisture.

It works the other way at cold surfaces. Room air at 20°C and 60% humidity has a dew point of about 12°C, so any window, wall or cold corner below about 12°C will collect condensation. BRE once investigated a "leak" that turned out to be just this: 85% humidity at 16°C indoors, a dew point of 13.7°C, and a wall cold spot at 13.5°C to 14.5°C.

Humidity and dew point figures are Aircon Adviser calculations and are approximate.

If your windows are already running with water, our guide on how to stop condensation on windows goes through the causes and fixes in order of cost.

Ideal humidity by room and by season

Living rooms and studies: 40% to 60%. These are the easiest rooms to keep in range.

Bedrooms: there's no separate official figure, so stick to 40% to 60%. Breathing overnight in a closed room pushes humidity up, which is why bedroom windows are often the wettest in the morning. Keep a trickle vent open and a little background heat on.

Babies' rooms: the Lullaby Trust advises a room temperature of 16°C to 20°C and doesn't give a humidity figure. We won't invent one: aim for the same 40% to 60% and focus on temperature.

Bathrooms and kitchens: spikes to 80% or more are normal. The design rules allow up to 85% averaged over a day. Run the extractor fan, keep the door shut, and let the reading fall back afterwards.

Winter: this is when most UK homes run too humid, because windows stay shut and outside surfaces are cold. Steady heating and good ventilation keep it down. The NHS advises heating the rooms you use most to at least 18°C if you can.

Summer: older homes can run humid too. Welsh Government research projects older properties exceeding 60% on roughly half of summer days in the coming decades. Air con's dry mode earns its keep here.

Signs your home is too humid or too dry

The government's damp and mould guidance says damp and mould mainly affect the airways and lungs, with coughs, wheezing, infections and worse asthma and allergies, and that excess moisture also encourages house dust mites. Dry air is usually a comfort problem rather than a health one in UK homes, but research has linked very low humidity with sore and dry throats.

How to measure humidity at home

A hygrometer is the only way to know. Basic digital models cost from about £5 (around £5.40 for a Pro Signal unit at CPC), with others at about £18 (Screwfix) to £25 (Lakeland's Beurer model). App-connected sensors log a history so you can see how humidity changes through the day. Smart heating apps such as tado also show room humidity.

Expect cheap hygrometers to be accurate to around plus or minus 3%. Some retailers quote tighter figures, but treat those as best case.

To get a useful reading:

• Place it at roughly head height, away from radiators, windows, kettles and the outlet of a dehumidifier.

• Give it time to settle after moving it.

• Check it at the same times each day, such as first thing and early evening, for a week before deciding you have a problem.

How to reduce humidity in a house

Work through these in order. The first few cost nothing.

1. Cut the moisture going in. Lids on pans, washing dried in one ventilated room or outside, tumble dryers vented outdoors.

2. Let it out. Keep trickle vents open, run extractor fans during and after cooking and showers, and keep internal doors shut while you do.

3. Heat steadily. Low background heat keeps walls and windows warmer, so less water condenses on them.

4. Use a dehumidifier where the problem is concentrated, especially if you dry clothes indoors. The Centre for Sustainable Energy suggests setting it to keep humidity under 60%.

5. Use air con on dry or cooling mode on mild, muggy days, if you have it.

If humidity stays high despite all of that, there may be a building problem behind it, such as a leak, failed guttering or rising damp, and it's worth getting it looked at.

How to increase humidity in a dry room

This is rarely needed in UK homes, and overdoing it causes more harm than good. Before adding moisture, check you aren't overheating the room: turning the heating down a degree or two often brings the reading back into range on its own. If you do use a humidifier, choose one with a built-in humidistat so it stops at around 50%, keep it clean, and stop using it if condensation appears on the windows.

Does air conditioning reduce humidity?

Yes, in cooling and dry mode. No, in heating mode.

Cooling mode pulls moisture out of the air as it passes over the cold indoor coil, and the water drains away. Mitsubishi Electric notes it only does this well while the room is more than about 2°C above the set temperature. Once the room reaches its target and the compressor slows, moisture removal drops off. An oversized unit that cools the room fast and then switches off will dehumidify poorly.

Dry mode, usually the water-drop symbol on the remote, runs the fan slower and the compressor at reduced speed so the coil stays cold and condenses more water, without cooling the room as hard. GENERAL (formerly Fujitsu General) says it uses less energy than cooling mode, but no manufacturer publishes a dry mode wattage or a litres-per-hour figure. As a guide to what a split can do in cooling mode, LG rates its 2.5kW DUALCOOL Standard Plus at 1.1 litres an hour, but only at its test conditions.

Heating mode removes no moisture. Mitsubishi Electric is explicit that a unit running in heating mode "does not provide dehumidification". Warming the air lowers the relative humidity reading, as explained above, but the water is still there. That's why a reverse-cycle heat pump can make a room feel drier in winter without fixing damp: it helps by keeping surfaces warmer, not by taking water out. You still need to ventilate.

Some brands suggest switching between heat and dry on humid days. On most standard splits you can only run one mode at a time, so check your manual for what yours can do. Our guide to heating with air conditioning covers winter use in more detail.

Dehumidifier or air con: which is better for damp?

For winter damp and drying washing, a dehumidifier. You can move it to the room with the problem, it's designed to run all year, and compressor models are cheap to run. Air con is the better buy if you also want summer cooling and efficient heating; its dry mode is a useful extra for muggy spells, not a replacement for a dehumidifier in January. We compare the two in more depth in does a dehumidifier cool a room?.

Here's what each costs to run at the current price cap:

The models named are examples to show running costs, not recommendations. Rates correct as of October 2026, using the Ofgem price cap for 1 October to 31 December 2026: 26.32p per kWh for electricity, which carries 0% VAT until 31 March 2027. Inverter air conditioners vary their power with the load, so real use will differ.

Compressor dehumidifiers lose much of their output in cold rooms. The Arete Two collects about 5.4 litres a day at 20°C but only about 2 litres at 10°C. For a cold room, a desiccant model keeps working and adds a little warmth, at a higher running cost. You can check your own figures with our running cost calculator.