Outside Temperature Drop Winter 2025

We are currently experiencing a significant drop in outside temperatures, and as a result you will now need to heat your property more frequently than in previous weeks.

Under the terms of your tenancy agreement, and in line with Environmental Health recommendations, the property must be maintained at a minimum temperature of 13°C at all times. This baseline temperature helps keep the property dry and protects it against issues associated with cold and damp.

For comfort, I recommend setting your heating to around 18°C as a minimum. You may still require additional layers at this temperature, and many people prefer to maintain their home at approximately 22°C. While you may turn down the radiators in rooms you use infrequently, you should not switch any radiators off completely, as all areas of the property require heat regardless of how often they are used.

I also recommend that your heating is controlled by the timer. On mild winter days, the property will typically require at least two hours of heating. On colder days such as today, the focus should be on maintaining a stable internal temperature rather than relying on short bursts of heating.

If the property will be vacant for any period, please ensure you have sufficient gas credit or oil to maintain the heating whilst you are away. The heating should either be set to maintain a minimum temperature or scheduled to activate periodically throughout the day.

To ensure your heating system operates efficiently:

• All radiator valves should be open, and the radiators should heat fully.
• Radiators that are warm at the bottom but cold at the top may contain trapped air and may require bleeding.
• After bleeding a radiator, you must check and top up the boiler’s pressure, as bleeding reduces system pressure.
• Avoid obstructing radiators with furniture or covering them with clothing, towels or curtains. Curtains should be tucked behind the radiator when closed, not draped over the front.
• Allowing the property to become cold will result in longer and more expensive heating cycles when you attempt to warm it again. It is generally more efficient to maintain a consistent level of heat.
• Your boiler must also be run at least once every two weeks for approximately 15 minutes to prevent issues caused by inactivity, which can lead to component degradation and eventual failure. The landlord is responsible for servicing the boiler, but you are responsible for operating it regularly.

Condensation and Ventilation

As the outside temperature drops, condensation inside the property becomes more likely. The colder it is outside—and the more heat used inside—the more condensation will form. Each room should be aired for 5–15 minutes per day to release moisture from the indoor air.

If you work or study from home, ventilation becomes even more important. The more time you spend in a room, the more moisture you generate simply by breathing.

Moisture Generated by Occupants

A couple can exhale and perspire between 1 and 2 litres of moisture overnight in a closed bedroom. This is a major source of humidity and condensation.

General estimates for an eight-hour sleep period:

Per person: 0.5–1 litre of moisture released through breathing and perspiration.

Per couple: 1–2 litres combined.

One person exhales approximately 130g of water vapour overnight, increasing to around 400g over 24 hours, even without additional activity.

When a bedroom door and window are closed overnight, this moisture becomes trapped. As the room cools—especially near windows—the air reaches saturation, and the moisture condenses on cooler surfaces such as glass and external walls. Over time, this can lead to dampness, mould growth and associated health concerns. Proper ventilation is the most effective way to prevent this.

Implications for Single and Double Occupancy Rooms

In non-HMO properties where two people share a bedroom, up to 2 litres of water can be added to the air overnight, not including moisture from:

• drying clothes,
• cooking,
• bathing, or
• condensation already on the windows.

This is why daily ventilation is essential.

In HMO properties, all bedrooms are strictly single occupancy. Even with one person, around 1 litre of moisture can be released into the air overnight. If you work or study in your bedroom during the day as well, these moisture levels will likely double.