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Mon Dec 1, 2014

In the third and final part of our comfort in the home blog series we’re looking at comfort temperature, heat perception and why just three degrees can make all the difference.

How hot is too hot?

This depends entirely on the individual and their situation.  

Visualise yourself lounging in the garden with a glass of something refreshing in a balmy 27°C heat – does that sound like your idea of heaven?

Let’s change the situation – so now you’re trying to sleep, you’ve got an early meeting and it’s still the 27°C you were enjoying earlier – only now you’re in purgatory!

Thermal comfort levels are particularly important at night. Environmental Design, Guide A* advises that bedrooms should be 23°C or lower to have no effect on quality of sleep.

Research carried out by CIBSE & Arup** tells us that 3°C is enough to turn us from comfortably ‘warm’ at 25°C to uncomfortably ‘hot’ at 28°C. It seems amazing that 3°C can have such an impact on our comfort levels.

As examined in part 2, humidity plays a major role. So, in order to achieve comfort, we also need to pay particular attention to the effect of humidity on perceived vs. actual temperature. The heat index tells us that this additional 3°C may just be perceived heat due to humidity levels.

How can we tackle this?

As discussed in our latest publication on overheating, climate change means that homes in the UK are likely to become increasingly uncomfortable in summer unless other approaches to cooling are used. This is where the ventilation strategy in airtight, low-energy homes can provide additional benefit.

For example, one method would be to select an ERV instead of an HRV – that way some of that excess humidity can be kept outside, where it belongs.

By reducing the humidity levels in the home you can also reduce the perceived air temperature and add to the comfort of the occupants. And the benefit will be felt throughout the entire home with none of the draughts or increased energy usage associated with other cooling methods.

So what is the ideal comfort temperature for humans?

For scientific work, room temperature*** (the range in which air feels neither hot nor cold) is taken to be between 20 to 26°C and the Lansing State Journal, in March 1997, identified 72°F (22.2°C) as the ideal comfort temperature.

The simplified scientific reason is that the human body needs to transfer its excess heat energy into the air in order to maintain our body temperature of 37°C. If we aren’t surrounded by cooler air, our body temperature would continue to rise as we went about our daily tasks, with potentially fatal results.

If two objects touch, the rate at which energy/heat is transferred from one to the other depends on the temperature difference between them. At 22.2°C, the air is the perfect temperature to receive our flow of body heat at the same rate that we generate it.

How do we achieve the ideal 22.2°C?

Imagine yourself leaving work to drive home on a summer’s evening where your car has been sat baking in the sun all day. We’ve all been there – you open the door and feel the heat hit you like a blast furnace. Every surface seems to be made of molten lava. Even the feel of the seatbelt is unbearable! The first thing we do is whack the air conditioner’s thermostat down to ‘low’ and the fans up to ‘high’. For a few minutes, it’s sheer bliss – but just for a few minutes.


Once the air temperature has reduced to ‘low’ (usually 16°C) it has gone way past our ideal comfort level into the realms of cold and draughty. You spend the rest of the journey alternating between turning the air con on and off – never quite reaching comfort.

So, what does this mean for your home?

16°C is too cold to be considered comfortable yet this is what air con units give us. By choosing air conditioning you will just be taking the car scenario and repeating in your home, trying to balance the optimum comfort temperature but never quite achieving it and also costing you time and money.

Specifying an alternative comfort cooling technology alongside your ventilation strategy means that you can get it right first time and maintain comfort through the year.  

*Chartered Institution of Building Services Engineers (CIBSE). Environmental design, Guide A. London, CIBSE, 2006.

** Hacker, JN, Belcher, SE & Connell, RK (2005). Beating the heat: keeping buildings cool in a warming climate. UKCIP Briefing Report. UKCIP, Oxford.

*** (source:

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