Is It Cheaper to Heat the Person Rather Than the Whole House?
Is It Cheaper to Heat the Person Rather Than the Whole House?
If one person is sitting in one chair, do we really need to heat twelve thousand litres of air around them?
For many households, this is no longer an academic question.
As autumn turns into winter, people begin looking at the thermostat and wondering what the next energy bill will bring. Some respond by heating the whole house less. Others retreat into one or two rooms, close doors, turn down radiators elsewhere and put on another jumper.
I see this very close to home.
My mother is 95. She worries about the cost of heating an entire house when she spends most of her time in only a few rooms. She turns off radiators in rooms she does not use, closes the doors and keeps the rooms she does occupy at around 18°C.
In fact, that basic idea is very close to current Age UK advice: keep the rooms you use most at a steady, comfortable temperature—around 18°C is suggested—while unused rooms can have their radiators turned off and doors closed.
But it raises a fascinating question:
Instead of heating an entire building to keep one person comfortable, could we heat the person instead?
The answer is yes—but only up to a point.
The smartest approach may be neither "heat everything" nor "heat almost nothing". It is to think of warmth in three layers:
Heat the person. Heat the space being used. Protect the building.
We Don't Actually Heat Just the Air
The opening question about heating thousands of litres of air is deliberately provocative, because there is an important piece of physics behind it.
When we heat a house, we are not simply warming the air.
We are also warming:
- walls;
- floors;
- ceilings;
- furniture;
- windows;
- doors;
- everything else contained in the room.
And at the same time, heat is continually escaping through the building fabric and through ventilation.
That is why warming a cold house takes far more energy than might be suggested by calculating how much energy is required merely to warm its air.
Once the house is warm, the heating system spends much of its time replacing the heat escaping outside.
That immediately suggests an obvious energy-saving principle:
The smaller the area we deliberately keep warm, the less heat we should need to replace.
That does not mean allowing the remainder of the building to become freezing cold. But it does mean questioning whether every bedroom, spare room, hallway and dining room needs to be at precisely the same temperature all day.
Strategy One: Heat the Person
Suppose I am working at a desk, watching television, reading or sitting in an armchair.
My body does not necessarily need the entire room to be 22°C.
What I really want is to feel comfortably warm.
There are some remarkably low-energy ways of achieving that.
Start With Clothing
This sounds almost too obvious to mention, but clothing is insulation.
A warm jumper, cardigan, fleece, thermal layer, thick socks and slippers slow the rate at which heat leaves the body.
And unlike a heating system, a jumper requires no electricity whatsoever once you own it.
There is sometimes a strange modern expectation that we should be able to wander around the house in January wearing the same clothes we would wear in June.
Turning the thermostat up so that we can wear a T-shirt indoors during winter is not particularly logical.
That does not mean sitting indoors wearing a coat and gloves.
It simply means recognising that personal insulation can be part of an intelligent heating strategy.
The Heated Throw May Be One of the Most Interesting Energy-Saving Devices
A heated throw changes the equation considerably.
An ordinary electric blanket is typically around 80–120W according to Electrical Safety First. By comparison, a conventional portable electric radiator or fan heater may typically draw around 2,000–3,000W.
That is an enormous difference.
Consider a nominal 100W heated throw.
Used for four hours:
100W x 4 hours = 400Wh
or:
0.4kWh
If your electricity costs 25p per kWh, that would be approximately:
0.4 x 25p = 10p
The exact figure will depend on your tariff, the blanket's power rating and how its thermostat cycles, but the scale of the difference is the important point.
A heated throw is warming one person, not several tonnes of building materials.
That makes it potentially extremely effective when somebody is sitting still for a long period.
Reading.
Watching television.
Working at a computer.
Knitting.
Studying.
Or simply relaxing in the evening.
An Electric Blanket Can Do Something Similar at Night
Heating an entire bedroom throughout the night simply to maintain a warm bed is another situation worth questioning.
An electric blanket can pre-warm the bed using a relatively small amount of energy.
However, electrical safety matters.
Electrical Safety First recommends checking blankets regularly for wear or damage, following the manufacturer's instructions, using over-blankets and under-blankets only as intended and never using an electric blanket while it is folded or badly creased. It also advises never combining an electric blanket and hot-water bottle.
The London Fire Brigade similarly advises checking for damaged fabric, exposed wiring, damaged leads or overheating connectors and following the manufacturer's instructions regarding overnight use.
So "heat the person" should never translate into improvising with questionable old electrical equipment.
Don't Forget the Old-Fashioned Hot-Water Bottle
There is another remarkably simple personal heating device.
The hot-water bottle.
Heating a relatively small quantity of water and placing it beneath a blanket can provide warmth for quite some time.
Again, sensible precautions matter, and a hot-water bottle should not be used together with an electric blanket.
Sometimes old technology remains useful precisely because it is so simple.
Strategy Two: Heat the Room You Are Actually Using
Personal heating is excellent while somebody is stationary.
But we still need to get up.
Cook.
Walk to the bathroom.
Move around the house.
Work at a table.
Welcome visitors.
That is where zoned heating becomes particularly interesting.
My mother's strategy is a good example.
She does not try to maintain every room at the same temperature.
She heats the rooms she actually uses, closes doors and reduces or switches off heating elsewhere.
Modern thermostatic radiator valves make this much easier.
Energy Saving Trust recommends setting TRVs to the lowest level that keeps each room comfortable and specifically suggests turning them down in rooms that are used less frequently.
That could mean:
Living room: comfortably warm
Kitchen: heated while being used
Bedroom: comfortable around bedtime and morning
Spare bedroom: substantially cooler
Dining room: heated only when required
Hallway: cooler again
Suddenly we are no longer treating the entire house as one giant thermal zone.
Close the Door—It Really Does Matter
One of the simplest heating controls in existence has no batteries, Wi-Fi connection or smartphone application.
It is called a door.
If one room is deliberately being kept warm while the adjoining room is cooler, leaving the door open allows air to circulate and temperatures to equalise.
Closing it helps maintain the temperature difference.
This is particularly useful when somebody spends much of the day in one living room.
Close the door.
Close curtains after dark.
Deal with significant draughts.
Use the room rather than attempting to maintain identical temperatures throughout the house.
Sometimes effective energy saving requires very little technology.
But Turning Every Other Radiator Off Has Limits
This is where the argument becomes more complicated.
If an unused bedroom becomes very cold, its walls, windows and other surfaces become cold too.
Moisture produced elsewhere in the home can migrate into that room.
When warm, moisture-laden air encounters a sufficiently cold surface, condensation can form.
Then we may create an entirely different problem:
damp and mould.
Energy Saving Trust warns that rooms where heating is switched off or kept very low during colder weather can be more prone to damp problems and recommends appropriate ventilation and, where necessary, some heating.
So we should distinguish between:
a cooler room
and
an abandoned, freezing room.
They are not necessarily the same thing.
Ventilation Is Still Necessary
There is another temptation when energy is expensive.
Seal everything.
Never open a window.
Block every vent.
Keep every possible molecule of warm air indoors.
Unfortunately, people generate water vapour.
So do:
- showers;
- baths;
- cooking;
- drying clothes;
- washing up;
- breathing.
That moisture has to go somewhere.
Extractor fans in kitchens and bathrooms can therefore be extremely important.
Energy Saving Trust recommends using extractors during activities such as cooking and showering and continuing to ventilate afterwards.
The objective isn't to create an airtight damp box.
It is to ventilate intelligently without needlessly throwing away large quantities of heat.
The Portable Electric Heater Is a Different Proposition
There is an important distinction between a 100W heated throw and a 2kW electric heater.
People sometimes group the two together as "electric heating".
But economically they are completely different.
A 2kW fan heater running for four hours consumes:
2kW x 4 hours = 8kWh
A 100W throw running for four hours consumes:
0.1kW x 4 hours = 0.4kWh
That is a factor of twenty.
So although a portable heater can make sense for quickly warming a small occupied room, it does not automatically follow that replacing central heating with plug-in electric heaters will save money.
The real question is always:
What are we heating, for how long, and with what technology?
Heat Pumps Add Another Interesting Twist
This becomes even more complicated in homes with heat pumps.
A resistance heater effectively turns one unit of electrical energy into roughly one unit of heat.
A heat pump moves heat from outside to inside and can deliver several units of heat for each unit of electricity consumed under suitable conditions.
That means switching off an efficient heat pump and replacing it with several portable resistance heaters may sometimes be a false economy.
Zoning and lower room temperatures may still be useful—but the heating system matters.
There is rarely one universal answer.
Perhaps We Should Think About Comfort Rather Than Temperature
Two people can sit in the same 19°C room and feel completely different.
One is moving around cooking dinner.
The other is sitting motionless reading.
The first might feel perfectly warm.
The second may feel cold.
That tells us something important.
Thermostat temperature is only part of comfort.
Clothing matters.
Air movement matters.
Activity matters.
Cold surfaces matter.
Personal preference matters.
Radiant warmth matters.
That is why putting a heated throw around someone sitting still can sometimes make a greater difference to perceived comfort than increasing the thermostat by another degree.
For Older and Vulnerable People, Cost Saving Must Have a Boundary
This is the part of the argument that concerns me most.
I understand why my 95-year-old mother worries about heating an entire house.
I suspect many thousands of older people have precisely the same concern.
But there comes a point where saving another few pounds is not worth allowing someone to become seriously cold.
Age UK currently suggests a steady, comfortable temperature in the rooms older people use most, usually around 18°C, and stresses the importance of staying warm as we get older.
That seems a much more sensible philosophy than either extreme.
Not:
"Heat every room to 22°C regardless of whether anyone uses it."
But equally not:
"Turn everything off and simply put another blanket on."
There is a middle course.
A Practical Three-Layer Winter Strategy
I think this is the approach that makes the most sense.
1. Heat the person
Use sensible clothing, warm socks, slippers, blankets and, where appropriate, safely used heated throws or electric blankets.
2. Heat the occupied space
Keep the room being used at a comfortable temperature. Use thermostatic radiator valves, schedules and closed doors to avoid unnecessarily heating every part of the house equally.
3. Protect the building
Do not allow unused areas to become so cold and poorly ventilated that condensation, damp or mould become problems.
That is much more sophisticated than simply asking:
"Should the heating be on or off?"
Do the One-Chair Test
Here is a useful experiment for this winter.
Next time you are sitting in one chair watching television in a large house, look around.
How many rooms are being heated?
How many of those rooms contain anybody?
Could one unused room be reduced slightly?
Could a door be closed?
Could curtains be drawn?
Could a draught be fixed?
Would another layer of clothing make you perfectly comfortable?
Would a low-powered heated throw allow the room thermostat to be turned down slightly without making you uncomfortable?
Don't make ten changes at once.
Try one.
See whether you notice the difference.
Then check what happens to energy consumption.
That turns energy saving from guesswork into an experiment.
The Greenest Heat May Be the Heat You Don't Need to Produce
There is a broader environmental lesson here too.
We often imagine going green means buying a new heating system, smart thermostat, solar panels or expensive insulation.
Those things can certainly matter.
But efficiency also comes from asking a much simpler question:
What am I actually trying to achieve?
We don't fundamentally want warm houses.
We want warm people living in healthy houses.
Those are not quite the same objective.
If one person is sitting in one chair, there may be little point maintaining every unused room at exactly the same temperature.
But nor should fear of the bill force someone—particularly an older or vulnerable person—to live in an uncomfortably cold home.
The sensible answer sits between the extremes.
Heat the person where you can.
Heat the rooms you use.
Turn down those you don't.
Control draughts.
Ventilate where moisture is produced.
And never save energy by making the home unsafe or unhealthy.
Perhaps the future of domestic heating isn't simply about finding a cheaper way to heat an entire house.
Perhaps it begins by asking:
Who actually needs to be warm—and where are they sitting?
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