Where the savings actually live in a typical home

Step 1: Read your last 12 months of energy bills

Before talking about insulation, heat pumps, or solar, you need one number: how many kWh you actually use in a year.

Pull up your last 12 months of energy bills. If you have both gas and electricity, you’ll need both. Ignore the currency for now; focus on kWh totals.

Walk through this once, then you’ll never unsee it.

1. 1

   For each bill, find the “usage” section

   Note the kWh figure, not the estimated annual cost.
2. 2

   Add up 12 months for each fuel separately (gas, electricity, oil, etc

   ). A spreadsheet or notes app is enough.
3. 3

   Divide the annual kWh by 12 to get an average month

   This helps when you sanity-check later.

If you can’t get 12 months, use what you have and scale cautiously. Six winter-heavy months will overstate annual use; six mild months will understate it. If your utility shows an annual kWh bar chart, copy that instead.

Think of your bills as a slow, noisy meter of your house’s physics. They don’t care about marketing or good intentions; they just report how many kilowatt-hours vanished into heat, hot water, and devices. Once you see that number clearly, a lot of “green” advice stops making sense, and the sensible upgrades almost pick themselves.

Sanity check: in many temperate-climate homes, annual electricity is 2,000-5,000 kWh, and gas/heat is 8,000-20,000 kWh. If you’re an order of magnitude outside that, re-check readings and units.

Step 2: Map usage into the big three: heat, hot water, plug load

You don’t need a full engineering model. A rough split is enough to aim correctly.

Residential energy typically falls into three big buckets:

Space heating

Keeping the air and surfaces warm. Radiators, underfloor heating, warm-air systems, heat pumps, furnaces.

Hot water

Showers, baths, taps, dishwasher (partly), washing machine (if it heats with your fuel).

Plug and appliance load

Everything electric that is not heating water or space: lights, fridge, cooking, electronics, chargers.

Rule-of-thumb in a gas-heated home:

In an all-electric home with resistive heating, space and water heat may dominate electricity use (often 50-70%). With a heat pump, heating kWh fall, but still usually beat plug loads.

To get a first split:

1. 1
   If you heat with gas or oil, assume 80-90% of that fuel is heat and hot water, the rest for cooking if applicable.
2. 2
   Assume 70-80% of that heating fuel is space heating and 20-30% is hot water, unless you take many long hot showers.
3. 3
   Assume most of your electricity (except for electric heating, hot-water cylinders, or underfloor) is plug load.

Write down the rough kWh per bucket. You now have a crude pie chart of where your money and CO2 go.

A first attempt: your 20-minute mini-audit

Now convert that information into a concrete picture of your home.

Set a timer for 20 minutes and do this once, start to finish.

1. 1
   Summarise your year. On one sheet of paper (or a note), write: annual kWh for each fuel, plus your rough space heat / hot water / plug-load split.
2. 2
   Walk the house once. As you walk, ask: what’s using energy right now? Radiators warm? Cylinder hot? Lights and devices on in empty rooms?
3. 3
   Mark obvious candidates. Next to each bucket on your sheet, write 2-3 concrete levers. For example, under space heating: “radiators hot in unused room”, “thin loft insulation”, “big draught under front door.”

Good feedback from this first pass looks like this:

• You can point to one dominant category (“space heating is ~65% of our use”).
• You’ve written at least one behaviour lever (“heating on 22°C all day”) and one fabric lever (“loft is barely insulated”).

Poor feedback looks like this:

• Your notes focus on phone chargers, LED bulbs, and turning off the TV light, even though your heating kWh dwarf everything else.

If your first attempt looks poor, don’t worry. The rest of this guide exists to correct that instinct and give you better levers.

What actually moves the bill: ranked interventions with numbers

Let’s turn vague ideas into a crude league table. Numbers are indicative for a “typical” temperate-climate home using ~12,000 kWh/year for heat and hot water and ~3,000 kWh/year for electricity.

Use this table to get direction and order, not a precise quote:

The pattern: behaviour and cheap fabric changes give the fastest, safest returns. Big equipment (heat pumps, solar, batteries) can be excellent, but only once the building is reasonably efficient and your usage pattern suits them.

Nothing in this table requires belief. It’s just “kWh saved per year” divided into “money and hassle required once.”

Behaviour changes: free savings that genuinely add up

Most people underweight behaviour because it sounds trivial. The maths says otherwise, especially for heating and hot water.

Thermostat maths: in many climates, heat loss is roughly proportional to the temperature difference between indoors and outdoors. Drop your setpoint from 21°C to 19-20°C and cut some “empty house” hours, and you commonly save 5-15% of heating energy with zero hardware.

Do one concrete 7-day experiment:

1. 1

   Pick a new, slightly lower heating schedule for a week

   For example, set 19-20°C when home, lower when asleep or out, and reduce total “on” hours.
2. 2
   During that week, note when rooms actually feel uncomfortably cold vs just cooler than habit.
3. 3

   After a week, adjust room-by-room

   perhaps bedrooms can run cooler, living spaces modestly warmer, with doors shut.

Good feedback: you find a schedule where most of the time the house is fine, a few times you add a jumper, and your heating runtime clearly dropped (radiators hot for fewer hours, or lower boiler/heat-pump activity).

Poor feedback: you set everything to 17°C, the household rebels, and you snap back to 23°C all day. That’s not failure; it’s a bad step size. Next retry, nudge by 0.5-1°C, not 3-4°C.

Apply the same logic to hot water. If everyone takes 12-minute showers, target 7-8 minutes. Over a year, that’s non-trivial kWh and water, especially with electric or gas combi systems.

Draught-proofing and insulation: fixing the thermal envelope

Once behaviour is sensible, the next biggest, relatively cheap wins are in your thermal envelope, how fast heat leaks out.

Draught-proofing is about uncontrolled air leaks: gaps around doors, loft hatches, old letterboxes, unsealed floorboards by external walls. You feel them as cold streaks or moving air on a windy day. Stopping these with seals, brushes, and basic joinery often gets you 5-15% heating savings for a low spend.

Insulation is about U-value, how easily heat flows through roofs, walls, and floors. Many older homes have inadequate loft insulation; topping it up to a modern standard is inexpensive and can cut 10-20% of heating use. Cavity wall insulation (where appropriate and well-installed) can be similar.

Don’t over-prioritise windows. Replacing all glazing mainly makes sense when they’re failing anyway (rot, leaks, safety). The savings from moving from decent double-glazing to top-end triple are usually modest compared with fixing a bare loft or uninsulated cavity.

Heating controls and smart thermostats: what they really do

Controls don’t create efficiency out of thin air; they reduce overheating and needless runtime.

A programmable or “smart” thermostat, used properly, automates what you could do manually with discipline: lower temperatures overnight and when you’re out, and avoid heating unused rooms. In practice, studies and field data often land in the 5-15% heating savings range.

The key is configuration:

• If you install a fancy thermostat and leave it at 22-23°C 24/7, savings will be near zero.
• If you combine a moderate setpoint, clear schedules, and room-level zoning (TRVs, zone valves), you capture most of the potential.

When you evaluate advice or marketing, translate it into your numbers: “If this saves 10% of my 10,000 kWh heating use, that’s 1,000 kWh/year. At my tariff, is that worth the cost and any subscription?”

Heat pumps vs boilers: plain-language tradeoffs

Heat pumps are efficient because they move heat rather than create it. A well-designed system can deliver 2.5-4 units of heat per unit of electricity (manufacturer spec sheets and field data often call this COP or seasonal performance factor).

If your home currently burns 12,000 kWh/year of gas for heating, a heat pump with a seasonal COP of 3 might need only ~4,000 kWh of electricity to deliver the same heat. Whether that saves money depends on your local gas vs electricity prices and tariffs.

Where heat pumps make the most sense:

• Your home already has decent insulation and draught-proofing.
• You can run low-temperature radiators or underfloor heating (bigger emitters, lower flow temps).
• You expect to stay for many years, so a 7-15+ year payback is acceptable.
• You care about carbon as well as cost; even with current grid mixes (often ~300-500 g CO2e/kWh), a COP of 3 usually beats burning gas per kWh of delivered heat, per IEA and IPCC analyses.

Where a new efficient boiler or furnace may be more rational:

• The envelope is poor and you’re not fixing it soon, so a heat pump would have to work too hard at high flow temperatures.
• Your heat demand is modest (e.g., small flat), so even big relative savings don’t add up to much absolute kWh.

Treat heat pumps as part of a whole-system upgrade, not a magic box that fixes a leaky shell.

Solar PV (and batteries) vs just using less

Solar PV shifts where your electricity comes from, not how much you need. It can be excellent, especially on sunny, high-usage homes, but in pure kWh avoided from the grid per unit of money, basic efficiency often wins first.

A rough picture:

• A 3-4 kW solar PV system might generate 2,500-4,000 kWh/year, depending on location and roof orientation.
• If your household uses 3,000 kWh/year, this can cover a large fraction of your electricity, especially if you shift usage into sunny hours.
• Simple payback often sits in the 8-15 year range without subsidies, depending on costs and tariffs.

Batteries mainly help you use more of your own solar when you’re not home during the day, and sometimes arbitrage time-of-use tariffs. They rarely beat fabric and behaviour in payback.

If you haven’t yet:

then solar is an expensive way of compensating for waste. Do the cheap kWh first.

Things that look impactful but usually aren’t

Some actions feel very “green” but move little on either your bill or emissions, especially compared with heating.

Swapping every visible item for a “sustainable” alternative tends to fall into this category: new eco-branded kitchenware, reusable gadgets you rarely use, or minor packaging changes. On the energy side, the usual suspects are:

• Over-focusing on phone chargers and standby on modern devices. These are typically a few kWh/year each, not thousands.
• Replacing OK double-glazed windows mainly “for efficiency” while leaving an uninsulated loft above.
• Buying expensive smart-home gadgets whose only efficiency feature is turning off things you could already switch off.

There is nothing wrong with doing these if you enjoy them and can afford them. Just don’t confuse them with the heavy lifters of home energy savings: envelope, heat, and water.

Putting it together: a practical order of operations

You now have enough to build a rational sequence for your home.

In most temperate-climate homes, ordered by cost-effectiveness and generality, the ladder looks like this:

1. 1
   Measure and understand: 12-month kWh by fuel, rough split into heat/hot water/plug.
2. 2
   Behaviour and controls: thermostat setpoints and schedules, hot water habits, turning off or timing obvious loads.
3. 3
   Draught-proofing and cheap insulation: doors, loft hatch, obvious gaps, attic top-up.
4. 4
   Targeted fabric upgrades: cavity walls if suitable, floor insulation if accessible, fixing damp/air-leak routes.
5. 5
   Smart controls and zoning: thermostats, TRVs, scheduling poorly controlled areas.
6. 6
   Major kit changes: heat pumps vs new boiler, solar PV, possibly batteries, driven by your actual loads and roof.

For your next 12 months, you don’t need to do everything. Pick one or two levers per rung that your mini-audit flagged, then instrument them. For example, note boiler run hours this month vs last after schedule changes, or compare winter kWh after loft insulation is installed, normalising roughly for temperature.

This turns “being greener” from a vague feeling into a small, ongoing engineering project with a clear scoreboard: kWh per year per square metre of house, and comfort maintained.