Spend first where the house leaks money.

A modern efficient unit uses roughly 250–350 kWh a year — about $40 to $56 at the US average rate. Anything over 500 kWh points to an old or failing unit, and a twenty-year-old fridge can easily double the modern figure, which is why it is usually the highest-value replacement in a house.

It is the fraction of the time the compressor actually runs, typically 30–50%. Multiplying nameplate watts by 24 hours assumes the compressor never stops, which would overstate consumption two to three times. A rising duty cycle over the years — from failing door seals, dust-clogged coils or a warm kitchen — is often the first sign a fridge is on its way out.

Only if the payback is comfortably shorter than the remaining life, and even then the new unit carries embodied manufacturing carbon that takes years of operational saving to offset. Replacing at end of life is where the economics and the carbon both work cleanly. The exception is genuinely old always-on equipment, where the running cost gap is large enough to justify early replacement.

Very little with modern hardware. Ten chargers drawing half a watt each come to about 44 kWh a year — around $7. The advice made much more sense when power supplies were less efficient, and it persists mostly because it is an easy action to recommend. It is not wrong, it is just small.

The large ones. Set-top boxes and DVRs, game consoles left in instant-on mode, older AV receivers and some smart speakers can each draw ten to twenty watts continuously — one of those outweighs a drawer full of phone chargers. A switched power strip on the entertainment centre captures most of the available saving.

Roughly 80–85% for the same light output: a 60 W incandescent is replaced by an 8–10 W LED. Run five hours a day, that is about 90 kWh a year saved per fixture — around $15 — and the LED lasts long enough that the replacement cost largely disappears too.

A modest amount on lighting, and the effect on cooling load cuts both ways: you avoid the lamp’s waste heat, but a sunlit window admits considerably more heat than the lamp ever produced. In a cooled climate, daylight through unshaded glass can cost more in air conditioning than it saves in lighting.

In a typical US home, space heating and cooling dominate, followed by water heating, then refrigeration and lighting, with electronics and everything else making up the remainder. Any serious reduction plan starts with the thermal envelope and the HVAC system, not with the plug loads.

About 0.386 kg on the US national average grid, but the spread by region is enormous — a coal-heavy grid can be triple a hydro or nuclear one. That is why the same appliance change saves very different amounts of carbon depending on where you live, even though the dollar saving is similar.

The commonly cited figure is around 10,000 sheets, and it is used here for that reason, but it is a rough communication device rather than a measurement. Yield varies hugely with species, tree size and mill process, and most office paper already contains recycled fibre, which breaks the tree-count framing entirely.

Replacing an old refrigerator, if you have one — it is the largest continuously running load in most homes and the efficiency gap between a 2005 unit and a current one is dramatic. Lighting comes next if you still have incandescent or halogen fixtures. Standby loads are last, by a wide margin.