Gas vs Electric Geyser: What Hot Water Actually Costs in Winter
A tank geyser left on all winter spends more energy keeping water hot between showers than it does heating the water you use. Here is the arithmetic, by fuel, per month.
Every Pakistani winter brings the same argument. One side says the gas geyser is practically free; the other says the gas bill trebles in December and something must be causing it. Both are describing the same appliance.
The confusion exists because a geyser has two separate energy costs, and almost every discussion collapses them into one. There is the energy that ends up in the water you actually use, and there is the energy spent keeping a tank full of water hot for the twenty-three hours a day nobody is showering. The second is invisible, and in an old geyser it is the bigger number.
First, the physics — then the rupees
Heating water takes a fixed, knowable amount of energy. Raising one litre by one degree Celsius takes 4.186 kilojoules, so:
Energy (kWh) = litres × temperature rise × 4.186 ÷ 3,600
In a Pakistani winter, mains water arrives at roughly 15°C and a comfortable shower is about 40°C — a 25°C rise. A typical bucket bath uses about 35 litres; a short shower, about 50.
| Use | Litres | Energy needed |
|---|---|---|
| One bucket bath | 35 | 1.02 kWh |
| One short shower | 50 | 1.45 kWh |
| 100 litres | 100 | 2.91 kWh |
That is the energy that must be delivered into the water. What you pay depends on the fuel that delivers it and how much is wasted on the way.
Cost per 100 litres, by fuel
Electric elements are close to 100% efficient — essentially all the electricity becomes heat in the water. Gas burners are not: a good deal of the flame's heat goes up the flue, and 65% efficiency is a fair figure for a domestic tank geyser.
| Method | Efficiency | Energy bought per 100 l | Unit price | Cost per 100 l |
|---|---|---|---|---|
| Gas geyser (protected slab) | 65% | 4.48 kWh | ~Rs 4/kWh equiv. | Rs 18 |
| Gas geyser (higher slab) | 65% | 4.48 kWh | ~Rs 22/kWh equiv. | Rs 99 |
| Electric, protected tariff | ~100% | 2.91 kWh | Rs 10/unit | Rs 29 |
| Electric, unprotected | ~100% | 2.91 kWh | Rs 35/unit | Rs 102 |
| Electric, top slab | ~100% | 2.91 kWh | Rs 48/unit | Rs 140 |
| LPG cylinder | 65% | 4.48 kWh | ~Rs 30/kWh equiv. | Rs 134 |
The headline everyone expects — gas is cheaper — is only true on the protected slab. A household in a higher gas slab paying an unprotected electricity tariff is choosing between Rs 99 and Rs 102 per hundred litres, which is no choice at all.
The standing loss nobody counts
Now the part that explains the December bill. A tank geyser does not heat water once and stop. It holds 30–50 litres at temperature and reheats every time that water cools, all day and all night, whether or not anyone uses it.
An older, poorly insulated tank geyser loses roughly 1.5–2.5 kWh a day to standing loss. Compare that against a family's actual usage:
| Household of 4, per day | Energy into water | Standing loss (old tank, always on) | Waste share |
|---|---|---|---|
| 4 bucket baths | 4.08 kWh | 2.00 kWh | 33% |
| 2 bucket baths | 2.04 kWh | 2.00 kWh | 50% |
| Weekend, nobody home | 0 kWh | 2.00 kWh | 100% |
A small household running an always-on tank geyser is spending as much on keeping water hot as on using it. Over a 120-day winter that is 240 kWh burned for nothing — Rs 8,400 at Rs 35 a unit.
What to actually do about it
| Change | What it saves over a 120-day winter | Cost |
|---|---|---|
| Switch the geyser off between uses (or fit a timer) | Up to 240 kWh — Rs 4,300–8,400 | Rs 0, or ~Rs 3,000 for a timer |
| Insulating jacket on an old tank | ~90 kWh — Rs 1,600–3,100 | Rs 2,500–4,000 |
| Lower the thermostat to 50°C | ~40 kWh — Rs 700–1,400 | Rs 0 |
| Bucket instead of shower | ~0.43 kWh per wash | Rs 0 |
| Instant geyser for a 1–2 person home | Removes standing loss entirely | Rs 15,000–35,000 |
The first row is free and is the biggest single item on the list. That is unusual enough to be worth repeating: the best available saving here costs nothing and is undone by nothing more than the habit of leaving a switch on.
When an instant geyser is the right answer
Instant (tankless) units heat water only while it flows, so standing loss is zero. That makes them clearly right for one or two people, or for a kitchen tap used briefly several times a day.
They are the wrong answer for a family of five all bathing between 7 and 8am: an instant unit is limited by its flow rate, and an electric one draws a lot of current while running, which matters if your wiring or your supply is marginal. A tank geyser plus a timer usually beats an instant unit for a large household.
Standing loss is the same phenomenon that makes an idle appliance expensive across the board — the same logic that drives the fridge, the AC and the rest of the bill is worked through in how to cut your electricity bill, and the per-hour method here is the one used in what it costs to run an AC.
Frequently asked questions
Is a gas geyser cheaper than an electric one in Pakistan?
On the protected gas slab, clearly yes — roughly Rs 18 against Rs 29 per hundred litres. On a higher gas slab against an unprotected electricity tariff the two are effectively level, at around Rs 99 versus Rs 102.
Should I turn my geyser off when not in use?
Yes, and it is the single largest saving available. An always-on old tank geyser wastes 1.5–2.5 kWh a day to standing loss — up to Rs 8,400 across a winter for a household that uses hot water twice a day.
How much electricity does a geyser use per bath?
About 1.02 kWh for a 35-litre bucket bath and 1.45 kWh for a 50-litre shower, assuming water is raised from 15°C to 40°C. Standing loss is on top of that.
Are instant geysers cheaper to run?
They eliminate standing loss, which makes them cheaper for one or two people. For a large family bathing at the same time, a tank geyser on a timer is usually the better choice because instant units are limited by flow rate.
Does an insulating jacket on a geyser work?
Yes, on an older tank — it typically cuts standing loss by around a third and pays for itself within a winter or two. On a modern, well-insulated tank the gain is much smaller.
Sources and method. Energy figures are computed from first principles using 4.186 kJ per litre per °C and a 15°C→40°C rise; assumed efficiencies are ~100% for electric elements and 65% for domestic gas geysers. Gas costs are expressed as a rupees-per-kWh-equivalent to allow comparison and are approximations of protected and higher domestic slabs as at August 2026 — gas and electricity tariffs in Pakistan change with OGRA and NEPRA determinations, so substitute your own bill's rates. Standing-loss figures of 1.5–2.5 kWh/day are typical ranges for older domestic tank geysers, not a measurement of any specific model.
