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Water Heater Cost Calculator
Calculates what heating your hot water costs a month, separates the standing loss from the useful heat, and compares five heater types.
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At a 45°C rise. Older tanks lose 2–3
Enter your figures and press Calculate.
In short
Water Heater Cost Calculator is a free online tool on inputtesthub.com that calculates what heating your hot water costs a month, separates the standing loss from the useful heat, and compares five heater types. It needs no account, no download and no payment, and there is no daily usage limit. Everything is processed inside your own browser, so the data you paste is never uploaded to a server.
How to use the Water Heater Cost Calculator
- Enter your figures in the input fields.
- The result updates as you type, together with the full working.
- Check the breakdown table to see exactly how the number was reached.
About the Water Heater Cost Calculator
The Water Heater Cost Calculator calculates what heating your hot water costs a month, separates the standing loss from the useful heat, and compares five heater types. It runs as plain JavaScript inside the page, which means there is no upload step, no queue and no size limit imposed by a server — the only limit is your own device.
What people use it for
- Deciding whether a tankless heater would pay for itself.
- Seeing what the thermostat setting actually costs.
- Comparing gas against electric against a heat pump on your own prices.
Details
| Electric resistance | ≈ 98% efficient |
|---|---|
| Gas storage | ≈ 70% |
| Heat pump | ≈ 300% — it moves heat, not makes it |
| Standing loss, modern tank | 1–2 kWh a day |
| Minimum safe storage | 60°C, for legionella |
The maths behind it
This tool uses useful heat = litres × 4.186 × temperature rise ÷ 3,600 kWh. Divide by the heater efficiency for what it draws, then add the standing loss, which scales with tank size and with how far above the room the water is held. Every intermediate value is shown on screen, so the result can be checked by hand.
Standing loss is the entire difference between a tank and an instant heater and it is the number most likely to be wrong here, because it depends on the insulation of your specific tank. The 1.5 kWh default is a reasonable modern figure; an old uninsulated cylinder can be double that, and a tank jacket costs very little against it.
Where this tool stops
Heat pump performance falls in cold weather and the 3.0 figure is an annual average, not a winter one. Standing charges, gas meter conversion factors and any time-of-use tariff are outside this — it prices energy at one flat rate per kWh.
Explained in our guides
All guidesFrequently asked questions
Is a tankless water heater cheaper to run?
It has no standing loss, which is its whole advantage — heating the water you actually use costs about the same either way. So the saving equals whatever your tank loses doing nothing, typically 1–2 kWh a day for a modern tank and 2–3 for an old one. Work out that figure first: on a well-insulated tank it is often too small to justify the change on running cost alone.
How low can I set the thermostat?
Not below 60°C on a storage tank. Legionella multiplies between about 20 and 45°C and a tank of stored water at 50°C is a hospitable place for it. An instant heater stores nothing, so a lower setting there is safe and does save money. If scalding is the concern on a tank, the correct fix is a thermostatic mixing valve at the outlet, not a lower thermostat.
Is there a limit on how often I can use the Water Heater Cost Calculator?
It is free, with no account, no trial and no daily cap. Every calculators tool on inputtesthub.com works the same way: open the page and use it.
Does anything I enter leave my computer?
No. The Water Heater Cost Calculator runs entirely in your browser using JavaScript. Because the work happens locally, the page also keeps working if your connection drops, and closing the tab is all it takes to discard everything.
What is the equation behind the Water Heater Cost Calculator?
It uses useful heat = litres × 4.186 × temperature rise ÷ 3,600 kWh. Divide by the heater efficiency for what it draws, then add the standing loss, which scales with tank size and with how far above the room the water is held. The full working is printed under the result, so you can follow every step rather than trusting a black box.
What is the Water Heater Cost Calculator used for?
The most common reasons people reach for it: deciding whether a tankless heater would pay for itself. Seeing what the thermostat setting actually costs. Comparing gas against electric against a heat pump on your own prices. It is built for exactly those cases rather than being a general-purpose tool with this bolted on.
Is there anything the Water Heater Cost Calculator cannot do?
Heat pump performance falls in cold weather and the 3.0 figure is an annual average, not a winter one. Standing charges, gas meter conversion factors and any time-of-use tariff are outside this — it prices energy at one flat rate per kWh. Knowing where a tool stops being trustworthy matters more than the cases where it works.
What figures does the Water Heater Cost Calculator work from?
Electric resistance is ≈ 98% efficient. Gas storage is ≈ 70%. Heat pump is ≈ 300% — it moves heat, not makes it. These are printed on the page itself, so you do not have to take them on trust.
Is the number rounded?
The calculation runs in double precision and the result is shown to ten significant figures, so converting a value and converting it back returns the original. What is displayed is rounded for readability; what is copied is not.
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