Most hot water and low-temperature process heat in India still comes from a boiler burning diesel, furnace oil, gas or briquettes. For anything up to about 90 °C, a heat pump usually does the same job for a fraction of the fuel bill. This guide compares the two honestly, with a worked payback example, and shows where a boiler is still the right answer.
How the two make heat
A boiler burns fuel. At best it turns 85–90% of the fuel's energy into hot water; older or poorly maintained boilers manage 60–75%. An electric heater turns 1 kWh of electricity into slightly less than 1 kWh of heat.
A heat pump does not make heat from fuel. It moves heat that is already in the outdoor air (or in waste water, or the ground) into your water, using a compressor. For every 1 kWh of electricity it uses, it delivers about 3 to 4.5 kWh of heat. That ratio is the COP (coefficient of performance). It is highest when the outdoor air is warm and the water target is moderate, which suits most of India for most of the year.
A worked example (example rates; use your own)
A plant or hotel heats 20,000 litres a day from 30 °C to 60 °C, 330 days a year. That is about 698 kWh of useful heat a day (20,000 × 4.186 × 30 ÷ 3,600).
| Option | Assumption | Fuel per day | Cost per day | Cost per year | CO₂ per year |
|---|---|---|---|---|---|
| Diesel boiler | 85% efficient, ₹90/L | 82 L | ₹7,390 | ₹24.4 lakh | 73 t |
| Electric heater | 98% efficient, ₹9/kWh | 712 kWh | ₹6,410 | ₹21.1 lakh | 167 t |
| PNG boiler | 90% efficient, ₹55/scm | 78 scm | ₹4,260 | ₹14.1 lakh | 51 t |
| Briquette boiler | 70% efficient, ₹8/kg | 249 kg | ₹1,990 | ₹6.6 lakh | near zero* |
| Heat pump | Seasonal COP 3.5, ₹9/kWh | 199 kWh | ₹1,790 | ₹5.9 lakh | 47 t |
Fuel energy taken as 10 kWh per litre of diesel or scm of PNG and 4 kWh per kg of briquette. Grid emissions taken as 0.71 kg CO₂ per kWh. *Biomass CO₂ is usually counted as near zero, but briquette boilers emit smoke and particulates and need fuel storage and handling. All prices are examples; rates vary by state, tariff and contract.
Payback
Payback is simple: extra installed cost ÷ yearly saving. In this example the heat pump is about 70 kW of heating, running around 10 hours a day into an insulated storage tank. If it costs, say, ₹18 lakh installed (an example figure; ask for a quote for your site):
- Replacing diesel: saving about ₹18.5 lakh a year, payback about 1 year.
- Replacing electric heaters: saving about ₹15.2 lakh a year, payback about 1.2 years.
- Replacing PNG: saving about ₹8.2 lakh a year, payback about 2.2 years.
- Replacing briquettes: saving about ₹0.7 lakh a year. On fuel cost alone it does not pay back; the case rests on removing fuel handling, ash, smoke and labour.
Run your own numbers with the commercial hot water calculator or, for process duties up to 120 °C, the industrial process heat calculator.
Where a heat pump wins
- Hot water and process water from 45 °C to about 90 °C: hotels, hospitals, hostels, laundries, kitchens, dairies, food plants, plating and washing lines.
- Sites burning diesel, LPG or electricity for heat: these have the shortest paybacks.
- Sites that also need cooling: a heat pump can chill water and heat water at the same time, so both sides of the machine are useful.
- Sites with waste heat (cooling towers, compressors, effluent, chiller condensers): a water-source heat pump lifts that heat to useful temperatures at even higher COP.
Where a boiler still makes sense
- Steam above about 120 °C, or very high temperature process heat. Heat pumps for low-pressure steam exist but are specialist equipment.
- Very cheap biomass on site with labour to handle it, as the example shows.
- No spare electrical capacity, and no budget to add it.
Often the best answer is not either/or. A heat pump can preheat boiler feedwater or make-up water to 80–90 °C, so the boiler only adds the last step. The boiler stays as a standby, and most of the fuel bill goes away. See our application notes on boiler feedwater preheating and steam-generating heat pumps.
What to check before you switch
- Know your real heat demand: litres per day, temperature in and out, and when the peaks come. Fuel bills are a good cross-check.
- Size for energy, not peak: a heat pump with a well-sized storage tank runs longer at steady output; it does not need to match a boiler's burner rating.
- Check the electrical supply: the connected load and the transformer margin.
- Plan the space and airflow: air-source units need open air around them and discharge cool air.
- Keep the boiler at first as a standby or top-up until the heat pump has proven itself through a season.
Real installations
Read how heat pumps replaced or supported conventional heating at a multinational consumer-goods plant and a polymer plant, or browse 115 application notes by industry.
Want to learn more?
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