Timber kilns heated by heat pumps
How a sawmill running a 30 m³ standard kiln and a 10 m³ high-temperature kiln can heat both with heat pumps, and what it saves against a firewood-fired kiln boiler.
▶Video: Hot air from heat pump hot water
V05 · 2–2.5 minAir coils for spray dryers, stenters, kilns, paint booths and ovens
Video coming soon01Problem statement
- Long cycles, constant firing. Kilns run day and night for days at a time. Firewood boilers need constant stoking and their output drifts.
- Defects from poor control. Temperature and humidity swings cause checking, warping and case hardening, and rejected boards.
- Vent losses. Conventional kilns vent warm, moist air to remove moisture, and the heat goes with it.
- Losses between fuel and process. Burning briquettes in a boiler or heater and distributing the heat loses a quarter or more of the fuel's energy before it reaches the process.
- Compliance, safety and handling. Fired equipment brings boiler inspections, fuel storage and unloading, flue emissions and an attendant on every shift.
02Use case
The reference sawmill treats and kiln-dries rubberwood for furniture in a 30 m³ standard kiln on a 7-day cycle. A 10 m³ high-temperature kiln dries pine and eucalyptus for pallets and packaging on a 3-day cycle.
| Heat user | Process temp. | Basis | Heat, kWh/day |
|---|---|---|---|
| Standard kiln, rubberwood | Air 50–70 °C | 30 m³ × 560 kg/m³ dry × (60% → 12% MC) = 8,064 kg water ÷ 7 days × 1.0 kWh/kg | 1,152 |
| High-temperature kiln, pine and eucalyptus | Air 90–105 °C | 10 m³ × 500 kg/m³ dry × (80% → 12% MC) = 3,400 kg water ÷ 3 days × 1.1 kWh/kg | 1,247 |
| Storage and pipework standing losses | – | about 5% | 120 |
| Total useful heat | 2,519 | ||
Averaged over 20 running hours, the heat pumps need about 126 kW.
03P&ID
Tags: HP heat pump, TK tank, SG steam generator, P pump, PHE plate heat exchanger, TCV temperature control valve, TIC temperature indicating controller (panel), TT temperature transmitter, MT moisture transmitter, PT pressure transmitter, LT level transmitter, FS flow switch, NC normally closed. Process fluids are heated through their own exchanger, coil or jacket.
04Solution
System description
- A SE-UHT air-source cascade, R245fa machine of about 130 kW, air-source cascade to 120 °C, sized per project.
- A 4,000 L insulated storage tank decouples the heat pumps from the process peaks.
- The firewood or briquette-fired kiln boiler stays connected behind a normally closed valve as standby.
- Hot water at 115 °C replaces boiler water or steam in the kiln heating coils, using the existing kiln fans.
- The high-temperature kiln takes water first, and its return feeds the standard kiln coils at a lower temperature.
- The storage tank keeps kilns at temperature through the night with steady heat pump running.
Selected equipment
| Machine | SE-UHT air-source cascade, R245fa |
|---|---|
| Capacity | about 130 kW, built to duty |
| Concept | air-source cascade to 120 °C, sized per project |
| COP used | 1.7 (estimate) |
| Supply temperature | 115 °C |
| Storage | 4,000 L insulated tank |
Capacity is sized from the heat demand above. COP is an estimate until Sunniva engineering confirms the design.
Control philosophy
TT-101 at the tank top calls the heat pumps on below 110 °C and off at 115 °C. TT-102 at the bottom starts the units early when a new charge starts heating up. TIC-201 and TIC-202 follow each kiln's drying schedule, and the kiln controller sets the vents from wet-bulb temperature. The existing boiler stays as standby.
05Energy saving and ROI
Change any input to match a customer's site. Defaults are typical Indian prices for October 2026. The installed cost is a placeholder; replace it with the actual quotation.
| Existing | Heat pump | |
|---|---|---|
| Daily consumption | – | – |
| Annual energy cost | – | – |
| Cost per m³ of timber | – | – |
| CO₂ per year | – | – |
06Benefits
Fewer drying defects
Steady coil temperature lets each kiln follow its schedule closely, reducing checks and warping.
No night stoking
Kilns run on stored hot water without a fireman on duty.
Cascade use of heat
The standard kiln runs on water returning from the high-temperature kiln.
Lower energy cost
Each kWh of electricity delivers about 1.7 kWh of heat at the required temperature, against well under one kWh of useful heat per kWh of fuel burnt.
No flame on site
No burner, flue or fuel tank for this duty, and no fuel deliveries to schedule.
Solar-ready
Running hours can be placed in daylight so rooftop solar supplies much of the electricity, which also cuts CO₂ further.
07Engineering pointers
Site data to collect
- Kiln volumes, species and cycle times
- Initial and final moisture content
- Drying schedules used
- Present fuel use per charge
- Present fuel or electricity use and monthly bill
- Sanctioned electrical load and spare capacity
- Space for the heat pumps and storage, with service access
- Winter minimum ambient at site
Design notes
- Acidic kiln air. Hardwoods release acetic acid in the kiln. Use coated or stainless coils and corrosion-resistant fasteners.
- Pressurised loop. Water at 115 °C needs about 2.5 bar. Size the expansion vessel and relief valve for this temperature.
- Dehumidifying option. The standard kiln at 50–70 °C could also use a closed-loop heat pump dehumidifier dryer, which cuts vent losses further.
- Ambient correction. Ratings are at 20 °C air. Ask Sunniva for the correction at your site's winter design temperature.
- Water quality. Scale forms quickly above 60 °C. Use softened make-up and keep the heat pump loop closed, with process fluids on the far side of an exchanger or coil.
- Performance figure. The COP on this page is an engineering estimate, not a data sheet value. Sunniva engineering will confirm it for the actual source and supply temperatures.
Service and warranty
Sunniva has supplied 5,000+ heat pumps since 2012, with nine service technicians across India, including remote sites such as Leh. All components carry a one-year warranty.
Talk to us
Timber kilns heated by heat pumps
How a sawmill running a 30 m³ standard kiln and a 10 m³ high-temperature kiln can heat both with heat pumps, and what it saves against a firewood-fired kiln boiler.
▶Video: Hot air from heat pump hot water
V05 · 2–2.5 minAir coils for spray dryers, stenters, kilns, paint booths and ovens
Video coming soon01Problem statement
- Long cycles, constant firing. Kilns run day and night for days at a time. Firewood boilers need constant stoking and their output drifts.
- Defects from poor control. Temperature and humidity swings cause checking, warping and case hardening, and rejected boards.
- Vent losses. Conventional kilns vent warm, moist air to remove moisture, and the heat goes with it.
- Losses between fuel and process. Burning briquettes in a boiler or heater and distributing the heat loses a quarter or more of the fuel's energy before it reaches the process.
- Compliance, safety and handling. Fired equipment brings boiler inspections, fuel storage and unloading, flue emissions and an attendant on every shift.
02Use case
The reference sawmill treats and kiln-dries rubberwood for furniture in a 30 m³ standard kiln on a 7-day cycle. A 10 m³ high-temperature kiln dries pine and eucalyptus for pallets and packaging on a 3-day cycle.
| Heat user | Process temp. | Basis | Heat, kWh/day |
|---|---|---|---|
| Standard kiln, rubberwood | Air 50–70 °C | 30 m³ × 560 kg/m³ dry × (60% → 12% MC) = 8,064 kg water ÷ 7 days × 1.0 kWh/kg | 1,152 |
| High-temperature kiln, pine and eucalyptus | Air 90–105 °C | 10 m³ × 500 kg/m³ dry × (80% → 12% MC) = 3,400 kg water ÷ 3 days × 1.1 kWh/kg | 1,247 |
| Storage and pipework standing losses | – | about 5% | 120 |
| Total useful heat | 2,519 | ||
Averaged over 20 running hours, the heat pumps need about 126 kW.
03P&ID
Tags: HP heat pump, TK tank, SG steam generator, P pump, PHE plate heat exchanger, TCV temperature control valve, TIC temperature indicating controller (panel), TT temperature transmitter, MT moisture transmitter, PT pressure transmitter, LT level transmitter, FS flow switch, NC normally closed. Process fluids are heated through their own exchanger, coil or jacket.
04Solution
System description
- A SE-UHT air-source cascade, R245fa machine of about 130 kW, air-source cascade to 120 °C, sized per project.
- A 4,000 L insulated storage tank decouples the heat pumps from the process peaks.
- The firewood or briquette-fired kiln boiler stays connected behind a normally closed valve as standby.
- Hot water at 115 °C replaces boiler water or steam in the kiln heating coils, using the existing kiln fans.
- The high-temperature kiln takes water first, and its return feeds the standard kiln coils at a lower temperature.
- The storage tank keeps kilns at temperature through the night with steady heat pump running.
Selected equipment
| Machine | SE-UHT air-source cascade, R245fa |
|---|---|
| Capacity | about 130 kW, built to duty |
| Concept | air-source cascade to 120 °C, sized per project |
| COP used | 1.7 (estimate) |
| Supply temperature | 115 °C |
| Storage | 4,000 L insulated tank |
Capacity is sized from the heat demand above. COP is an estimate until Sunniva engineering confirms the design.
Control philosophy
TT-101 at the tank top calls the heat pumps on below 110 °C and off at 115 °C. TT-102 at the bottom starts the units early when a new charge starts heating up. TIC-201 and TIC-202 follow each kiln's drying schedule, and the kiln controller sets the vents from wet-bulb temperature. The existing boiler stays as standby.
05Energy saving and ROI
Change any input to match a customer's site. Defaults are typical Indian prices for October 2026. The installed cost is a placeholder; replace it with the actual quotation.
| Existing | Heat pump | |
|---|---|---|
| Daily consumption | – | – |
| Annual energy cost | – | – |
| Cost per m³ of timber | – | – |
| CO₂ per year | – | – |
06Benefits
Fewer drying defects
Steady coil temperature lets each kiln follow its schedule closely, reducing checks and warping.
No night stoking
Kilns run on stored hot water without a fireman on duty.
Cascade use of heat
The standard kiln runs on water returning from the high-temperature kiln.
Lower energy cost
Each kWh of electricity delivers about 1.7 kWh of heat at the required temperature, against well under one kWh of useful heat per kWh of fuel burnt.
No flame on site
No burner, flue or fuel tank for this duty, and no fuel deliveries to schedule.
Solar-ready
Running hours can be placed in daylight so rooftop solar supplies much of the electricity, which also cuts CO₂ further.
07Engineering pointers
Site data to collect
- Kiln volumes, species and cycle times
- Initial and final moisture content
- Drying schedules used
- Present fuel use per charge
- Present fuel or electricity use and monthly bill
- Sanctioned electrical load and spare capacity
- Space for the heat pumps and storage, with service access
- Winter minimum ambient at site
Design notes
- Acidic kiln air. Hardwoods release acetic acid in the kiln. Use coated or stainless coils and corrosion-resistant fasteners.
- Pressurised loop. Water at 115 °C needs about 2.5 bar. Size the expansion vessel and relief valve for this temperature.
- Dehumidifying option. The standard kiln at 50–70 °C could also use a closed-loop heat pump dehumidifier dryer, which cuts vent losses further.
- Ambient correction. Ratings are at 20 °C air. Ask Sunniva for the correction at your site's winter design temperature.
- Water quality. Scale forms quickly above 60 °C. Use softened make-up and keep the heat pump loop closed, with process fluids on the far side of an exchanger or coil.
- Performance figure. The COP on this page is an engineering estimate, not a data sheet value. Sunniva engineering will confirm it for the actual source and supply temperatures.
Service and warranty
Sunniva has supplied 5,000+ heat pumps since 2012, with nine service technicians across India, including remote sites such as Leh. All components carry a one-year warranty.