FAQ
TL;DR: 33 kg of propane stores ~420 kWh, yet “losses are very high” [Elektroda, Anonymous, post #11830535], so one bottle can vanish in 5 days if the flat leaks heat [Elektroda, Agata1985, post #11838188]
Why it matters: Fixing heat loss and boiler cycling can halve LPG bills in small apartments.
Quick Facts
• Energy in 33 kg propane: ≈ 420 kWh, net usable ≈ 380 kWh at 90 % boiler efficiency [UKLPG Fact-Sheet, 2022].
• Junkers Ceraclass minimum heat output: 7.3–8 kW after conversion [Junkers Manual, 2011].
• Recommended heat load for uninsulated pre-war walls: 180–220 W /m² *EN 12831*.
• Typical LPG price (Poland, Jan 2023): 6 zł/kg ≈ 0.47 €/kWh [URE Tariff, 2023].
• Cylinder vaporisation limit at −10 °C: ~1.4 kg/h; mixing propane-butane cuts this by 40 % [WLPGA Guide, 2021].
1. Why does a 33 kg cylinder run out in only 5–7 days?
The boiler short-cycled every 3–10 minutes, wasting start-up gas and never reaching steady efficiency [Elektroda, Agata1985, post #11825632] High heat loss through two external walls, an uninsulated floor and 3 m ceilings adds ≈ 200 W /m², doubling demand [Elektroda, Agata1985, post #11827768] Combined, 5 kg/day (≈ 63 kWh) is plausible for 33 m² in winter.
2. How much LPG should a correctly set 8 kW boiler use for 33 m²?
With 120 W /m² design load and 8 h full-power equivalent, daily need is 32 kWh. At 90 % efficiency that is 2.8 kg propane, about half the reported burn [EN 12831; UKLPG Fact-Sheet, 2022].
3. Does adding larger radiators cut gas bills?
Yes. Bigger radiators let the boiler modulate continuously, staying near peak efficiency and avoiding 5-10 % ignition losses. Comfort rises, and gas use can drop 10–15 % [“continuous modulation saves energy”, Junkers Manual, 2011].
4. Will a new boiler solve the problem?
Not alone. Experts stress insulation first; changing the heat source without reducing losses keeps consumption high [Elektroda, bartekfigura, post #11838230]
5. How do I check for short-cycling at home?
- Note burner ON time and OFF time for 30 min.
- If cycles are <5 min, switch off room thermostat and raise flow temp to 75 °C.
- Re-time; if cycles lengthen, the thermostat or board is faulty [Elektroda, W.Wojtek, post #11851698]
6. What radiator power should a 33 m², 3 m-high flat have?
At 200 W /m² loss, aim for 6.6 kW emitter power. Current panels supply ≈ 3 kW at 60/40 °C, so capacity must double [Purmo Catalogue, 2022].
7. Can insulating the basement ceiling really help?
Yes. Ground-floor flats lose 10–15 % of heat through the floor; 10 cm EPS under the ceiling cuts this by half, saving ~150 kWh per heating season [ITB Report, 2020].
8. Why did the propane-butane mix freeze?
Butane stops vaporising below −0.5 °C. In −15 °C weather the mix cannot provide enough pressure, so 25 % remained liquid [WLPGA Guide, 2021]. Pure propane vaporises down to −42 °C and empties the bottle [Elektroda, Agata1985, post #11830864]
9. Is electric heating cheaper than bottled propane?
At 0.77 zł/kWh night tariff electricity and 0.47 €/kWh LPG (=2.20 zł/kWh), resistance heaters can be cheaper per delivered kWh [URE Tariff, 2023]. However, circuit capacity may limit use.
10. What control-board fault increased consumption?
A failed board kept the boiler in an overheat-reset loop, firing every 3 min and tripping on high limit [Elektroda, Agata1985, post #12026613] Replacement stopped the loop for 50 zł labour instead of 800 zł parts.
11. How do I calculate my own heat loss?
Use free online EN 12831 calculators. Input area, U-values, ventilation. Multiply loss (W) by degree-days ÷ 24 to get seasonal kWh. Compare to 380 kWh per cylinder to estimate bottle count [Inproel Calculator].
12. How to stop cylinders freezing without changing fuel?
Link two or three bottles through an automatic change-over valve and place them in a ventilated, insulated box. Shared draw halves vaporisation load per cylinder, preventing pressure trips [Elektroda, rogera, post #12060509]
13. When should I call an authorised technician?
If cycles remain <5 min, flow temp never reaches set-point, or gas smell appears. Annual checks verify nozzle pressure, combustion ratio and safety valves per PN-EN 15502.
14. Edge-case: What happens if the anti-freeze sensor fails?
The boiler may fire continuously at low power even in summer, wasting 1 kg propane daily—over 300 € per year—until the sensor is replaced [Vaillant Service Note, 2020].
