Heating from a 33 kg cylinder - Combination boiler consumes 33 kg of gas per wee

Agata1985 113160 32

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Why is a Junkers combination boiler using a 33 kg propane cylinder in only five to seven days while heating a 33 m² apartment, and what should be checked?

The excessive consumption and three-minute cycling were caused by a faulty boiler control board: the boiler overheated, shut down on its safety mechanism, and repeatedly restarted; an authorised technician confirmed this fault. [#12026613] The reported rate of about 5 kg of propane per day is nevertheless very high, so the burner settings and conversion for LPG should also be checked by a qualified service technician. [#11838188] Significant heat loss is expected because the apartment is a high-ceilinged ground-floor corner unit in an old, uninsulated tenement; insulating the basement ceiling and external walls should be prioritised. [#11825713] The radiators may also be undersized, causing the room thermostat to demand continuous heating while the water quickly reaches the boiler’s shutdown temperature; verify that radiators heat fully and assess whether larger radiators and an appropriate heating-water temperature are required. [#11851698]

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#31 12045217 11 Mar 2013 10:46

Anonymous Anonymous

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Post #31
12045217 11 Mar 2013 10:46

lopq wrote:
And home propane heating is equal to or more expensive than electrics. From what I read earlier, this installation works at the performance limit. The proof is that the cylinder with a propane-butane mixture is freezing. (..)

New laws in chemistry and physics? What is the evidence of low performance?
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Use room regulation and economical temperature cycling
#32 12048392 11 Mar 2013 21:50

serwisszulborski.pl serwisszulborski.pl

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Use room regulation and economical temperature cycling
Post #32 12048392 11 Mar 2013 21:50

It is worth using the room regulator and playing with the program. "Dredge" the day to on-off, set economical temperatures, eg 20 * C on - 18 * C off. The boiler has short breaks between one cycle and the next, and this largely adds to the costs ... When heating with propane, it is not worth buying a boiler from the bottom shelf, where there is not much you can do. Setting the power of 8 kW or 12 kW will not change much.
#33 12060509 14 Mar 2013 19:02

rogera rogera

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12060509 14 Mar 2013 19:02

I already rolled a similar topic on another boiler. With this type of LPG fueling, the cylinders (at least 2-preferably 3) should be connected to one battery and work on a common regulator. The reason for switching off the boiler is the lowering of gas efficiency from the cylinder during use due to the drop in supply pressure. The minimum supply pressure switch (in LPG-fired boilers should be included in the boiler equipment) registers too low pressure and turns off the burner. After some time the cylinder heats up, the pressure will increase and the boiler will try to ignite again. Until the end of the world. LPG is one of the most expensive carriers. I suggest using a different type of fuel.
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Topic summary

The discussion revolves around a user experiencing high gas consumption with a Junkers Ceraklass dual-function boiler, using a 33 kg propane gas cylinder every 5-7 days to heat a 33 square meter apartment. The user notes that their boiler operates inefficiently, turning on every 10-15 minutes after installing a programmable thermostat, compared to a neighbor's similar boiler that operates every 40 minutes. Responses highlight potential causes for the excessive gas usage, including heat loss due to poor insulation, high ceilings, and inadequate radiator capacity. Suggestions include consulting a service technician for proper boiler adjustment, insulating the basement, and possibly increasing radiator size to improve heating efficiency. The user later discovers a fault in the boiler's control board, which contributed to the inefficiency.
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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].

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