FAQ
TL;DR: 1000 L of water absorbs a 25 kW batch without boiling; "A fully filled 25 kW boiler will never boil 1 000 L" [Elektroda, andrzej lukaszewicz, #18097876]. Size pipes ≥5/4" and add a thermostatic mixing valve for 40-70 °C control. Why it matters: Correct hydraulics prevent overheat, air entry and costly rework.
Quick Facts
• Boiler-to-buffer pipe: ≥5/4" (DN32) or 6/4" (DN40) to keep natural circulation efficient [Elektroda, andrzej lukaszewicz, #18078885].
• Adjustable return temperature: 40-70 °C using ZT or TS 1" valve + capillary sensor [Elektroda, andrzej lukaszewicz, #18082433].
• DIY Laddomat substitute parts ≈ 800 PLN (pump, TS valve, fittings) [Elektroda, andrzej lukaszewicz, #18082433].
• Expansion riser: first vertical ≥0.1 m; total horizontal ≤10× that length [Elektroda, hajtaler, post #18085039]
• Heat capacity: 1 kL water × 1 °C ≈ 1.16 kWh [Engineering Toolbox].
How large should the buffer be for a 60 kW chip-fuel boiler?
Target at least 2 000 L. A 60 kW unit can raise 1 000 L by 50 °C in ≈0.8 h (60 kW ÷ (1.16 kWh · 50 °C)=0.86 h) [Engineering Toolbox]. Doubling the volume stretches burn time and lowers cycling losses.
Why do experts insist on ≥5/4" pipes between boiler and buffer?
Large pipes cut resistance and let water move under gravity during power loss. Andrzej notes 5/4–6/4" “facilitates work in natural circulation” [Elektroda, andrzej lukaszewicz, #18078885]. Smaller pipes risk boiling and pump cavitation.
Do I really need valves between the boiler and the buffer?
Yes. Gate or ball valves let you isolate the 1 000 L tank for service without draining it [Elektroda, hajtaler, post #18086446] Place them low, on both flow and return, to retain natural circulation when open.
Is a check valve required on the return to the buffer?
Install one. It stops the three-way DHW mixing valve from pulling cold water straight out of the buffer rather than the radiator return [Elektroda, hajtaler, post #18097051]
Can the system run safely during a blackout?
With open-vented buffer, big pipes and a flap (swing) valve, heat can move by gravity. "A fully filled 25 kW boiler will never boil 1 000 L" in such layout [Elektroda, andrzej lukaszewicz, #18097876]. Keep the riser unobstructed and pumps off.
What is the downside of putting an automatic air vent above the buffer?
On the pump’s suction side negative pressure forms and the vent can draw air, not expel it [Elektroda, hajtaler, post #18084596] Move the vent to the boiler top or close it after purging.
Why does the seller recommend a four-way valve for the carpentry shop?
Four-way (or three-way plus pump) blends supply and return. It keeps the boiler return above 55 °C, preventing tar and extending exchanger life on chip fuel [CIBSE Guide B].
How do I connect the open expansion vessel correctly?
- Run a continuously rising safety riser (RB) straight from boiler top.
- Maintain first vertical ≥10 cm before any bend.
- Limit total horizontal length to ≤10× that vertical [Elektroda, hajtaler, post #18085039]
Is a 1-function BVTS cooling valve necessary in an open system?
Not mandatory, but allowed. Open vent plus gravity return already protect the boiler; BVTS adds redundancy and opens at 95 °C [Elektroda, hajtaler, post #18086446]
What pipe sizes for radiators and air heaters?
Typical: DN25 (1") supply loop for two 25 kW heaters up to 20 m, DN20 (3/4") branches to aluminium radiators. Verify by flow rate: 0.86 m³/h needs ≤0.4 m/s for low noise [Viessmann Design Data].
How can I build a budget alternative to Laddomat?
Combine a high-Kv 1" TS mixing valve, any Class A pump, flap valve, filters and shut-offs. Andrzej priced the set at ≈800 PLN, about half a branded unit [Elektroda, andrzej lukaszewicz, #18082433].
Quick 3-step method to size a buffer tank?
- Pick desired burn time (h). 2. Multiply boiler kW by hours, then divide by 1.16 to get litres per 10 °C. 3. Multiply by planned ΔT. Example: 60 kW ×1 h ÷1.16 ×50 °C ≈2 600 L.
What is a common failure when DIY owners ignore slope rules?
A horizontal safety riser longer than allowed can trap steam, leading to water hammer and vessel overflow during overheat events [Elektroda, seiko.36, post #18083914]
