Chimney requirements
Specify the UNI 60 flue — 8 in minimum diameter, acid-resistant 316 stainless steel, insulated where exposed, to EN 1856-1 and EN 1856-2.
The UNI 60 needs an 8 in chimney in acid-resistant 316 stainless steel, and the flue must never be narrower than the boiler's outlet. Draft is what makes a solid-fuel boiler work; an undersized or cold chimney will smoke into the room, tar up quickly and lose you efficiency.
Specification
| Requirement | Value |
|---|---|
| Minimum diameter | 8 in — never less than the boiler flue outlet |
| Material | Stainless steel 316, acid-resistant |
| Construction, inside a brick channel | Single wall |
| Construction, exposed | Double-walled (insulated) |
| Standards | EN 1856-1:2013 part 1 (metal chimney requirements) · EN 1856-2:2013 part 2 (metal liners and connecting pipes) |
| Clearance to combustibles | 12 in, or 6 in for double-wall stove exhaust pipe |
Acid resistance is not optional
Flue gas from wood produces soot and condensation, and the condensate is acidic. Ordinary steel liners deteriorate at the joints. This is the single most common cause of premature chimney failure on wood boilers.
Design rules
Keep the inside smooth
The inside of the chimney should be smooth, with no condensation or soot deposit zones, so that draft is optimal and unobstructed.
Minimise bends
The number of chimney bends should be as small as possible. Every bend costs draft and creates a place for deposits to collect.
Insulate exposed runs
An exposed, uninsulated chimney runs cold, which drops draft and dramatically increases tar and condensation. Use double-walled insulated pipe outside heated space.
Plan for cleaning
Choose a chimney system that is easy to assemble and disassemble for maintenance, and that complies with fire safety standards. You will be sweeping it regularly — see Chimney care.
Deposition rate
How fast your chimney fouls depends on the fuel and the boiler temperature.
- Wood deposits more than coal. Tar and soot build faster on wood-fired units.
- Low boiler temperatures deposit more. Running cool, especially with a cold return, condenses tar out of the flue gas. This is the reason return-temperature protection matters — see System design.
- Wet fuel deposits far more. Fuel above 20 % moisture will foul a chimney in weeks.
Checking draft
Hold a strip of paper at the ash pit with the boiler running — it should deviate towards the ash pit. That shows air is being drawn through the boiler.
Also confirm that the ventilation openings for inflow and exhaust air have not been restricted or blocked.
Chimney fan for comfort
For best comfort and minimal fume migration into the house, use a chimney fan when starting the boiler. Smoke hoods are a second option.
Closed system, expansion tank, relief valve and return-temperature protection.
Frequently asked questions
Boiler room and clearances
Required clearances for the UNI 60 — 24 in to side and back walls, 36 in at the front, 28 in overhead — plus floor, ventilation and service access requirements.
Hydronic system design
Design the UNI 60 hydronic system — closed loop, expansion tank, safety relief valve, return-temperature protection and the recommended MBtek installation scheme.