RD4REDUC – Rytons 125mm to 100mm Reducer (125mm/100mm Dia. Range)

General Details

RD4REDUC – Rytons 125mm to 100mm Reducer (125mm/100mm Dia. Range)

  • Reduces 125mm dia. ducting to fit 100mm dia. components.
  • 100mm dia. male spigot with 125mm dia. female collar.
  • 125mm collar compatible with 125mm dia. Rigid Pipe RD51RND and suits 125mm dia. RytHose range (or use RD5HC).
  • 100mm spigot compatible with 100mm dia. Rigid Pipe RD4/RND and suits 100mm dia. RytHose range (or use RD4HCF).
  • Use with adaptor RD4FR to connect to 110mm x 54mm Flat Channel Duct RD4/M.
  • For use in areas requiring lower extraction rates such as bathrooms, kitchens and utility rooms.
  • Operating temperature range -15ºC to 60ºC.
  • Manufactured in compliance with DW 154: Specification for Plastics Ductwork.
  • Meets UL94 HB flammability standard.


  • Male spigot: 99mm Ext. Dia. x 20mm D.
  • Female collar: 125mm Int. Dia. x 20mm D.

Free Area:

  • 100mm dia. spigot: 7,283mm² (72.83cm²).
  • 125mm dia. collar: 12,266mm² (122.66cm²).

Compatible Ducting and Components:

  • Rytons Rigid Pipe 1m L RD51RND.
  • Rytons PVC 125mm Diameter RytHose Range
  • Rytons Fire Resistant RytHose 125mm Dia. FAD510M.
  • Rytons Threaded Hose Connector Female RD5HC.
  • Rytons Rigid Pipe 358mm L RD435RND.
  • Rytons Rigid Pipe 1m L RD41RND.
  • Rytons Rigid Pipe 1.5m L RD415RND.
  • Rytons Rigid Pipe 2m L RD42RND.
  • Rytons PVC 100mm Diameter RytHose Range.
  • Rytons Fire Resistant RytHose 100mm Dia. FAD410M.
  • Rytons Threaded Hose Connector Female RD4HCF.
  • Rytons Flat Channel Horizontal Adaptor RD4FR.

Airflow and Resistance:

  • 8 l/s: 0.80 Pa.
  • 13 l/s: 1.30 Pa.
  • 21 l/s: 3.20 Pa.
  • 30 l/s: 5.90 Pa.
  • 60 l/s: 24.00 Pa.
  • 120 l/s: 102.00 Pa.


  • White High Impact Polystyrene.

Reference Material:

  • The Building Regulations F1 2021, Installation of ventilation systems:
  • 1.76: Rigid ducts should be used wherever possible.
  • 1.79: Ductwork installations should be designed and installed to minimise the overall pressure losses within the system by taking all of the following steps.
    • a. Minimising the overall length of duct.
    • b. Minimising the number of bends required.
    • c. Installing appropriately sized ducts for the air flow rate.
  • Note: This approved document takes effect on 15 June 2022 for use in England.  It does not apply to work subject to a building notice, full plans application or initial notice submitted before that date, provided the work is started on site before 15 June 2023.

Handling Information:

  • Individual weight: 40g.

NBS Specification:

Rytons is proud to be a family run business and British manufacturer since 1972

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