Four kinds of ducting are compatible with a whole house Mechanical Ventilation & Heat Recovery (MVHR) system; flexible ducting, rigid metal ducting, rigid PVC ducting, and semi-rigid (bendy) ducting. Ducting can be installed in either a 'branch' configuration, where one pipe or branch services multiple rooms, or it can be a radial system where every room has it's own dedicated air pipe, all fed from one air distribution box or manifold.

Flexible ducting in a branch configuration is frowned upon by BPEC, the body that certifies our installers, as condensation can pool in the internal spirals and can potentially become a health risk. Its fine if it's insulated and used in short lengths to connect the unit to atmosphere, but is best avoided in the rest of the property.

Rigid metal ‘spiral’ ducting in a branch configuration is difficult to work with and is susceptible to heat loss, so even if the MVHR is 90% efficient, up to 50% of the warm air inside the pipe could be lost on the way to and from the heat exchanger. Large diameter spiral ducting is typically reserved for commercial air handling systems which don't generally recover heat.

Rigid PVC ducting is certainly the most common domestic system, however it’s difficult if not impossible to clean and requires substantial boxing-in making it tricky to retrofit. A ‘branch’ ducting system with flexi, metal or PVC pipe is also prone to acoustic issues, either a whistling from the supply/extract valves nearest to the fan motors or 'cross talk' travelling from one room to another. The last thing you need is TV noise in your bedroom from somewhere else in the house.

By far the best kind of ducting in a domesitic or small commercial property is the new semi-rigid ‘radial’ ducting. The benefits radial ducting include:

• Flexible enough to thread through joists, between stud walls and other tight spaces (it's ideal for retrofit).
• Eliminates the risk of cross talk between rooms as every room has its own dedicated air pipe connected to a sound-proof manifold. The manifold also eliminates any motor noise from the MVHR fans.
• Can be cleaned in the future as it has a smooth internal bore and there are no sharp bends. While advisable at the moment, this feature is likely to become a requirement under building regulations.
• Incredibly low air resistance meaning the MVHR fans have less work to do, making the unit quieter, more energy efficient and (in theory) extending the life of the motors.
• Far easier and quicker to install as it clips together with no gluing & taping. One continuous length runs from the manifold near the unit to each room. The pipe can be cut neatly with a blunt knife rather than awkwardly with a saw. The install time is normally a lot less than that of rigid PVC ducting. It’s ideal for DIYers or builders new to MVHR work. The risk of boxing in a leaky pipe is almost nil.
• Partially insulated to reduce heat loss through the ducting. It can also be lagged with mineral wool without the condensation risks associated with PVC ducting.
• Extremely durable with a higher tensile strength than any other ducting
  

If Solarcrest design and supply your MVHR we provide everything required to install the complete system, including coils of 75mm radial ducting, 150/180mm insulated flexi ducting, exterior wall or roof terminals with flashings, adjustable supply & extract in-room air valves, appropriate switches and/or remote controllers and a dry none-return valve for the condensate drain. The only additional items required are 0.5mm twin core cable/flex if a manual boost switch is required, 22mm push fit overflow pipe, and either tie band, clips or zip ties to secure the ducting in place. These are provided if we also install your system.

For accurate supply and/or install budget costs and a list suitable MVHR units please complete our enquiry form.

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“Commissioning an MVHR at the end of the second fix used to be a nail biting process with PVC branch ducting. If there's even a tiny leak in any one of the dozens of pipe joints you'll struggle to hit the air flow rates required by building control. While repairing the leak might be easy, finding the leak above your new plastered ceiling can be a nightmare. Fortunately with the new radial ducting there are no joints in the pipe, so the risk of hidden leaks is practically nil. From an installers perspective radial ducting is definately the way forward."

Rick Marlow, Retrofit manager