MVHR ducting 125 mm to 150mm

[SLABdan]

Hi all, just unboxed my order from BPC to see wrong duct size specified for my MVHR unit. I have limited time to get it in and so need a solution which doesn’t involve either sending everything back or buying a new MVHR unit.

 

125mm spigot on my machine, 150mm duct sent to me. Question is, can I just use a reducer immediately at the spigot. Would this cause me any issues, I presume my unit is designed for an airflow based around 125mm, but with the very short runs (sub 1m) I have to manifolds and intake/exhaust. Will I have an issue?

 

thank you! Also really looking forward to being in the loft at 31c 🤣

[JohnMo]

Just a 125 to 150 adapter at spigot. You can get them from Screwfix or Toolstation normally a stock item.

 

Is the spirit on the MVHR unit is 125mm that will be all it needs. Having bigger duct attached will reduce the flow velocity, so reducing noise and resistance. Less resistance lets fan run lower on its curve for less noise - big duct is win, win for noise.

[SLABdan]

Brilliant! You’re a top man JohnMo

[JohnMo]

21 minutes ago, SLABdan said:

loft

Loft install - insulated everything, including the manifolds and pipes either side.

 

Ensue your condensation drain is done correctly with suitable slope and a dry trap is installed.

[SLABdan]

Yep, pipes will be in 300mm of insulation. I have foil insulation for the 150mm ducts. Condensate drain goes to soil stack. What a miserable day in the loft that was!