Troubleshooting and Repairing Common Ventilation Issues

We have already published several articles on factors that must be taken into account when designing and installing a mechanical ventilation with heat recovery system (MVHR), as well as common practices that should be observed in order to maintain your installation and ensure that it runs efficiently for several years to come.

The majority of issues that owners of a mechanical ventilation system are likely to experience can unfortunately be traced back to installer error, or inadequate cleaning and maintenance by the building occupant. Common problems with MVHR systems include:

• Poor initial MVHR design – If your installation has not been optimised to the size of the property, you are likely to experience efficiency problems. Too large, and your system will exceed the requirements of the building while consuming excessive energy. You will therefore fail to generate the savings on heating costs that you may have been hoping for. Too small, and the unit will be overworked, meaning you are likely to experience signs of wear sooner than would otherwise be the case.
• Cheap ducting or a cheap MVHR unit – The old adage that "you get what you pay for" certainly rings true when it comes to mechanical ventilation. Cheap ducting is more susceptible to leaks and tears, while a cheap unit will wear out quickly or fail to perform as required. Cheaper units can also tend to be excessively noisy.
• Installer error – This refers to instances where the system has been designed properly, but the installers have changed duct routing, have not sealed the ducts properly (thus allowing air to escape), or have accidentally or negligently crushed a section of ductwork, resulting in the escape of recirculated air before it can get to the rooms.
• Inadequate commissioning – The proper measurements and balancing measures to ensure suitable airflow to each room have not been carried out.
• Dirty or clogged filters – Responsibility here lies with the building occupant. Regular inspection and cleaning are required, alongside good general hygiene practices to avoid the build-up of dirt and dust in the home.

We will now provide a brief guide on troubleshooting ventilation issues, identifying some of the symptoms caused by the issues outlined above, and providing some tips on how to rectify problems and repair your ventilation system, with a view to ensuring the continuous and efficient operation of your installation. This should hopefully achieve the desired return on investment in terms of cost savings and user benefit (improved air quality, contribution to environmental protection, etc.).

1. My installation is excessively noisy

Noise can be experienced if ductwork is undersized or has been poorly installed. Other potential causes of noise include blocked or dirty grilles and vents. If your central unit is undersized, motors will have to work at a higher speed, resulting in increased noise. If ductwork is too narrow or if the size of the duct ends does not match the corresponding connection, this can result in fluctuations in airflow pressure, which can generate unwanted noise.

Solutions to the above noise issues include the installation of noise attenuating vents. If sections of rigid ductwork are causing connecting fixtures to vibrate, these can be replaced with flexible ducting, although be careful not to overdo it, as flexible ducting is more fragile and susceptible to leaks and breakage. You should also ensure that your central ventilation unit is mounted on a fixed and secure base. For further information on ventilation noise and appropriate solutions, read our article on acoustic ventilation.

2. My system is not running efficiently

If you still feel the need to continually run your central heating, or if powering your system is causing sky-high electricity bills, there are various possible reasons as to why your system may be running inefficiently. Again, many of these can be traced back to poor system design or installation error. Some MVHR systems are intended for installation in properties such as flats or apartments, others for large houses, or even some commercial/industrial options. Check that these are fit for purpose using the product label and datasheet that should have been left following installation.

You should also ensure that your central unit is installed in an insulated space where possible. While an MVHR unit may feature an insulated casing, most manufacturers stipulate that they should not be installed in uninhabited, uninsulated rooms.

3. I have discovered leaking water

You may encounter water leaking from MVHR units and air valves/grilles, which collects in the loft ducts. This may be because the condensate drain attached to the MVHR unit hasn’t been installed properly. If water coming through valves/grilles is collecting in your ducts, it’s almost certainly because the person who fitted your system hasn’t used the recommended insulated ductwork.

4. Air from vents is cold rather than hot

This problem can again be the result of your central ventilation unit being installed in an uninsulated space. If ducting is poorly designed, without insulation, and running over long distances in cold parts of the building, the heated air may cool before it reaches its target rooms. While not a great deal can be done about poor routing design, insulation can of course be retrofitted to ducting, or ducting can be replaced with a more suitable product.

5. I am still experiencing poor indoor air quality

Whether you have recorded unsatisfactory levels of certain pollutants using sensors,, or have simply observed a deterioration in indoor air quality, fluctuating indoor temperatures could be a sign that your ventilation unit is not properly regulating heat transfer. Increased humidity may be a result of poor airflow. While this may indicate a more serious problem with your central unit or fans, it may be that vents are dirty or clogged, and a thorough clean or the replacement of your filters may improve the issue.

Many of the problems discussed above may be resolvable with regular cleaning and the replacement of wear parts, which can be performed without the need for professional assistance. However, problems involving more thorough testing and structural work will require that you consult an expert. If you are experiencing issues with your MVHR system, or want to arrange a service, contact EnviroVent and we can provide any necessary advice and put you in touch with an approved technician in your local area.

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