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Better ventilation in homes could be considered one of the biggest factors in improving the wellbeing and comfort of the occupants, at least after heating to comfortable levels year-round has been taken care of. Is a mechanical ventilation and heat recovery (MVHR) system the ideal solution?

Poor ventilation not only means that rooms can feel stuffy, but trapped moisture can lead to condensation and black mould growth, which carries health risks. These problems are quite common in poorly designed housing, where consideration hasn’t been given to air flow through spaces, extractor fans aren’t up to the job, and airtight glazing has been installed without trickle vents – especially since, in a bid to keep heating costs down (or even just because they’re out at work all day), occupants might not regularly open windows to allow fresh air in, and stale air out.

Trickle vents are a helpful solution, surely, but they do have drawbacks. They can cause draughts, and the noise-insulating properties of the glazing are undermined. Also, trickle vents are not exactly the most aesthetically pleasing detail. It also helps to specify strong extractor fans for bathrooms and kitchens (never using the recirculating kind), and make sure that any run-on times are as lengthy as possible.

MVHR systems for better ventilation in homes

All that said, there is a solution which offer many benefits: a mechanical ventilation and heat recovery system (MVHR). This whole-house system continuously extracts stale, moisture-laden air from parts of the home such as the kitchen and bathrooms, and supplies fresh, filtered air into living spaces and bedrooms, which results in a healthy air flow around the property.

Because the system is always running, there’s no need to remember to turn on an extractor fan or open the window, and because of the heat recovery element, it means that energy (and money) won’t be wasted in the same way as with ‘traditional’ ventilation practices.

MVHR: what does it cost?

There are drawbacks, of course, the biggest being installation cost, especially if retrofitting MVHR into an existing building (which can be tricky as well as expensive). As a rough guide, you can expect to pay £4,500-£5,500 for a system in a large house (250-300m2), not including installation. There are also running costs to take into account, which are greater than running intermittent fans – though this expense can be offset a little by the fact that heat is not being lost, keeping heating bills down. How the figures actually stack up will depend a lot on the design of the MVHR system and the property, but a fairly typical unit is said to cost about the same as running a low energy light bulb, which is roughly 10p a day.

Design and installation is key, as with any building services. Mechanical ventilation and heat recovery systems can be noisy if they’re not correctly put in, and of course controls are always an important consideration. Here’s a round-up of considerations when planning a mechanical ventilation and heat recovery system installation:

  • Choosing the right location for the MVHR unit is vital, to ensure the system doesn’t create too much noise. Avoid installing it on walls adjoining bedrooms or living areas, and if acoustic casings are available from the manufacturer, then it’s well worth specifying them.
  • Size the MVHR taking into account acceptable noise levels and fan power, rather than just air flow rate. You might end up specifying a larger unit, but it will be well worth it for a quieter and more efficient system.
  • Don’t forget to include a summer bypass, so that the MVHR doesn’t provide heat recovery in the hot summer months!
  • Always ask the manufacturer to prepare or check the design and layout – most will do a design for free with a design warranty included.
  • It’s critical to choose an installer who knows what they are doing, and follows the design they are given to the letter. Adding additional bends, or providing poor sealing to ductwork joints, will jeopardise the system performance.
  • In new builds, always install the MVHR ductwork first, as this is the largest and least flexible service – most other services can be routed around afterwards.
  • Flexible ductwork may be easy to install but it creates large air resistances and significantly hampers system performance. The best installations will not use any flexible ductwork, a carefully planned installation won’t need it!

If you’d like to discuss ways of achieving better ventilation in homes, whether you’re tackling a self-build project or building a large estate (or undertaking any size of development in between), then do get in touch. please call us on 01206 266755 or email mail@ajenergy.com.