MVHR (Mechanical Ventilation and Hear Recovery) systems work are a desirable and effective way of achieving a comfortable healthy environment on a new home.

However, to get the best out of them, you need an airtight building and in particularly really airtight windows — your typical UPVC double glazing is lot less airtight than you might think!

At the heart of airtight windows is the magic “middle gasket” — the extra seal that makes a window a triple-seal window, also known as triple gasket window.

What does the third seal actually do?

A standard window has:

• Outer seal → weather protection
• Inner seal → air barrier

A triple-seal (middle gasket) adds:

• A buffer zone chamber between inside and outside
• Much better air permeability (airtightness class)
• Reduced risk of wind-driven draughts
• Improved sound insulation

Why is this important for MVHR systems?

1. It keeps the airflow controlled (the most important factor!)
   The MHVR system is a balanced one: air in = air out. Adding random air inputs unbalances the system and reduces effectiveness.
2. It protects the heat recovery efficiency
   The MHVR system warms incoming air, but air from leakages may be cold.
3. It prevents draughts (comfort issue)
   Most draughts are caused by cool air from the window causing movement of air through convection.

4. It prevents moisture and condensation problems
   The MHVR system helps control humidity — but it is undermined by leakage elsewhere.
5. It improves air quality (a big and underrated benefit)
   Air leakage bypasses the filters entirely bringing in dust, pollen and pollution

   Airtightness means clean, filtered air actually reaches you

6. It improves acoustic insulation
   One of the benefits of an MHVR system is that the windows are mostly kept shut and therefore everyday noises such as traffic, roadworks, bin lorries, chainsaws or tractors are reduced. This is even more so with triple-seal windows as the seals can be a source of acoustic leakage.
7. It allows for larger windows
   Air leakage is magnified when you have extra-large windows or sliding doors, which may be full height and many metres wide. This is where triple seals combined with triple-glazing become absolutely essential.

What do Spectrum recommend for airtight windows?

We recommend Internorm Windows every time! We believe they are the most airtight windows available in the UK and have built up a unique reputation over the last 40 years. Internorm windows not only have the best airtightness, they have the best insulation and U_w values (as low as 0.6 W/m²K and are Passivhaus certified.

Internorm windows are often the first choice for Passivhaus builds as their combination of insulation and airtightness makes it so much easier to achieve the Passivhaus standard and to pass the tests including the airtightness text needed to get the building Passivhaus certified.

Triple Glazing
Internorm windows include triple-glazing as standard and also include technical options and innovations such as integrated shading, automated external shading, premium solar glass, concealed locking etc.

Shading options are particularly important with MHVR systems as they can help prevent overheating without needing to open windows for ventilation. Triple glazing also helps keeping the building cook in hot weather.

Aluminium-Clad
Internorm windows & doors are all aluminium-clad for long life and low-maintenance, with either timber or high grade UPVC.

Made to Order in Austria
All Internorm windows and doors are bespoke made to order an Austria and are precision engineered to impressive standards. The finish, build-quality and fittings are exception and always impressive those who have not seen then before.

Who are Spectrum Architectural Glazing?

Spectrum are a leading supplier and installers of premium, high-performance windows, doors and glazing systems. We have over 20 years’ experience in working on premium bespoke builds, extensions and renovations who understand the importance of the performance of the windows and doors to achieving a comfortable home. part of the project. We also specialise in extra large and complex glazing and have a high level of expertise in such projects.

Spectrum only supply three brands which we think match the high standards we choose to work to:

• Internorm Windows & Doors (Austria)
• Kastrup Windows & Doors (Denmark)
• Solarlux Glazing Systems (Germany)
  Premium Bifolding & Sliding doors, Glass Extensions, Balcony Glazing