Passive House

Passive House – A Sustainable Investment

A passive house provides consistent, comfortable temperatures in winter as well as summer without using conventional heating or air conditioning systems. Using the existing temperature provided via solar radiation through the windows as well as the heat from appliances and inhabitants is sufficient.

The required heating energy for a passive house is only 10% of that needed for a conventional house. These extraordinary savings are rooted in the two basic principles of minimising thermal loss and optimising thermal gain.

Importance of windows

The window in a passive house plays a prominent role in two ways – firstly, the heat loss despite large glass surfaces can be reduced and secondly, windows increase the possibility for heat gain through solar energy. Internorm‘s highly thermally insulated windows do this exceptionally well: thermal insulation glazing as used in passive houses achieves Ug values of up to 0.4 W/m2K.

Essential principles for the construction of passive house windows:

  • Highly thermally insulated glazing

  • Highly thermally insulated frame

  • Thermally optimised edge seal

  • Expert installation, thermally optimised

The Criteria for Passive Homes


One of the major criteria of a Passive Home is the active utilisation of existing energy – minimising thermal losses at the same time optimising thermal gain, these are the basic principles. But merely combining passive house certified components is not enough to reach a passive house construction standard: The whole project is more than the sum of its parts – mutual interactions between the distinct components necessitate integral planning to fulfil three basic criteria:

  • Heating  < 15 kWh/m²a

  • Primary energy (heating, warm water, house appliances) < 120 kWh/(m2a)

  • Pressure difference air exchange n50 < 0.6 h-1, i.e. at a pressure difference of 50 Pascal the air flow must be less than 60% the building’s volume per hour.

PASSIVE HOUSE windows: Dual capacity
tonnes CO2 / year
Heating cost demand and CO2 emissions per year
tonnes CO2 / year
old building low energy house
passive house kWh/m2a kWh / m2a


The passive home needs a tight highly thermally insulated outside shell and a controlled house ventilation with mechanical heat recovery. This plays a key role with passive houses. It ensures hygienic air and takes away humidity and odours from where they arise. If you were to achieve this with airing via the windows, the resulting heat losses would be greater than the overall heating demand. Therefore, controlled house ventilation is indispensable for passive houses. It reduces ventilation heat loss considerably as the energy of the used air is utilized to pre-warm the fresh air. This energy would be irreversibly lost with conventional airing. Air enters the house via occupied rooms and will be extracted from the kitchen, bathroom and toilet areas so that unpleasant odours do not spread around the house.

Passive House Cert WINDOWS & DOORS

Internorm is the number 1 in passive house windows and the only window manufacturer in Europe with nine passive house certified components. That means that nine window and door systems have been certified by the “Passivhausinstitut Dr. Wolfgang Feist”.

The UPVC or UPVC/aluminium window KF 410 as well as the timber/aluminium window HF 310 are two of these windows in their standard version shown to be best suited for passive houses. They were tested and passive house certified at the independent institute in Rosenheim as well as at the TU Graz.



As the energy demands of a passive house are reduced by up to 90% heating costs and therefore CO2 emissions can be reduced drastically – compared to a conventionally constructed building, on average 4,000 kg of greenhouse relevant carbon monoxide are avoided each year.

This would correspond to driving about 27,000 km with a typical 6 litre car. Therefore, constructing energy efficient passive houses supports climate protection sustainably and saves on limited resources such as oil or gas.