Can a passive home keep a glazed wall comfortable without a radiator?
A radiator does not have to occupy the strip of wall beneath every window in a passive home. Passivhaus Trust guidance says triple-glazed windows avoid downdraught comfort issues, allowing radiators to go where convenient in a room. The Passive House Institute’s documentation of Darmstadt Kranichstein also links window U-values below 0.8 W/(m²K) with interior surfaces above about 17°C and comfort without compensating heating surfaces. The room still needs heating, sized for its heat load and design. [1] [2]
- Passivhaus Trust guidance says triple-glazed windows avoid downdraught comfort issues, so radiators can be placed where convenient in the room. [1]
- In the Darmstadt Kranichstein project, window U-values below 0.8 W/(m²K) kept interior surfaces above about 17°C, supporting comfort without compensating heating surfaces. [2]
- Kranichstein used triple low-e glazing with a centre-of-pane Ug value of 0.7 W/(m²K); in cold winter sun, the inner surface reached 35°C or more. [2]
- Radiator size should follow room-by-room heat loss and the chosen system’s flow temperature; underfloor heating can exceed a low heat load and needs careful control. [1]
Why a radiator can move away from the window
The usual radiator-under-window arrangement addresses comfort issues associated with cold glazing. Passivhaus Trust guidance says triple glazing avoids downdraught comfort issues, so the radiator does not need to sit below the window for that reason. That guidance describes a design principle; it does not establish that every large glazed wall will feel comfortable in every climate or room. [1]
What better glazing changes
Better-performing glazing can keep the inside surface warmer, reducing the need for a heating surface to compensate for a cold window. The Passive House Institute’s Kranichstein documentation says that, in Germany, window U-values below 0.8 W/(m²K) keep interior surface temperatures above about 17°C. It connects those temperatures with thermal comfort without compensating heating surfaces. This is evidence from a specific project and its stated context, not a guarantee for every glazed wall. [2]
What the Kranichstein example shows
The Passive House in Darmstadt Kranichstein was planned from 1990 and completed in 1991. The south-facing terraced homes used specially developed triple low-e glazing with a centre-of-pane Ug value of 0.7 W/(m²K). The project documentation says that when cold winter sun shines, the inner window surface reaches 35°C or more. Its PHPP calculation used the Frankfurt am Main climate. The published details support a link between high-quality glazing and warm interior surfaces, but do not establish a maximum comfortable window height or a radiator location for other homes. [2]
Where the heat goes instead
A radiator can be placed elsewhere in the room, or the home can use another planned heat-distribution system. Radiator output and system temperatures still need to suit the room: Passivhaus Trust guidance says radiator size increases as flow temperature falls, with a balance usually struck around 30 to 40°C for heat-pump systems. It recommends room-by-room heat-loss modelling for radiator design. Underfloor heating can also work, but may provide more heat than a low-load room needs and requires careful control to avoid overheating. [1]
What to ask about your own window wall
Ask the designer for the window’s whole-unit performance, including the frame, and how the room’s heating demand will be met. Ask where the emitter will sit and what room-by-room heat-loss calculation supports its size. For a tall or unusually exposed glazed wall, ask how the specific design addresses winter comfort in the local climate. Kranichstein is useful context, but its published information does not give a window-height limit or a transferable radiator layout. [1] [2]