Honeywell OT35

Product detailed description

Honeywell OT35 - outdoor temperature sensor for weather-compensated control.

The sensor measures the outdoor air temperature and sends it to the boiler’s control unit (designed for Attack Maximus). Based on the outdoor temperature, the control continuously adjusts the heating water temperature so that a stable temperature is maintained in the house without unnecessarily increasing the boiler’s output.

Installation

The sensor is mounted on a shaded north- or north-west-facing side of the facade, away from direct sunlight and other heat sources, and is connected to the terminal block of the boiler’s control unit.

Frequently asked questions

• How do I choose the right output for a HONEYWELL condensing boiler? The starting point is the calculated heat loss of the building being heated (most reliably from project documentation or an energy certificate). If you don’t have a project, you can estimate roughly 60-100 W per m² of floor area for a typically insulated house built after 2000, or 100-150 W/m² for an older, uninsulated house - the exact figure varies depending on the number of floors, ceiling height, number and quality of windows, and building orientation. A boiler oversized for the required output switches on and off more often (so-called cycling), which shortens its lifespan and reduces efficiency; an undersized boiler, on the other hand, cannot adequately heat the house on freezing days.
• Why is a condensing boiler more economical than a conventional one? A condensing boiler additionally makes use of the heat hidden in the water vapour produced when gas is burned - in a conventional boiler this vapour escapes unused through the flue, while in a condensing boiler it is cooled below the so-called dew point, the vapour condenses, and the released heat is returned to the heating circuit. As a result, condensing boilers achieve an efficiency of roughly 105-110% relative to the calorific value of the gas, compared with the usual 85-92% for conventional boilers.
• What type of flue gas discharge does this boiler need? Most modern condensing boilers are so-called “turbo” boilers (with a sealed combustion chamber) and require a coaxial (concentric) or twin-pipe flue gas discharge and combustion air supply routed through an external wall or the roof - so a functioning chimney is not needed. You will find the exact type and maximum length of the flue (depending on the 60/100 or 80/125 mm diameter) in the technical documentation for the specific model, or you can consult our customer service.
• What does the ErP energy class shown for the boiler mean? This is a mandatory efficiency label for heating appliances under the EU ErP (Ecodesign) directive, similar to the energy labels used for refrigerators. Condensing boilers typically achieve class A, or higher in combination with room controls (e.g. A+ when using weather-compensated control and a room thermostat).
• Can I install and connect this boiler myself? No. Connection to the natural gas supply, the electrical network and the flue gas discharge must by law be carried out exclusively by a person with the relevant authorisation (usually an authorised service technician for the given brand or a certified gas appliance technician). After installation, the boiler must be commissioned by the manufacturer’s authorised service - this is also usually a condition for the warranty to be valid.
• What about servicing and the warranty? Most manufacturers require a regular annual service inspection by an authorised service provider in order for the warranty to remain valid even after its standard expiry (an extended warranty subject to regular servicing is common especially for the Vaillant, Protherm and Viessmann brands). You will find the exact warranty conditions in the warranty card supplied with the boiler.
• What is included in the delivery of this specific product? The exact package contents (the boiler itself, possibly a hot water tank, room controls and other accessories in the case of a set) are stated in the product name and in its technical parameters above on this page.