Flues, exhaust systems for gas appliances, naturally discharge the flue gases out of the house.
We can distinguish a number of exhaust systems for gas appliances:
1. Exhaust systems for the traditional gas fires;
2. Exhaust systems for closed gas fires;
3. Exhaust systems for open gas fireplaces (open combustion);
4. Renovation of existing flues by means of flexible or rigid pipes.
1. Exhaust systems for traditional gas fires
The traditional gas fires take the combustion air from the living area. The flue gas discharge happens through natural draft.
There are a number of specific aspects:
- Flue diameter is equal to connection size on the appliance, usually a diameter around 100 mm;
- Flue outlet at the roof; to guarantee proper operation of natural draft, the proper way of installation must be determined in advance. The outlet must be in the vicinity of the ridge, in the case of a gable roof. Any adjacent building (e.g. expansion) may adversely affect the natural draft of a exhaust system. In some cases a special chimney cap can be applied (so- called Giveg cap). This cap protects the flue against wind and prevents back draft.
- The flue should be installed as vertical as possible. Application of right-angled bends and horizontal installations should be limited.
Types of material
Van Manen fires and stoves only works with stainless steel flues. The temperature of the flue gases is approximately 250 °C. The various systems are equipped with a NEN or CE label.
Ensure a fireproof installation. All systems must be equipped with a fireproof casing or finish.
2. Exhaust systems for closed gas fires
The closed gas fires are equipped with a so-called concentric duct system. This duct system is made up of an inner duct for the flue gas discharge and an outer duct around it so the air supply can occur between both ducts. The system operates on natural draft.
A number of specific aspects are:
Gas appliance and concentric exhaust system constitute 1 installation, i.e. the correct operation of the gas appliance is inextricably linked to the correct choice of the duct system and its installation. Each manufacturer prescribes the correct type of flue and supplies self- approved exhaust material;
Flexible installation possible; there are appliances that can directly debouch at the façade, and usually it can also happen via the roof. Unlike traditional exhaust systems, it is not necessary to debouch near the highest point of the house;
Material and diameter: thick-walled aluminum, galvanized steel or stainless steel in various diameters. The material must be CE certified. Van Manen fires and stoves only works with stainless steel flues.
Ensure a fireproof installation. All systems must be equipped with a fireproof casing or finish, so the surrounding structure is protected against fire.
3. Exhaust systems for open gas fireplaces
In gas fireplaces, the duct diameter is on average larger than with other gas appliances. The dimensions of the fireplace, in combination with the applied chimney height determines the flue diameter. Existing open fires which were previously used to burn wood in, are generally suitable for gas burning.
Focus areas are:
Gas temperature is quite low, around 150°C;
Construction materials: Van Manen fires and stoves only works with stainless steel flues;
Independent systems are double-walled, made of stainless steel with insulation between the inner and outer ducts. These exhaust systems are also suitable for wood burning. An alternative is a double-walled stainless steel duct with an air gap between the inner and outer ducts;
Flue outlet and installation: this is an exhaust system that operates on natural draft. The outlet area must therefore be neutral (pressure; see Exhaust systems for the traditional gas fires). The flue will have to be installed as vertical as possible, use up to 2 turns of 45 degrees if you have to divert.
Ensure a fireproof installation. All systems must be equipped with a fireproof casing or finish. With gas fireplaces, various safety measures must be taken into account, see the ‘Chimney fans’ brochure.
For the outlet at the roof, the smoke nuisance for the environment must be taken into account. In the NEN 2757 norm are requirements drafted. The installation instruction from the supplier provides directions as well. Environmental nuisance is also applicable for all flue outlets of both gas and wood appliances.
Renovation of existing flues
Renovation of existing flues by means of a flexible or rigid pipe If a gas appliance is connected to an existing masonry flue, it is usually necessary to renovate this flue. Older flues can be torn. As a result, flue gases leak into the living area. Flue gases released by gas combustion are colorless and almost odorless. This poses a danger to the people present. The flue gases also contain water vapor. This water vapor will condense on the relatively cold stone inner wall of the flue. This condense can cause problems. If a traditional gas fireplace is connected to an existing flue with a relatively large diameter, renovation can also be advised. The flue gases cool significantly on the larger inner surface area, resulting in a poor draft.
For closed gas fires there is also a possibility for renovation.
If the existing flue has a sufficient diameter (Ø 150mm), an inner duct (Ø 100mm) can be installed. The air supply will take place between this inner duct and the existing duct. The flue gases are discharged through the new inner duct. Both rigid and flexible pipes can be used for this.