I thought it high time someone clarified how free standing pellet stoves (Salamanders) should be installed correctly and why. The manufacturers installation manuals describe how it is to be done but not the reasons why! This is a big failing and is possibly why many installers don't do it correctly.
Most pellet stoves for domestic use fall into the 6 to 12 KW range and typically have an 80 mm exhaust and a 50 mm air intake. The different manufacturer's installation manuals dictate that the exhaust and air intake are "both" led to the exterior of the building. This is for obvious safety and efficient operation. Many installers in Portugal ignore this and leave the air intake to draw air from the room. There are serious problems with this as I will discuss below, why they don't follow the manufacturers clear instructions is completely unfathomable.
For convenience stoves are often mounted next to an exterior wall because in this location installers only have one wall to make holes through. If the stove is to be located next to an internal wall (where in some cases it may heat the house more efficiently), it is more complicated as there will be several walls or ceilings in which to make holes. Regardless of where it is located the installer has to make holes so it is unfathomable that they can't make an additional 50 mm hole for the air intake next to the exhaust hole at the same time.
The exhaust flue is an expensive item, stainless steel, double skinned, with a clean-out T, several neoprene seals and a cowl. The air intake is simply a short 50 mm extension and a plastic grill to prevent ingress of insects. The installer can make a reasonable mark up on the exhaust but nothing on the air intake maybe this is another reason why they can't be bothered.
The manufacturers in their "Ficha Technica" (Specifications) give all the efficiency data including heat levels, sound levels and pellet consumption. This is of course is based upon the correct installation. It is absurd to expect these figures if the stove is installed incorrectly.
Reasons to install the air intake to the exterior, in no specific order.
1. So that the stove warranty is valid.
2. That heat generated by the stove in the room is not continually wasted by being drawn in and consumed by combustion and sent out of the exhaust.
3. Cold air drawn from outside is more dense than hot air drawn from inside the room therefore combustion is more efficient.
4. Cold air drawn from outside has more Oxygen and less Carbon Dioxide than air drawn from inside the room where the opposite conditions exist due to humans or animals breathing, combustion from exterior air will be more efficient.
5. Air being drawn into the stove for inside will cause a partial vacuum in the property. This partial vacuum will reduce the efficiency of the stove when compared to the atmospheric air pressure available outside.
6. The vacuum created in 5 above will be replaced by cold, if not freezing air, being drawn into the property through any available orifice. This could be under doors and around windows or even down chimneys of unused open fireplaces in older properties creating cold drafts. In modern well sealed properties air will be drawn in through bathroom vents, kitchen extractors even gas boiler exhausts. Again freezing air will dilute the warm air the stove is generating.
7. As in 6 above gas boiler exhaust being drawn back into the property could be dangerous and lead to injury or death through carbon monoxide poisoning.
8. Without an exterior air intake air, the kitchen stove extractor efficiency will be severely reduced thus steam and cooking smells will not be extracted efficiently.
9. If the intake pipe is not led to the exterior the stove may be noisier.
10. Inefficient operation will result in increased maintenance costs and stove life.
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