multi-fuel stove fumes query

groober

Scenario:
- New Stovax 6KW Multi-fuel stove installed in house extension. The extension is a high single storey addition (1.5 storey), to a two-storey house.
- The stove does not have an external air intake spigot.
- The extension is very well insulated but certainly not airtight.
- The flue exits the external wall behind the stove via a 45 degree elbow off an internal 600 mm enamel pipe. It is twin-walled insulated pipe from there out. It extends approx 3.5 metres once outside. This includes one further 45 degree elbow to go around the eaves. At the cowl the flue is 1.5 meters above the highest part of the roof ridge.
- No extra vents have been added to the room since the stove was installed. Two of the windows in the room have air vents that have been open/closed for the problems listed below.
- The stove is in place for 10 days. Fires have been lit most days. Small to begin, then larger. The paint fumes seem to have gone at this stage.
- The room is open plan and incorporates the kitchen. This includes an extractor fan. This has usually been switched off when the stove is lit.

Problem:
- Our carbon monoxide alarm went off at 4.30 in the morning. The stove had not had fuel added since 10 p.m. that night. Both the air-wash and air-intake vents were closed. This was to let the fire die down for the night. When I went to check the alarm I could smell a smouldering wood smell on the way downstairs. No smoke was visible. On opening the stove, half a heat log(wood) had all but gone out.
This is the culmination of 10 days testing the stove. During that time there have been repeated fuel smell problems but never a sign of smoke (except a small amout when lighting and opening the door). The smell is often very strong the following morning but can also be oppressive while the stove is in use. It is worth noting however, that on the night the alarm went off, the stove had been burning fine without a smell in the room.
I am taking the curing paint smell into account here. I recognised that when it was happening and that is no longer a problem.
I started with smokeless coal and switched to dry timber but the result is the same. The CO alarm going off is obviously signifying a problem much greater that the smell of embers.
There are some trees near the flue and I cut a lot of branches back the day before the alarm incident. However, there are still trees not too far from the chimney opening. They do not extend much further up that that opening.

Question(s):
1. Why is a smell coming into the room when the stove vents are closed?
2. Is this a downdraft issue? Should I try fitting a "H cowl" or similar?
2. Does it appear likely that an air vent needs to be installed in the wall? Obviously I will install one if required but the heat loss to the room (well insulated and with underfloor heating) would be annoying if that is not the best solution. Again, if it is required, where is it best situated given the height of the room (4m at highest) and the UFH?

heinbloed

Scenario:

- The stove does not have an external air intake spigot.

and

- No extra vents have been added to the room since the stove was installed. Two of the windows in the room have air vents that have been open/closed for the problems listed below.

Well?!

You have a faulty installation and/or faulty user manual.
It is up to the operator to make sure his equipment is safe.
In the case described it seems to me (an amateur) that the fire hadn't enough oxigene for a complete combustion, it went cold. The fumes being now on low heat (excuse the amateur's expression) are further cooled by the pipe/flue ducting. And create a vacuum, they can't rise since there is nothing replacing them.
Except CO. Which can't escape because it isn't replaced by another gas (fresh air, CO2 etc.)

If you want to get something out of a flue you have let something in.
Of course this would cause a permanent draught, but better blowing money up the chimney than dying of CO2 poisoning.