Diesel exhaust smell with Webasto heater

[ihe2]

We take both combustion and heating air from the outside, and I have not noticed any odour nuisance. I slightly disagree with mr "goboatingnow". The air heating the cabin should also be taken from outside, because then the humidity content of the cabin air will be lower compared to circulating the same cabin air. The latter is ofcourse more energyefficient.

We have the same heater (new) Webasto 5500 which is very well sufficient for our largeish boat in the Finnish climate during the usual not so warm sailing season, even though we keep its 5 large doradevents always open. As a result we’ve always had a very dry and odourless boat.

In winter if it is below -5 degrees Celsius I close the dorades and the boat warms up inside to a comfortable working temperature in a few hours if helped with an electric heater at first.

[goboatingnow]

Originally Posted by ihe2

We take both combustion and heating air from the outside, and I have not noticed any odour nuisance. I slightly disagree with mr "goboatingnow". The air heating the cabin should also be taken from outside, because then the humidity content of the cabin air will be lower compared to circulating the same cabin air. The latter is ofcourse more energyefficient.

We have the same heater (new) Webasto 5500 which is very well sufficient for our largeish boat in the Finnish climate during the usual not so warm sailing season, even though we keep its 5 large doradevents always open. As a result we’ve always had a very dry and odourless boat.

In winter if it is below -5 degrees Celsius I close the dorades and the boat warms up inside to a comfortable working temperature in a few hours if helped with an electric heater at first.

It’s a “call “ in all 4 Installs I’ve done cabin air is drawn in from inside. The outside air has too much moisture in it and drawing that in and warming it makes things worse and increases condensation as well as being energy inefficient as the cold air must be repeatedly heated.

[ihe2]

Your claim that the air outside is always more humid is not true. This is just basic physics, there are two different ways of expressing humidity:

The absolute humidity of air: in units of g/m3 or g/kg (how many grams of water are in a cubic or kilogram of air).

Relative humidity: often RH (relative humidity, the moisture content of the air at the temperature of interest as a percentage of the maximum humidity of the air).
For example, at 5°C the maximum humidity in air is about 4.8 g/m3 and at 20°C about 17.3 g/m3.

So the colder the air, the less moisture it can hold.

To be meaningful, the discussion must be based on facts.

[pcmm]

Originally Posted by ihe2

Your claim that the air outside is always more humid is not true. This is just basic physics, there are two different ways of expressing humidity:

The absolute humidity of air: in units of g/m3 or g/kg (how many grams of water are in a cubic or kilogram of air).

Relative humidity: often RH (relative humidity, the moisture content of the air at the temperature of interest as a percentage of the maximum humidity of the air).
For example, at 5°C the maximum humidity in air is about 4.8 g/m3 and at 20°C about 17.3 g/m3.

So the colder the air, the less moisture it can hold.

To be meaningful, the discussion must be based on facts.

This is correct, however heated dry air "feels" colder, its why in homes we ADD moisture to heated air to "condition" it. Recirculating the boats "inside" air will allow it to pick up moisture from the interior and make the boat feel more comfortable. For comparison, in homes we don't bring in outside air to heat it for the interior, you recirculate the inside air. Its more efficient and more comfortable. Combustion air however ALWAYS comes from outside much safer that way.

[ihe2]

Ok, I didn't think about the importance of the heating culture. In Finland, even in the coldest temperatures, you don't artificially increase the relative humidity of the indoor air in your home. If you are cold, just turn up the heating. A typical temperature in a Nordic apartment is about 22 degrees which seems to be appropriate.

But back to the topic itself, if you take 5°C air from outside and heat it to 20°C, each cubic metre of heated air can absorb 12.5 g of moisture from the interior before it reaches its maximum concentration. If for some reason more moisture is constantly being generated (wet rainwear, boiling water, ...) this excess moisture will start to condense on the cooler surfaces of the boat. When warm air meets a cold surface, the ability of the air to absorb moisture is reduced, causing the moisture trapped in the air to accumulate on the cold surface. This will eventually happen in both options, but it will happen earlier when heating circulates the interior air of the boat.

So, for example, wet rainwear will dry faster when using heated outdoor air than when using recirculated indoor air. The humidity problem is exacerbated as the interior volume of the boat is reduced, as there is less air to absorb moisture.

We obviously have different needs and preferences on this issue as well, so let's each do what we think is best! Personally, I prefer a dry and odourless boat.

[goboatingnow]

Originally Posted by ihe2

Ok, I didn't think about the importance of the heating culture. In Finland, even in the coldest temperatures, you don't artificially increase the relative humidity of the indoor air in your home. If you are cold, just turn up the heating. A typical temperature in a Nordic apartment is about 22 degrees which seems to be appropriate.

But back to the topic itself, if you take 5°C air from outside and heat it to 20°C, each cubic metre of heated air can absorb 12.5 g of moisture from the interior before it reaches its maximum concentration. If for some reason more moisture is constantly being generated (wet rainwear, boiling water, ...) this excess moisture will start to condense on the cooler surfaces of the boat. When warm air meets a cold surface, the ability of the air to absorb moisture is reduced, causing the moisture trapped in the air to accumulate on the cold surface. This will eventually happen in both options, but it will happen earlier when heating circulates the interior air of the boat.

So, for example, wet rainwear will dry faster when using heated outdoor air than when using recirculated indoor air. The humidity problem is exacerbated as the interior volume of the boat is reduced, as there is less air to absorb moisture.

We obviously have different needs and preferences on this issue as well, so let's each do what we think is best! Personally, I prefer a dry and odourless boat.

In my experience diesel heaters will struggle where outside air falls below 5 degrees. They struggle to elevate the air temperature. Tbd air coming in over the water tends to be Extremely damp to boot. Hence my preference is to reheat the internal air and in 4 self installed I’ve been happy with the result.