Webasto Air Top 5500 Questions

[zboss]

Hi!

I am looking closely at adding a Webasto Air Top 5500 to the boat. I have two questions about the installation:

The installation instructions say that the combustion air intake should not draw from the cabin. Am I understanding this correctly? That there needs to be both a fresh air intake from outside and an exhaust to the outside? It seems to be straight forward but the instructions are confusing.

Also, I don't see a recommended circuit breaker size nor do I see any start up amp draw mentioned in the document. The max amps are 7.9 and based on that figure, and the distance to where I want to mount it, I'll be using 10 gauge wire. Does a 10 amp breaker sound about right?

Thanks,

- z

[cal40john]

My 3500 came with a 20 amp inline car style fuse in the power line. Webasto recommends attaching to a nonswitched power source as the heater runs the fan to cool down after stopping the fuel. Electronic damage can occur if shutdown isn't followed.

Mine can only be switched off by the main battery switch, so I'm living dangerously, I have to remember to turn the heater off, let it run til the fan turns off before turning off the main. Not an issue with the way I use my boat.

I don't understand why the insistence on outside air for combustion. The only thing I can think of is it lowers cabin pressure drawing in outside air, which might contain exhaust gases. I brought this topic up here before and no one had a good reason they thought of.

Most drip pot heaters draw combustion air from the cabin. Seems this is a good thing as you draw in some low humidity air from outside the cabin.

Don't follow internet advice, follow manufacturers recommendations, (unless you know more than they do)

Edit: Found my original post with this question
http://www.cruisersforum.com/forums/...ide-20734.html

[nigel1]

Instructions for my Air Top 5000 includes a dire warning on the dangers of suffocation if the combustion air intake is taken from the cabin.
Guess if you had the boat pretty well battened down it could happen.

Mine also has an inline 20 amp blade fuse

[GordMay]

With a direct-vent appliance, outdoor combustion air is drawn directly into the firebox through one pipe, while combustion products are exhausted through another (either coaxial or collinear).
This has two important benefits:
First, the sealed firebox generally makes these units safer: no room air is required for combustion, and will not spill or back draft byproducts of combustion into your boat.
In addition, because there is no loss of heated room air out the vent, the units are more energy-efficient.

[cal40john]

Originally Posted by GordMay

With a direct-vent appliance, outdoor combustion air is drawn directly into the firebox through one pipe, while combustion products are exhausted through another (either coaxial or collinear).
This has two important benefits:
First, the sealed firebox generally makes these units safer: no room air is required for combustion, and will not spill or back draft byproducts of combustion into your boat.
In addition, because there is no loss of heated room air out the vent, the units are more energy-efficient.

The Webasto comes with a 2 foot combustion intake hose and uses what appears to be a tight fitting fan to move the air through the box. I have difficulty seeing how the heater could continue to function and push exhaust gasses out of the intake hose. On the other hand, Dickensons were not sealed. The fan does not prevent backdraft out around the main intake, and there are other places where air comes into the heater, that can allow exhaust gasses out. You are also dependent on the natural draft of the chimney to pull exhaust gasses out as opposed to a positive pressure fan. Interesting dichotomy of the trusted Dickenson, versus insistence of the safest possible installation of something a lot less likely to have this problem.

Yes more energy efficient not bringing in the cold air, but we're on a small boat, producing water vapor by our bodies, cooking, etc. Most people argue that some air exchange is necessary to bring in cold outside air that will be low humidity as it warms up and is in addition displacing the high humidity air in the boat. It could be though that the amount of combustion air used by the Webasto is way more air transferred out of the cabin than is needed to reduce the humidity.