Boosting Webasto

[olam]

My heater is quite a long way aft in the boat and the hot air loses its flow rate
half way along the boat.
I have cut out some turns and insulated the pipes which helped the temp ,but still very low output.
Could i add an inline fan to boost the flow?Would it upset the heater?

 

[pvb]

An inline fan would be difficult to implement - doesn't your heater have different fan speeds? A better solution would be to increase the diameter of the ducting.

 

[Wunja]

How many vents do you have? You will probably lose half the flow with each vent. Adding an in-line fan between vents may start pulling cold air in through the vent rather than from the Webasto.

 

[johnalison]

Unless you have a leak, the same quantity of air must leave the pipe as enters it, so the length is immaterial as long as it it wide enough. Insulating the pipe may help.

 

[pvb]

Unless you have a leak, the same quantity of air must leave the pipe as enters it, so the length is immaterial as long as it it wide enough.

Not strictly true, even with bigger ducting there's a point where friction losses reduce the fan performance unacceptably, causing overheating.

 

[david36]

I have a notion that an additional fan would cause more problems than it solves. Unless you have a very long boat and/or too many sharp bends in the ducting, I suggest that you check that the output from the unit is at the correct flow rate. These things usually blow like a gale when going at full rate ie after they have warmed up and before the interior reaches the set temperature.
Fair winds.

 

[ghostlymoron]

It sounds like the problem is output from the heater rather than distribution. You could try de-coking with parafin as a first step.

 

[David2452]

To give any meaningful answer I would need to know the model, diameter of ducting (including intake duct), if reduced, number of outlets, Y pieces, reducers etc but what I can certainly say is that thermduct insulation has given material improvements every time I have used it. Fitting any kind of boost fan in line is not a place to start, if the ducting is properly matched to the model of heater with regards to length, number of fittings and outlets and lagged that is the way to go. One really good way to improve flow on long runs (but only if straight) is to use lagged thin wall ali pipe, it's actually cheaper than PEK too.

 

[alla_breve]

Just a thought- the cold air inlet to the heater isnt restricted?

 

[pcatterall]

To give any meaningful answer I would need to know the model, diameter of ducting (including intake duct), if reduced, number of outlets, Y pieces, reducers etc but what I can certainly say is that thermduct insulation has given material improvements every time I have used it. Fitting any kind of boost fan in line is not a place to start, if the ducting is properly matched to the model of heater with regards to length, number of fittings and outlets and lagged that is the way to go. One really good way to improve flow on long runs (but only if straight) is to use lagged thin wall ali pipe, it's actually cheaper than PEK too.

I have wondered about using smooth bore pipe but could never find the right diameter. It just seems to make sense that all those ridges on the normal ducting must upset the air flow.

 

[johnalison]

Not strictly true, even with bigger ducting there's a point where friction losses reduce the fan performance unacceptably, causing overheating.

That's why I said "as long as it is wide enough".

 

[pvb]

That's why I said "as long as it is wide enough".

Well, I suppose if you're suggesting unfeasibly big ducting, it could be true to say the length is immaterial. Within the parameters of boat installations, there are well-established guidelines on duct size, length, etc, as well as the effect of bends on resistance to airflow. Eberspacher have some excellent online reference material to help people plan suitable installations, but I haven't seen anything similar by Webasto.

 

[David2452]

Well, I suppose if you're suggesting unfeasibly big ducting, it could be true to say the length is immaterial. Within the parameters of boat installations, there are well-established guidelines on duct size, length, etc, as well as the effect of bends on resistance to airflow. Eberspacher have some excellent online reference material to help people plan suitable installations, but I haven't seen anything similar by Webasto.

We have a pionts system for fittings and duct design.

 

[pvb]

We have a pionts system for fittings and duct design.

Is that for Webasto, David? Is it online anywhere for people to refer to?

 

[olam]

Thanks for your replies.
Good point about the fan sucking in from other vents.
The piping is the right size,heater has been like this from new.
Heater is low in the lazerette,then runs under quarter berth to a y outlet,loads of hot air here.Then goes under galley/settee to another y outlet,not much force of air but still hot.then two tight bends to fore cabin,hardy any force of air but still hot.
All the pipes are lagged with the proper weabasto lagging.
No prob with the induction.
I disconnected the pipe under the galley yesterday it was like the wifes hairdyer,cound'nt keep my hand near it.
It just seems as though the friction in the pipes saps the flow rate.

 

[pvb]

Heater is low in the lazerette,then runs under quarter berth to a y outlet,loads of hot air here.Then goes under galley/settee to another y outlet,not much force of air but still hot.then two tight bends to fore cabin,hardy any force of air but still hot.

Do you have closable outlets at the quarter berth and galley? If not, these might be worth installing, so you can restrict the volume of air exiting. Cheap possible solution.

My Eberspacher has branching Y-fittings which have a reduced diameter duct to the outlet, which probably helps to maintain flow in the main duct. Don't know whether these are available these days (my boat is quite old).

 

[Vara]

Have you checked every inch of the ducting, I had a similar problem on the furthest vent, extracted duct and discovered a gaping hole where the duct passed under wardrobe, caused by pulling ducting against a bulkhead, bit of gaffer tape and flow restored.

 

[David2452]

Thanks for your replies.
Good point about the fan sucking in from other vents.
The piping is the right size,heater has been like this from new.
Heater is low in the lazerette,then runs under quarter berth to a y outlet,loads of hot air here.Then goes under galley/settee to another y outlet,not much force of air but still hot.then two tight bends to fore cabin,hardy any force of air but still hot.
All the pipes are lagged with the proper weabasto lagging.
No prob with the induction.
I disconnected the pipe under the galley yesterday it was like the wifes hairdyer,cound'nt keep my hand near it.
It just seems as though the friction in the pipes saps the flow rate.

That's a bit of help but specifics are needed really, what is the length of the induction duct? what is the model of heater? what is the dia and length of main feed and each branch and is any reduction involved on the branches,

 

[David2452]

Is that for Webasto, David? Is it online anywhere for people to refer to?

Webasto and Wallas Pete, I don't think its online, mind you people take no notice of even the available install manuals anyway so probably not a lot of point publishing it.

If anybody needs one I'm happy to provide it though.