Eberspacher ducting question

Bobc

Bobc

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I am just starting to fit a D4, and am trying to get my head around the ducting sizes to use.

The output port on the heater is 75mm, so I'm assuming that I'll want to use 75mm ducting for the main part, and possibly a smaller diameter as I get further away to add a bit of oomph to the air speed.

Are my thoughts right? It's just that in the instructions it mentions 90mm, but this doesn't seem logical to me if the port on the heater is only 75mm.

Also there's a chart showing values for each type of pipe and vent, and I can't get my head around this at all.

Any advice gratefully received.

Bob
 
Don't reduce the duct size - it has the opposite effect to what you expect. Keeping the maximum duct size you can all the way to the end of the duct is best. And when you T off, best to have a Y joint reversed to what you expect (think of a motorway - it should be like an on ramp, not an off ramp - that avoids dumping all the air at the early outlets). And insulate the duct - it improves output significantly.
 
I'd go along with the idea that the ideal duct will be pretty much the diameter of the fan assembly in the Eber. I liked the explanation of how to use swept tees in reverse!

I have major access problems in trying to get ducts forward of the quarter berths! I wonder, does anyone have experience of building cavities into the boat to use as ducts? It stikes me that a rectangular box section added to the front of the furniture would be much easier to accomodate than a paper tube.

Rob.
 
Bobc said:
I am just starting to fit a D4, and am trying to get my head around the ducting sizes to use.

Also there's a chart showing values for each type of pipe and vent, and I can't get my head around this at all.

Bob
Click to expand...
Bob,
I have just learned the hard way about the need to strictly comply with the air flow budget for an Ebers heater. The importance of this budget is not emphasised enough in the Ebers literature! Although Ebers give an example if you are lucky, their information is still hard to compute. Remember both cold 'in' & hot 'out' ducts contribute to the one budget allowance. Use no tight bends and/or elbows (one took me way over budget) unless absolutely necessary. If you need an second opinion on the final design, try posting the proposed sizes, lengths and split-points etc
Cheers (another) Bob
 
rob2 said:
I have major access problems in trying to get ducts forward of the quarter berths! I wonder, does anyone have experience of building cavities into the boat to use as ducts? It stikes me that a rectangular box section added to the front of the furniture would be much easier to accomodate than a paper tube.

Rob.
Click to expand...


Oddly enough I have, more than once, but on narrowboats where I used rigid ali tube boxed in and insulated. However, narrowboats are straight(ish), basically a box girder with windows cut out :) unlike marine craft where it would be difficult to use such a method except perhaps in certain sections, I would be concerned about using wooden boxes without internal lining and insulation due to the heat, BTW, P.E.K. duct is not paper and is designed to routinely carry 140c
 
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David2452 said:
I would be concerned about using wooden boxes without internal lining and insulation due to the heat, BTW, P.E.K. duct is not paper and is designed to routinely carry 140c
Click to expand...

Would that really constitute a fire risk? We've installed Webasto ducting without insulation (as it's in the first metre from the heater) running through a wooden bulkhead. I can't really think of any other option apart from suspending it somehow which is obviously not practical. Lining the hole perhaps?
 
Bobc said:
I am just starting to fit a D4, and am trying to get my head around the ducting sizes to use.

The output port on the heater is 75mm, so I'm assuming that I'll want to use 75mm ducting for the main part, and possibly a smaller diameter as I get further away to add a bit of oomph to the air speed.

Are my thoughts right? It's just that in the instructions it mentions 90mm, but this doesn't seem logical to me if the port on the heater is only 75mm.

Also there's a chart showing values for each type of pipe and vent, and I can't get my head around this at all.
Click to expand...

I'd seriously recommend that you look at the Eberspacher Marine Installation Manual and plan your ducting runs carefully. You'll probably find that 90mm ducting is essential to meet Eberspacher's airflow parameters. I'd also suggest you invest in a duct silencer - this makes a massive difference to the level of heater noise inside the boat.
 
catlotion said:
Would that really constitute a fire risk? We've installed Webasto ducting without insulation (as it's in the first metre from the heater) running through a wooden bulkhead. I can't really think of any other option apart from suspending it somehow which is obviously not practical. Lining the hole perhaps?
Click to expand...

Probably not but I wouldn't want to be the one to find out, yours is duct anyway not directly in a wooden tunnel so to speak, my concern would be the risk down the line after the wood had been constantly hot air dried out. I note that you say you have not used thermoduct for the first metre, this is the hottest part and you will loose heat that way, I have never understood why that is done, it certainly is not the offical line and I always use thermoduct right up to the heater outlet, even with the latest heaters which have a lower temperature limiter setting than the older ones I have never had an issue, if I ever did I would start with removing about 4" or so. I often do leave a 4" gap if running through lockers where bedding and clothing are stored though to give a little warmth in there.
 
RIBW said:
Bob,
I have just learned the hard way about the need to strictly comply with the air flow budget for an Ebers heater. The importance of this budget is not emphasised enough in the Ebers literature! Although Ebers give an example if you are lucky, their information is still hard to compute. Remember both cold 'in' & hot 'out' ducts contribute to the one budget allowance. Use no tight bends and/or elbows (one took me way over budget) unless absolutely necessary. If you need an second opinion on the final design, try posting the proposed sizes, lengths and split-points etc

Cheers (another) Bob
Click to expand...

What happened?
 
Talulah said:
You can different sized output ports for the Eberspacher.
The size required depends upon length of ducting runs.
My advice would be to get a 90mm cowling and only reduce down to 75mm where you 'T' off.
Ebay is usually a good source.

http://www.ebay.co.uk/itm/EBERSPACH...tEquipment_Accessories_SM&hash=item3f1a4fc747
Click to expand...

Flippin eck, assuming the Webo / Eber parts cost are on a par (they are usually not far apart) that is outrageous, mind you a lot of the duct fittings on eBay are, my dealer retail inc VAT on the similar Webo part is just over a tenner. Always check the dealer price for a benchmark price first.

Edit to say I was in error, the eBay price is on a par with Eber retail, still double the Webo bit though.
 
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Bobc said:
I am just starting to fit a D4, and am trying to get my head around the ducting sizes to use.

The output port on the heater is 75mm, so I'm assuming that I'll want to use 75mm ducting for the main part, and possibly a smaller diameter as I get further away to add a bit of oomph to the air speed.

Are my thoughts right? It's just that in the instructions it mentions 90mm, but this doesn't seem logical to me if the port on the heater is only 75mm.

Also there's a chart showing values for each type of pipe and vent, and I can't get my head around this at all.

Any advice gratefully received.

Bob
Click to expand...

The D4 air temperature is higher than some other heaters. The duct gets seriously hot. I used aluminium flexible duct then insulated it with 25mm foil faced mineral wool. My ducting is 80mm off the heater and I only use two discharge grilles. The first one in the saloon is 7"x2" double diflection grille. This has low pressure drop so moves an awful lot of air. The second grille is also a double deflection grill but a little smaller. I think if you have low pressure drop grilles that move a lot of air then you can get away with smaller ducts although I wouldn't like to go lower than 80mm. After my first grille I actually expand up to 100mm so that the second grille gets a reasonable amount of airflow due to the lower pressure drop. It works very well.
I don't have a duct silencer as the heater slow downs to a quiet speed once the boat is up to temperature. There is more of an issue with the exhaust noise. I am about to fit a second silencer to keep this external noise acceptable.
 
Thanks all.

So what I'm reading into this, is that the smaller the pipe, the greater the back pressure produced, which is a bad thing? It sounds like it's about keeping the ducting as big and straight as possible.

The main area that I want to heat is (obviously) the main saloon, so would the following thinking be about right?-

90mm ducting from the heater in the sugar scoop, forward under the aft berth and the heads and into the saloon and onto the forepeak as a backbone. Then a T in the saloon with a 90mm open vent. Then 2 take-offs from under the aft berth for both aft cabins with closeable vents (75mm), and a closeable 75mm vent in the forepeak.

Looking at the Eber manual, it suggests that only the ducting to the open vent is counted in the calcs. Does this mean that as far as the calcs are concerned, I can ignore the other vents and bits of pipe in the system?
 
Bobc said:
Looking at the Eber manual, it suggests that only the ducting to the open vent is counted in the calcs. Does this mean that as far as the calcs are concerned, I can ignore the other vents and bits of pipe in the system?
Click to expand...

I can't speak to the Eber manual but that certainly is not the case with Webasto or the others where a points system is used for the whole system i.e. every fitting, metre of duct and bends in the duct are designated points which must not exeed a given level for the install to perform at its best. It may be that the Eber values are given to the open vent more as a preventitive against overheat than as a full efficient system design.
 
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Bob,
as declared, I am no expert (in fact a proven failure) but here is my 2p worth.
Bobc said:
So what I'm reading into this, is that the smaller the pipe, the greater the back pressure produced, which is a bad thing?
YES
It sounds like it's about keeping the ducting as big and straight as possible.
YES

90mm ducting from the heater in the sugar scoop, forward under the aft berth and the heads and into the saloon and onto the forepeak as a backbone. Then a T in the saloon with a 90mm open vent. Then 2 take-offs from under the aft berth for both aft cabins with closeable vents (75mm), and a closeable 75mm vent in the forepeak.

Looking at the Eber manual, it suggests that only the ducting to the open vent is counted in the calcs. Does this mean that as far as the calcs are concerned, I can ignore the other vents and bits of pipe in the system?
YES
Click to expand...
From the most recent source I can find
http://www.espar.com/www/espar.com/tech_manuals/product_catalogue/Product_Catalogue_Jan_2013.pdf
Pages 70 & 71, The allowance for the D4 is '3' for 75mm ducting and '10' for 90mm ducting.

A 3m run of 75mm from the stern to saloon would exceed the budget once grilles are fitted.

Using 90mm, it looks like you can afford an inlet (cold) and outlet (hot) grille and a 6m run to the saloon.
Over to others to do a sanity check on these numbers
 
Bobc said:
Thanks all.

So what I'm reading into this, is that the smaller the pipe, the greater the back pressure produced, which is a bad thing? It sounds like it's about keeping the ducting as big and straight as possible.

The main area that I want to heat is (obviously) the main saloon, so would the following thinking be about right?-

90mm ducting from the heater in the sugar scoop, forward under the aft berth and the heads and into the saloon and onto the forepeak as a backbone. Then a T in the saloon with a 90mm open vent. Then 2 take-offs from under the aft berth for both aft cabins with closeable vents (75mm), and a closeable 75mm vent in the forepeak.

Looking at the Eber manual, it suggests that only the ducting to the open vent is counted in the calcs. Does this mean that as far as the calcs are concerned, I can ignore the other vents and bits of pipe in the system?
Click to expand...

I would be happy with that setup.
On a side note the Eber ducting has a limited life. We replaced with Silicone Heater hose (off ebay). Significantly more expensive but a fit it once and forget solution.
 
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