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Old November 26th 04, 07:29 AM
Gould 0738
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Default Let there be heat!

Finally finished that forced air furnace installation.

For either person who might have followed my progress through the first two
installments, here's the third, (and thankfully final) item in the series.

It works! :-)


Webasto Blue Heat, Part III

"Let There be Heat!"

(We've been reporting on a new do-it-yourself heater installation kit by
Webasto. The project has involved replacing an existing, 20-year old diesel
furnace on our Sundowner Tug, "Indulgence". Previous issues have detailed the
planning process preceding the installation, removing the old heater, mounting
the new Webasto Air Top 5000 on its bracket, and configuring the exhaust

I was slightly discouraged with the amount of time involved with getting the
heater mounted, swapping out the through hull, and creating the exhaust system.
It seemed questionable whether we would have our new diesel furnace installed
before spring. The fuel system, wiring, and ducting yet remained, and
experience with other projects has shown that fuel and wiring issues can be
more complex and time consuming. Any number of false started, trial and error,
mistaken processes seemed likely, but I was about to discover two of the
greatest benefits of Webasto's do-it-yourself kit. Although the fuel and wiring
systems would be the easiest portions of the job to foul up, Webasto's kit has
simplified the connections. Even a stumblebum such as I can complete the more
technically complex portions of the installation with only basic mechanical
skills and simple tools.

Fuel System:

The do-it-yourself kit includes a new dip tube and fitting that is intended to
be installed on the top of the fuel tank. Webasto warns against installing a
"T" fitting in a fuel line to a main engine or generator. Instructions state
that the Air Top 5000 may not function reliably without a dedicated fuel
source. Following the instructions, exactly, would have been difficult aboard
"Indulgence," as there is no practical access to the top of the fuel tank-
especially with sufficient vertical clearance to insert a 30-inch dip tube.
Disassembling the boat to reach the top of the tank would have been absurd. The
old furnace had worked for twenty years with a "T" fitting, but I wanted to set
up a system that would comply with Webasto's requirement for a dedicated fuel
source. The solution, while somewhat unique to "Indulgence", proved to be
easily apparent after only a few minutes of consideration.

Our boat loads heavy on the starboard side. There are several hundred pounds of
batteries and about 200 pounds of tools and spares that stow most logically on
the starboard side of the design. The helm and the majority of cabin fixtures
are to starboard, and as a result "Indulgence" can list just slightly to
starboard without some correction. As we have a single engine and two fuel
tanks, we set the valves on a fuel manifold to draw down the starboard tank
faster than the port. Either tank will supply more than a sufficient volume of
fuel to the engine underway.

By adopting a policy of shutting off the port tank at the fuel manifold before
running the Webasto, we can comply with the caution against sharing a fuel line
with another system.
The "T" fitting is between the port tank and the fuel manifold, so when the
manifold valve is closed the port tank is entirely dedicated to the Air Top
5000. The fuel management policy satisfies the operational requirement of the
Webasto furnace without requiring a major refit. As with several aspects of our
specific "retrofit", this adaptation may not be practical on all vessels.
Boaters with better access to their fuel tanks would be well advised to install
the Webasto fitting, a process that the directions indicate should be simple
and straightforward.

Webasto furnishes a modular fuel pump assembly with the Air Top 5000. The
12-volt pump and a filter are mounted in a metal case, with "in" and "out"
compression fittings.
The pump makes a pulsing noise when operating, and rubber sound isolators are
recommended when attaching the pump to a bulkhead or floorboard. One of the few
disappointments with the do-it-yourself kit was that many of the small parts
were sacked up willy-nilly and not always separated by system. Webasto
furnished four mounting "legs" for the fuel pump, but I failed to find them (or
to realize what they were), until I had fashioned a mounting plate from a bit
of scrap sheet metal stock.

The fuel pump can be mounted on a horizontal surface, and may be mounted
vertically providing the "out" fitting is at the top of the case. Mounting the
pump upside down could create an opportunity for air bubbles to form in the
fuel line and interrupt the supply of fuel to the furnace. We mounted the fuel
pump horizontally, behind the engine room ladder and less than a foot from the
"T" fitting.

Rigging the fuel line was extremely easy. Our old heater had a plastic fuel
line, which has to rank among the more unsafe practices in an engine room. A
plastic line could burn through in a matter of seconds and literally pour
diesel into the flames. The ABYC compliant fuel line for the Webasto is a
length of copper tubing. Connections were made with compression fittings or
some specialized rubber hoses and clamps supplied by Webasto. I added an
optional, additional filter jut beyond the "out" port of the fuel pump case,
routed the fuel line under and behind some bracing structures where it would be
protected from careless tool use in the engine room, and connected it to the
fitting on the
Air Top 5000. It would have been an auspicious day to buy a lottery ticket;
when I opened the valve that connected the Webasto pump to the fuel system, all
the connections on the non-pressurized side of the pump proved to be properly
done. I wouldn't know about the pressurized side of the system until I actually
activated the pump and ran the furnace, and that would need to wait until
several additional steps were completed.


The Webasto kit makes wiring the Air Top 5000 extremely simple. The
instructions could have been slightly more explicit regarding the connection of
the small, fuel pump control circuit plug on the wiring harness. All wiring
connections to the furnace proper are located under a removable plastic cover.
The main harness connection is obvious, but the smaller receptacle for the pump
control circuit is concealed under a removable rubber plug. Once the fuel pump
control circuit mystery was resolved, there were only five other very simple
connections to accomplish.

The Webasto wiring harness separates into two branches just beyond the furnace.
One branch is routed to the Webasto control module, and simply plugs in to
connect. We located the control switch near the helm. The do-it-yourself kit
does not include a thermostat, but rather a rotary switch with an infinite
number of positions between
"Low" and "high". The wiring harness does have some "extra" wires that could be
connected to an optional thermostat, but they aren't needed for a complete and
properly functioning installation.

The other branch of the main wiring harness is routed to the "house" battery
The brown wire connects to the negative side of the battery, and the red wire
connects to the positive. The red wire has an inline fuse holder, and Webasto
includes the fuse with the kit.

The power supply circuit to the fuel pump connects to a pair of leads that
protrude from the bottom of the Air Top 5000, literally routed through the
combustion air intake port.
Webasto ships the unit with some tiny "alligator" clips on the end of the wires
protruding from the furnace, and the female end of a specialized plastic
fitting on the power supply wire connected to the fuel pump. The connection
seemed tenuous, to me, and I also had roughly six feet of excess cable between
the furnace and the fuel pump. I cut away the extra length of fuel pump wire,
cut off the alligator clips, and used butt connectors instead.


There are four types of intake and exhaust considerations required for a forced
air diesel furnace: combustion air intake, combustion exhaust gas removal, heat
duct outflow, and cold air return. The exhaust system had been installed just
after mounting the furnace on its bracket. (See last month's issue)

Combustion air can be introduced via a through hull fitting, or simply drawn in
from the bilge. I had hoped to bring in outside air, but couldn't clear the 18"
radius that Webasto recommends between the exhaust through hull and a
combustion air intake through hull. Moving the combustion air intake 18"
forward would put it in a location closer to our bow wake than I thought
advisable. Moving the air intake through hull 18" aft of the exhaust fitting
would put it in an inaccessible location behind the port fuel tank. We finally
opted to take combustion air from the bilge, and installed a special section of
short, double walled hose that Webasto supplied for that purpose. The double
wall hose construction is intended to reduce airflow noises.

The cold air return was an interesting retrofit. We used a section of the cold
air return from our old system, which proved to use a different diameter of
duct hose than the Webasto. Sure Marine supplied a specialized "Y" that made
the adaptation possible, but would not have been required in a from-scratch
installation. The "Y" was one of only a few items needed to complete the
installation that weren't included in the kit, and all the rest were extremely
incidental or were specialty tools, (such as hole saws), that many people would
already own.

Many boat-heating experts suggest a cold air return system that provides a 70%
"recycling" of previously heated cabin air and introduces 30% of the air from a
source outside the boat. We converted an extra engine room vent to the outside
air source for the Air Top 5000. There is a danger of bringing rainwater or
even seawater into the heater with an outside source, so we fashioned a deep
"belly" in the intake hose immediately after it routes aboard, and drilled a
small hole in the bottom of the belly for drainage. There isn't a way for me to
measure the exact ratio of recycled interior vs. exterior air, but the
decreased amount of airflow (and noise) through the old cabin air intake
encourages me to guess it may be close to the 70/30 ratio often considered

All of the cold air return and hot air ducting was easy to assemble. It took as
long to plan the exact route of the hot air duct and drill three new holes for
outlets as it did to actually assemble the duct. Our old furnace had been
installed on some theory suggesting that turning the forward cabin into an oven
might accidentally warm up the main and aft cabins as well. Our new Webasto
connects to two new vents: one under the dining table in the salon and the
other in the forward bulkhead of the aft cabin.

The first moment of truth:

Approximately fourteen do-it-yourself installation hours had been invested
removing the old heater and installing the new Air Top 5000. The time was at
hand to see whether the time had been well spent, or whether portions of the
job would need to be redone. I inserted the fuse in the positive battery lead,
climbed up to the salon, and twisted the control knob to the right. A green
indicator light in the center of the knob illuminated to assure me that there
was DC current to the control switch: a positive beginning.

A barely perceptible "tick-tick" emanated from the fuel pump, confirming that
it had power as well. A slightly discernable draft in the cabin air intake
fitting indicated that the heater fan was also working. Preliminary electrical
indications all seemed OK.

I climbed back down the engine room hatch to check the pressurized side of the
fuel pump. Nary a drop, all connections proved sound and solid. After a few
minutes, the furnace fan speed increased considerably. A good quantity of cold
air was blowing through each of the three heat vents. Then, the system shut
down without lighting.

Had I not read the instruction manual, I might have erroneously concluded that
there was a problem with the heater. (Or, far more likely, my installation).
Webasto's manual warns that the furnace may not light on any of the first
"several" attempts after initial installation. It takes a few start-up attempts
for the fuel pump to purge all the air from the fuel supply line. The longer
the line, the greater the number of attempts required.

Each time the system failed to ignite, I would turn the control knob back to
the "off" position, wait for a minute or so, and then crank it back to full on.
On the third startup attempt, the Air Top 5000 fired up and heat began flowing
into all three cabins. Yes!

The second moment of truth:

Just as my arm began to cramp up from self inflicted back patting; the heater
shut down prematurely. "Maybe there was an air bubble in the fuel line," I
thought. "I'll try it again." On a second attempt after the initial firing, the
heater also ran for about ten minutes and then shut down. On a third, the same
results. Clearly there was a problem, somewhere. What had I done wrong?

An incidental glance at the DC distribution panel provided the answer. On a
dark November day, I had almost every cabin light in the boat turned on,
including some larger wattage DC bulbs in the engine room, to provide enough
light for ease of working. The AC battery charger breaker had been accidentally
bumped into an "off" position who knows how many hours before. Battery voltage
was down to just barely above 12. On the basis of a calculated guess, I ran the
main engine for a few minutes until DC voltage had returned to a point just
below 13-volts, and then fired up the Webasto again. The system worked
perfectly, and I shut it off at the switch about 45-minutes later.


The Webasto do-it-yourself installation kit absolutely enables a novice to fit
a forced air diesel furnace to a boat. With nearly all the parts and pieces
needed for the job delivered in a single box, a simplified wiring harness, and
a pre-engineered fuel pump assembly, many of the more difficult technical
problems have been solved. There are a few minor issues with Webasto's
presorting and sacking of parts, (I think they should be sorted and sacked by
system), and a few portions of the instruction booklet could have been more
precisely worded or illustrated. Unless a boater is certifiably dangerous
around simple tools and low voltage wiring, the kit brings the installation
process within the reasonable abilities of most amateurs. (Exactly as
demonstrated by yours truly, a semi-klutzy mechanical amateur).

Projects such as this often inspire greater respect for the professionals in
the trade.
A heater installation involves the fuel system, the electrical system, and a
fair amount of mechanical fitting aboard a boat. As a do-it-yourselfer I had an
advantage: I was already very familiar with my own boat. Taking a heater aboard
an unfamiliar craft and accomplishing a good installation would be no simple
task, and would require a broad technical understanding of marine systems. I
learned a lot during the heater project, enjoyed the satisfaction of building a
functional system, and can recommend the Webasto
self-install kit to other boaters open to an interesting and rewarding, very
doable, challenge.

Thank you:

Special thanks to Sure Marine in Seattle for providing me with the opportunity
to test and review this self install kit. And, of course, thanks to Webasto as
well. The Air Top 5000 is proving to heat the boat quickly and evenly, and
operates with much less noise than the old unit it replaced. A great product,
and an exceptionally enabling kit. (If I had tried to do this without the kit,
it really would have been next spring before we got heat back aboard

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Old November 27th 04, 03:31 PM
Posts: n/a

Excellent article Chuck. Thanks very much!

Gould 0738 wrote:
Finally finished that forced air furnace installation.

For either person who might have followed my progress through the first two
installments, here's the third, (and thankfully final) item in the series.

It sounds like you installed the new heater with an in-line fuse... does
it not have a breaker on the panel? I added a set of three new breakers
to our panel, two are for the heater & it's fans; the third is yet
unclaimed. How was the old heater wired in?

BTW I don't know if I mentioned our issues with installing the exhaust
system piping on our heater- it was the most expensive & time consuming
& irritating part of the project. Eventually I called in a welder, an
expert marine fabricator who did a beautiful job putting the pieces all
together... and with every bit of it welded, there is zero possibility
of a CO leak...

I don't understand how so many people cruise without heat. It's
miserable to be cold, even worse when you're wet too.

Fair Skies
Doug King

  #3   Report Post  
Old November 28th 04, 10:42 PM
Gould 0738
Posts: n/a

I don't understand how so many people cruise without heat. It's
miserable to be cold, even worse when you're wet too.

Fair Skies
Doug King

We just spent two nights a Pouslbo. It got down to freezing Saturday night. Ran
the Webasto, as there was nobody alongside where the exhaust was going, and the
boat could be described as "toasty".

There is a little less heat going to the forward cabin than I would prefer, and
a bit more available in the aft cabin than we really need, but I have a couple
of ductwork tweaks in mind that should reallocate the air flow.

It sounds like you installed the new heater with an in-line fuse... does
it not have a breaker on the panel? I added a set of three new breakers
to our panel, two are for the heater & it's fans; the third is yet
unclaimed. How was the old heater wired in?

The old heater was wired directly to the battery, with a fuse located at the
heater itself.

The simplified wiring is one of the features of the do-it-yourself kit. If the
same heater is sold to somebody who is supposed to know what they're doing-
there is a "pre-wire" board available (essentially a combo bus and circuit

  #4   Report Post  
Old November 29th 04, 02:02 AM
Posts: n/a

Only works in port and with shore power.....but an 110 v electric blanket
can work wonders on a chilly night. Low cost and light weight. See your
favorite Wal-Mart for about $30 to $60.00 depending on size and features.
RichG manager, Carolina Skiff Owners Group on MSN

  #5   Report Post  
Old November 29th 04, 02:41 AM
Posts: n/a

On Mon, 29 Nov 2004 01:02:48 GMT, "RichG"

Only works in port and with shore power.....but an 110 v electric blanket
can work wonders on a chilly night. Low cost and light weight. See your
favorite Wal-Mart for about $30 to $60.00 depending on size and features.


With an inverter and decent battery bank (4 golf cart batts) you can
actually run an electric blanket all night long while anchored out.
We found that it made all the difference with late season cruising in
the north east. In the morning we'd fire up the generator for an
hour, recharge the batteries, make some hot water for showers and heat
up the cabin with reverse cycle A/C.

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