Webasto Airtop 2000st
installing into a camper trailer

introduction

Being born in a sub-tropical island, anything below 25 degrees is on the fresh side and anything below 20 is on the freezing side for me. So the extension of bush camping, the form we prefer, beyond the summer months had to involve some form of heating. I have tried several systems ranging from the Zodi gas heaters (a gas heat exchange system no longer manufactured and in any case not approved in Australia as far as I know) to the Coleman catalytic gas heater. These were OK additions but nowhere near the necessary heating level I wanted nor the safety I would be comfortable with for leaving it running all night. I wanted to be sure that the combustion part was completely separated from the heated air sent to the living area. This is why I finally decided on making the expense of a cabin diesel heater and we have been delighted with the result.

Having a diesel powered car and only two 4.5Kg gas bottle holders on the camper trailer, plus the lower cost of fuel per unit of heat, the choice was easy for me between diesel and gas, but this is really a case by case decision. The key is to enjoy the outdoors in the colder months. Since I enjoy the DIY side of things too, I could install the diesel heater myself without requiring the services of a third party for the gas connection. The unit was more than powerful enough for heating up the sleeping section of our 12" tent in humid +3 degrees nights we had near Tassie's highland lakes in late April.

I bought a Webasto Airtop 2000ST unit from a distributor in Sydney about a year ago (transacted over this famous auction site for around $1300) and I have to say this has been the best investment made as an addition to our camper trailer. The Webasto kit is very comprehensive but is a general kit meaning it is suitable for RVs, cars, trucks and boats and therefore you will have a few spare parts left at the end. On the other hand there are a few extra items necessary for the campertrailer mounting but this is all available from local stores. I have made a list of these items at the end of this how-to.

I suspect an EBERSPACHER unit would mount the same as they look strangely similar.

The operation of the unit is pretty simple since there is a thermostat (supplied) that controls the temperature and determines the starting and stopping of the burning in the unit, and in between, the regulation of the heating rate. I describe below how the unit works in the context of a camper trailer as this was not obvious to me until I run it. The benefits are of course keeping the sleeping area and the annex warm but also drying the canvas when dew or rain makes it damp or wet. Alternative uses include: cloth dryer and hair dryer (imagine a 2000 watts hair dryer for your better half), and many more uses I am sure.

key considerations before buying/installing

1. Where to mount the unit. The key consideration here was where will the heated air be directed to. In my case I found that under the bed, on the articulated side, and just in front of the kitchen was the most practical for sending the hot air either to the annex (nice for a comfy breakfast in the morning), or to the bedroom by just moving the short flexihose. Also consider other items in the trailer for physical interference, in my case the swing-out kitchen. Noise from the unit itself is also to be considered, with a simple barrier (e.g. the wooden bed base) being sufficient.

2. The path from the fuel tank to the heater and what type of tank (Jerry can or permanently dedicated tank).

3. The path of the combustion air inlet and exhaust, the placement of the fuel pump and their protection from external elements (rocks, dust, water).

4. The 12V electrical source. The maximum current consumption is around 2A once started, therefore a 10 hours overnight run will use 20AH at full power. In my experience expect between half and 2/3rds of this since the heater adjusts the power down when the temperature reached the desired value. The maximum current at start and stop of a combustion cycle is 7A for approximately 2 or 3 minutes. And this should happen only once or no more than a few times per night. So most batteries found in CTs will be more than capable enough if charged properly the day before.

Care must be given to the 12volt power supply circuit: it is best if the heater’s supply wires are connected directly to the battery as the unit checks that the battery voltage is not too low to prevent damage by over-discharging. If not connected directly, the additional supply cables need to be of sufficient section to minimize the voltage drop especially during start-up (7Amps draw).

5. Re-circulating or fresh air input. Fresh air input means that the clean air which passes through the unit and is then sent to the living areas is not taken from these areas but from the outside. The benefit is a simpler installation (only one flexihose to worry about) at the slight cost of extra fuel consumption since the outside air is colder than the one in the heated area. Using fresh air also means that a separate temperature sensor is required since the unit normally measures the room temperature in the return circuit. I describe below how to add this sensor without breaking the bank.

Noise is an aspect that needs attention since the primary application of such devices is on motor vehicles in cold countries or in RVs with a solid shell. The canvas does not provide much of a sound barrier and after the initial tests in the field I made a few modifications and enhancements to alleviate this issue. We now have a very silent heater, making less noise than an electric fan heater when we are in bed and not producing annoying noises for the neighbours.

The noise sources are:
a) The burner's noise (like a 747's reactor - in reduced version of course)
b) The noise of the burner's inlet fan
c) The hot air fan (the one that pushes the air in the CT).
d) The fuel pump. This is a piston dosing pump meaning that is produces a “tock” noise every second or two depending on the heating rate. The mount supplied is ok for an RV but not for a canvas CT in my opinion.
e) The noises inside the unit itself (fans mainly and combustion).

the installation

I have installed the unit in the trailer below the articulated side of the bed and towards the back (just in front of my tailgate kitchen). See pictures above. That way I can direct the air either in the bedroom or in the annex just by moving the flexihose around. As I have small zippers in the corners where the PVC floor joints the bed, I simply pass the flexihose though one of those for when we sleep.

Mounting the unit under the bed means that its noise proper is pretty much eliminated, and the following was done to reduce the noise sources mentioned above:

1. I installed the supplied burner's exhaust silencer and added the maximum length of pipe to eject the fumes to the opposite side of the CT (on the opening side of the bed base). The exhaust pipe passes under the trailer behind the water tank and is simply made of the outside pipe of long galvanized tent pole, cut at the extremities. This joins perfectly with the stainless steel exhaust hose supplied. The length and the direction of the exhaust mean we barely hear the "747".

2. I have fabricated and added in the combustion inlet a silencer made of PVC pipe and foam (like a muffler). This silencer is only about 25CM long but does reduce the inlet noise quite significantly. See the pictures below which describe the parts required. The end caps are PVC water pipe caps (from your preferred hardware store) and glued using water pipe glue (acetone based I think). The internal wall of the pipe section is laid with a piece of sound deadener sheet from Jaycar (part no. AX3689) and the labyrinth made of pieces of the same sheet. They are glued using contact glue.

The entry and exit of the inlet pipe (the little back flexible hose) in and out of the muffler are sealed with silicone to ensure good sound proofing. There are commercial variants of these mufflers for the Webasto units.

3. I have made out of a 7cm length of 50mm PVC pipe and some high temperature foam a silencer/reducer for the hot air outlet (the one in the CT) that I can insert or remove as needed. If I want full output for a quick heat-up or for drying the tent I leave it out, and I insert it before going to bed. This reduces the fan noise but also slows the flow of heated air and forces the unit to reduce it's burning rate further which in turns reduces the noise even further.

4. I placed the fuel pump inside the front tool box to separate it from the rest of the trailer since it vibrations can be transferred to the trailer box itself and resonate though. I made it completely silent by wrapping it into a complete sound deadener sheet from Jaycar (part no. AX3689) and added a small fuel filter for good measure.

Note that the normal mounting of the fuel pump is on the outside of the trailer as are the combustion inlet and exhaust pipes.

To protect the fuel lines when passing outside the trailer’s body I inserted the supplied hard plastic pipe (around 4mm diameter) into a 6mm windscreen wiper’s water pipe and then into a split-tube loom tube (both from your preferred automotive accessory shop). If required, a fuel pipe from the same shops will provide extra protection for the fuel line as they are reinforced. I used glands for the entry and exit to/from the tool box to keep it water and dust proof.

I had to fabricate a protective plate for the inlet and outlet pipes as they are on the outside of the trailer and could be damaged by flying rocks. This was done with a piece of 1.5mm aluminum checker plate from a hardware store. It is used as a backup plate for the heater, therefore I did not use the supplied backup plate.

I paid attention to the space around the combustion hose as it gets very hot and is necessarily on the outside of the trailer. Children could get burned and the PVC floor of the soft floor camper could get damaged if there was contact. In my case, the combustion inlet and exhaust are hidden behind the PVC where it joins the bed base, with about 15 cm clearance between the hot pipe and the PVC.

I also found out that the fuel pump is very powerful and will bend the tank in (even a metal jerry can) if no breathing of air is allowed in. I made a fuel pickup cap from a jerry can nozzle and used two part epoxy tank repair compound to fill the end (see Picture), then sealed with black silicone.

One note: the first time the heater is started it will take some time for the fuel line to be purged of air and this will require several start and stop sequences (about 6 or 8 from memory in my case), so be patient. If there is a bit of air left in the fuel filter placed before the pump, it does not seem to alter the working of the unit.
 
how it works

The heater works the following way from what I have observed: When the thermostat is turned from the OFF position to a certain temperature the unit will start it’s fan at very low speed (almost inaudible).  If the air temperature is or drops below the set temperature it will initiate a heating cycle.

This means that it will purge it’s combustion chamber first for a minute or so and then start it’s hot surface (like a glow plug) and start the pump to inject diesel in the chamber. During these 2 or 3 minutes the 12V current consumption is around 7 Amps. Once the combustion is started (the 747 like noise becomes noticeable), it will switch off the hot surface and the current will drop to about 2 Amps. At this point it produces about 2KW of heat and the air fans are at maximum speed.

Once the air temperature gets close to the set temperature of the thermostat, it will reduce its heating rate to maintain that temperature. The minimum it seems to be able to run at is just under half of full heat (about 0.9KW). At this point it has reduces it’s fan speed quite a lot and the noise level has reduced significantly as well. The current consumption is around 1.1 Amp at that seems to be the standard running for our unit during the night.

If the temperature get above the set point or the thermostat set point reduced enough, or the thermostat turned to the OFF position, the unit will initiate a burner shutdown by stopping the fuel pump then lighting up the hot surface again (7Amps during that time) for about 2 or 3 minutes to purge the combustion chamber of fuel. Then it will only run the fans to cool down the unit for 3 to 5 minutes before going back to a very low standby fan speed or shutting them down completely (thermostat in the OFF position).

The fuel consumption is very reasonable and my 20L jerry does lasts over a week with around 10 hours of runtime per day (we keep it ON all night).

I never had an issue with fumes as the only time I can see diesel fumes is when the unit initiates or terminates a heating cycle. Since these should be kept to a low number (ideally once or at most a few times a night) this should not be an issue. During normal running, there is only humid hot air but no visible fumes coming out of the exhaust. Furthermore with the exhaust being brought right back to the outside of the trailer with the long exhaust pipe it should not normally smell at all in the sleeping section.

conclusion

The whole installation was relatively strait forward with only the noise reduction requiring extra work. If I had to re-do it again the only change I would make would be to mount the fuel pump inside a small box (aluminium toolbox for example) behind the jerry can, instead of using the front tool box to house the pump. This would have reduced the amount of fuel line routing I had to go through.

With winter coming, this is a great project to extend the camping season.

No link to any of the companies/brands, just a warm happy camper.

This is just meant as an example of what can be done as I am no expert in the matter. Please seek advice before installation.

list of materials & costs

1 x Webastor Airtop 2000ST (around $1,400 these days on “that auction site”, plus about $50 transport).
1 x 1.5 mm aluminium check plate if external protection of inlet, outlet or pump is required – approx $25
1 x 1 metre of 50mm white PVC pipe, 2 x end caps, PVC glue, contact glue, part of 1 x sound deadener sheet from Jaycar (part no. AX3689) – say $40
1 x long galvanized tent pole for exhaust extension (if required) – approx $17
1 x tiny fuel filter (have been known to be supplied in some kits) - $9 from Autobarn
1 x sound deadener sheet from Jaycar (part no. AX3689) or the leftover of the one above for the pump noise reduction. $29
1 x length (as required) of wiper’s water pipe (black from an automotive accessories shop), 1 x length (as required) of split-tube loom tube (from same shop or Jaycar) – approx $30
Cable glands as required for fuel line and fuel pump electric cable if mounted in a water/dust proof box – approx $25
1 x tank or jerry can. Plastic is fine, making sure it can breathe while the heater is running – approx $30

how to make & wire an external temperature sensor

This is necessary if the heated air is not re-circulated (i.e. fresh air is used), as the heater normally measure the living air temperature by the return air circuit. Two wires (one yellow, one black and blue) are visible near the thermostat on the wire loom. They are connected to a fixed resistance inside a small rubber cover.

Simply cut the wires and replace the resistance with a 10KOhms NTC thermistor (Jaycar part number RN3440 at $1.35). Insulate both wires of the thermistor and add a layer of insulation around the thermistor to provide a bit of protection and temperature sensing lag. This may void the warranty so there is a Webasto external temperature sensor available too.

I have mounted the thermostat in one corner of the wooden bed base and the thermistor is mounted at bed level since this is the temperature we want to keep constant.

This is just meant as an example of what can be done as I am no expert in the matter. Please seek advice before installation.

 thanks to John Douyere for sharing this idea

may2011