Boiler Insulation (Duetto Steam Boiler)

by Mole : 25th August 2008

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Issue: Having a non-insulated boiler in an espresso machine, especially the steam boiler, is wasteful of electricity and causes internal components to run hotter.
Solution: Find a (cheap) temperature stable material and insulate the boiler.

For more information, read on…

History of the Issue

Like many espresso machines, the original batch of the Izzo Alex Duetto came without insulation on either boiler. Whilst we are not yet convinced of the effect of insulating the PID controlled brew boiler, it is certainly worth insulating the much larger, hotter, steam boiler. To leave any espresso machine without insulation on the steam boiler (or single boiler of an HX machine) seems very wasteful of electricity. Also, all that extra heat inside the machine cannot be good for the internal components. The simple answer: Insulate that boiler!

Note for Duetto owners with insulated steam boiler: It seems that newer Duettos are coming with insulated steam boilers. However, this appears to be just a wrap-around foil-backed insulation. Whilst this must help to reduce wasted heat and power usage, it would still be a good idea to add pieces of insulation to the top of the boiler, following the process in this article.1



DaveC used a polyester Christmas tree snow skirt ( to insulate his Alex MKI boiler. He went from a duty cycle of 23% (heating element on for 15 seconds, off for 50 seconds) to just under 8% (element on for 14 seconds, off for 165 seconds). A great improvement, though the pre-insulated duty cycle seems a bit high to me. Paul L used a polyester batting made for furniture upholstery ( which was tested to be good to much higher temperatures than your average steam boiler. He went from a duty cycle of over 13% to just under 7% - again, a great result.

Unfortunately, I could not easily find the polyester batting that Paul L used (the shop appeared to have closed down). DaveC had the bright idea of using 'pond liner underlay'. This is a synthetic polyester fleece, around 3mm thick, and should be available from most aquatics centres. I was dubious, but DaveC persuaded me to try it. Ask them to cut you £3 or £4 worth from the roll (huge roll they will have outside), as the previous cut is usually not straight and can be ragged, you will get enough insulation material to do your boiler nearly 3 times over!

It is not thick enough to be very effective as a single layer, but used as a folded triple layer it works extremely well. Along with wrapping it around the steam boiler, you should also insulate the very top of the boiler, including the pipes. Basically, leave only the vacuum breaker and safety pressure relief valve showing, and cut a slit to place around the autofill probe. Here are some pictures of the installation in my machine… (click on the pictures to enlarge)

1_Overview.JPG 2_FromBelow.JPG

In the first picture we see an overview of the installation. You can just make out how the triple layer is wrapped around the boiler (lower arrow). To aid installation, we pierced a hole in the leading edge of the insulation and used a large cable tie to draw the triple layer around the boiler avoiding pipes and electrical wires. You could also use string or anything that will enable you to pull and push the instulation around the boiler. Needle nose pliers are also your friend! You can also see the top pieces (rough cut squares) which are tucked down inside the wrapped layer and have slits cut in (shown by the upper two arrows) to avoid the three important components on the top of the boiler which will need to protrude from the insulation. These are, from left to right: Autofill probe, pressure relief valve and the vacuum breaker valve.

The second picture shows how the triple layer looks from under the machine (with the front-most bottom plate removed). You can see the insulation wrapped around the boiler shown by the red arrows. There is no need to insulate the bottom of the boiler, which would be very difficult to do anyway, and so there is no need to remove this bottom plate.

3_FromTop.JPG 4_TopPieces.JPG

The third picture shows the square pieces cut to place under, around and over the pipes on the top of the boiler. In this picture you can only see the top-most pieces, which sit over the pipes and connections to the boiler. However, we cut some rough shapes to fit around and under the pipes before adding these final square pieces, which are neatly tucked between the boiler sides and the wrapped triple layer.

The final picture shows how the top pieces are tucked below any wiring and avoid the PID controller and relay box (arrow to the right). The arrow to the lower right identifies where the top pieces are wrapped around and under the pipes, whilst the final lower arrow shows the top-most square pieces which lie over the pipes.

Final Comments

A few weeks on and there is no sign at all of heat damage to the fleece, not that I expected any. It works incredibly well. Unfortunately, I did not really test the duty cycle before insulation, but my guess would be slightly lower than Paul L's observation, perhaps 10 to 12% or so. The power draw is probably lower than the standard heat exchanger Alex models, simply because the steam boiler in the Duetto does not heat the group (the brew boiler does this). Nonetheless, the steam boiler in the Duetto is only marginally smaller than the Alex MKII single boiler and runs at a slightly higher 1.4 bar. The duty cycle after insulation is very low: 3 to 4 seconds on for 60 to 80 seconds off. It is as close to 5% as it could be. Given it is about a 1500W element (European Duetto running on UK voltage of 240V), this equates to about a 75W steady state power usage from the steam boiler. I think it is fair to say that the polyester pond underlay works very well and is probably comparable to, or slightly better than, the other polyester materials that DaveC and Paul L have tried.

Even with both boilers running, the (insulated) Duetto's power usage is about 140W steady state as opposed to my old Andreja Premium's 120W. Not bad considering it has an extra brew boiler and larger steam boiler! It may be possible to bring this down to around 100W to 110W using insulation on the brew boiler, but we are not yet sure how well the PID controller would cope with this low a heat loss from the brew boiler. For reference, I normally run with the steam boiler off until I need it. With only the uninsulated brew boiler running (and keeping the group at perfect brew temperature) the Duetto uses about 80W in the steady state.