Domakihub How to Insulate a Hot Water Tank and Cut Energy Bills
A simple weekend job that pays for itself within months.
Reviewed by Domakihub home & decor pros · 2026-06-23 · 5 min read
An uninsulated hot water tank loses heat continuously through its metal shell, forcing your boiler or immersion heater to fire up more often than it should. The video above shows the fitting process in real time; the steps below give you the full picture — from choosing the right jacket to finishing safely — written for the cylinder-style tanks found in most Greek homes, holiday rentals, and small hotels. Done correctly, a tank jacket typically pays back its cost in three to six months on a typical Greek electricity tariff.
Why Greek Homes Lose So Much Hot-Water Heat
Many properties in Greece use a cylindrical boiler tank (μπόιλερ) mounted in a utility room, basement, or outdoor cupboard. These locations can swing from 5 °C in winter to 40 °C in summer, and most older tanks have little or no factory insulation — just a thin layer of foam that degrades over time. The result is standby heat loss every hour of the day, even when nobody is showering.
In a holiday rental or hotel with multiple tanks running year-round, uninsulated tanks can add hundreds of euros to the annual electricity bill. A proper insulation jacket, costing as little as €15–30, can reduce standby losses by 25–45 % according to UK and EU energy studies — a proportion that holds equally well in the Greek climate.
Choosing the Right Insulation for Your Tank
The most practical option for an existing cylinder is a pre-cut insulation jacket (also called a tank jacket or lagging jacket). These come in fibreglass or mineral-wool fill wrapped in a plastic outer skin, rated to specific tank diameters. For tanks that already have some factory foam but feel warm to the touch, a supplemental foil-backed foam wrap is an alternative that adds an extra thermal layer without bulk.
Avoid wrapping gas boiler tanks yourself without professional guidance — gas appliances have specific ventilation requirements. For electric immersion tanks (the most common type in Greek villas and apartments), a jacket or foam blanket is a safe and straightforward DIY project.
How to Insulate Your Hot Water Tank: 5 Steps
- 1
Measure your tank and buy the right jacket
Switch off the immersion heater or boiler and let the tank cool for at least an hour before you touch it. Measure the height and diameter of the cylinder with a tape measure. Most hardware stores (PRAKTIKER, Leroy Merlin) stock jackets in standard sizes; check the packaging label to confirm your tank falls within the rated range. A thicker jacket (80–100 mm) saves more energy than the thinner 25 mm entry-level options.
- 2
Clear the area and inspect the tank
Remove anything stored around the tank and wipe down the outer surface with a dry cloth. Look for any corrosion, damp patches, or signs of a slow leak — insulating over a leaking tank hides a problem that will worsen. If you find rust or moisture, call a plumber before continuing. Also note the position of the thermostat, the pressure-relief valve, and any pipe connections; you will need to cut or leave gaps around all of these.
- 3
Wrap the jacket segments around the tank
Most jackets come in two or more panels held together with straps. Starting at the bottom, press each panel firmly against the tank surface so there are no air gaps — air pockets trapped between the jacket and tank act as insulation, but large voids do not. Overlap the edges of each panel by at least 50 mm. Keep the top of the tank clear if it has a thermostat or anode rod access point.
- 4
Secure and seal the jacket
Fasten the manufacturer-supplied straps or tape around the circumference of the tank. Do not use ordinary parcel tape or gaffer tape as these degrade in a warm utility room. If the jacket does not include straps, use purpose-made foil tape rated for high-temperature use. Cut neat holes around pipe penetrations using scissors — do not leave ragged gaps, as these become thermal bridges that negate the insulation.
- 5
Insulate the hot-water pipes too
The pipes leaving the top of the tank lose significant heat over their length. Slide pre-split foam pipe lagging (available in 15 mm and 22 mm inner diameters to match standard Greek copper pipework) along every accessible hot pipe run for at least one metre from the tank. Secure with tape at joints. Pipe insulation is especially valuable in outdoor cupboards or unheated basements where ambient temperatures drop in winter. Switch the heater back on, let it reach temperature, and feel the jacket surface — it should be barely warm, not hot.
Rather have a pro handle it?
Get a vetted plumbing pro in your city — one number, booked in EN/EL/DE.
FAQ
- Will insulating my tank void the manufacturer warranty?
- For most electric immersion tanks a blanket jacket does not void the warranty, but check your documentation first. Never cover the thermostat housing, the pressure-relief valve, or any rating labels. If your tank is still under warranty and you are unsure, ask the manufacturer or a licensed plumber before wrapping.
- Can I insulate a gas boiler tank myself in Greece?
- Gas appliances in Greece must be serviced by a licensed technician (αδειούχος τεχνικός φυσικού αερίου). While fitting a jacket around the water-storage cylinder of a combi system is sometimes straightforward, you should have a professional confirm that the jacket will not obstruct flue ventilation or safety controls before you proceed.
- How long does a tank jacket last and when should I replace it?
- A good-quality fibreglass or mineral-wool jacket lasts 10–15 years under normal conditions. Inspect it annually for signs of compression (flattened fill loses its insulating value), water damage, or tears in the outer skin. If the jacket feels damp or smells musty, replace it immediately — wet insulation conducts heat rather than blocking it.