Insulating a hot water system: the tank cover, the pipes, and where it must not go
A jacket on the tank sounds like an easy win. Sometimes it is. On many modern systems it is pointless, and on some it is a hazard.
A hot water tank cover, or insulation blanket, is a jacket that wraps around a storage cylinder to slow the heat escaping through its walls. Whether it helps depends on how well your tank is already insulated. For most systems made in recent years, the answer is: not much, and not at all on some.
The first thing to do is look at the data plate and the manual. If the manufacturer says no add-on covers, that settles it.
Is a tank cover worth fitting?
Tanks lose heat all day, because the water inside is kept hot whether you use it or not. This is called standing loss. An old, poorly insulated cylinder can lose a fair amount. A modern one with factory insulation loses far less, so a blanket adds little.
If you have an older unit that feels warm to the touch on its outer jacket, a cover might make a noticeable difference. If the outside of the tank is cool, the factory insulation is doing its job and a blanket will not improve it.
Be honest about the age of the system as well. A cover on a tank that is near the end of its expected service life is money spent on something you are about to throw out.
Where must insulation never go?
This is the part that matters for safety. A cover wrapped carelessly can block things that need air or access.
| Area | Why it must stay clear |
|---|---|
| The relief valve and its drain pipe | It must be able to open and discharge freely. See the temperature and pressure relief valve |
| The electrical cover and controls | Needs access and clearance. Covering it can trap heat around live equipment |
| Vents, flues and air intakes | Gas and heat pump units need airflow. Blocking it is dangerous |
| The data plate | You and a plumber need to read the model and rating |
Gas units are a hard no for add-on wraps. The flue and the air supply are safety-critical, and the manufacturer almost always prohibits anything around the unit.
What about insulating the pipes?
This is usually the better buy. Every metre of exposed hot pipe between the tank and the tap loses heat, and it makes you run the tap longer waiting for hot water to arrive. Foam pipe lagging is cheap, and it is a sensible thing for a householder to fit on exposed straight runs of pipe, particularly outdoors.
Insulate the first stretch of pipe leaving the tank, and any long exposed run. Do not wrap the relief valve pipe, and keep lagging back from any fitting you may need to reach. If your hot water is slow to arrive at a distant bathroom, this is also worth reading alongside the four kinds of hot water saver.
A position worth taking
If your system is modern, skip the tank blanket and lag the pipes. If it is old and warm to the touch, a cover from the manufacturer or a reputable supplier may pay off. But you may be better off planning the replacement.
What is genuinely yours to do
- Read the manual first. If it prohibits covers, do not fit one.
- Feel the outside of the tank. Warm to the touch means it is losing heat. Cool means the insulation is fine.
- Lag exposed pipes near the tank and along any long outdoor run, keeping clear of the relief valve and fittings.
- Check your warranty. An unapproved cover can cause a dispute, so see what actually voids a hot water warranty.
- Ask your plumber at the next service whether a cover would help your particular unit.
Frequently asked questions
Does a hot water tank cover save energy?
It can on an older, poorly insulated tank, where standing loss through the walls is significant. On a modern system with good factory insulation the gain is small. Feel the outside of the tank: if it is warm, heat is escaping, and if it is cool, a cover adds very little.
Can I put a blanket on any hot water system?
No. Many manufacturers prohibit add-on covers, and gas and heat pump units need clear airflow, flues and vents. Always read the manual first and never cover the relief valve, its pipe, the electrical cover or any vent.
Is it better to insulate the pipes or the tank?
For most modern systems, pipe lagging is the better buy. Exposed hot pipes lose heat along their whole length and make you wait longer for hot water. Foam lagging on exposed straight runs is cheap and suitable for a householder to fit, keeping clear of valves and fittings.
Will a tank cover void my warranty?
It can, if the manufacturer prohibits add-ons or the cover blocks required clearances. Check the manual and the warranty terms before fitting anything, and ask the manufacturer if they are unclear.
Should I insulate a gas hot water system?
Do not wrap a gas unit. The flue and air supply are safety-critical, and manufacturers almost always forbid add-on covers. Any work on the gas side is for a licensed gasfitter.
Sources
What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.
- Australian Government, energy.gov.au. Hot water systems — types, installation and energy performance
- Australian Building Codes Board. National Construction Code — Volume Three (Plumbing Code of Australia)