Adding Insulation to a Hot Water Tank
By Bruce Barbour - June 2020
|The original hot water system.
Note that I had added additional insulation to the pipe work some time ago, soon after the unit was installed.
|The first step was to cut the
polystyrene top hat. It is 150mm polystyrene as that
is what I had available from the house building.
Diameter was the diameter of the tank plus twice the
thickness of the insulation, allowing an additional
bulge for the section of tank that had the pipes
sticking out of it.
|Stuck the insulation on with a
combination of silicon sealant (used as a glue) and
clothe tape. Originally I was going to use R2.5 wall
insulation (as that is what I had) but that was not
flexible enough to shape around the tank so I split
the batts down the middle making them R1.25 batts.
|Wrapped silver foil around insulated
tank. Used an upper layer and a lower layer.
Attached the upper layer to top hat with long screws
with washers. Used further tape to hold in position.
Used four pieces of foil for ease of handling.
(Only used foil because that was what I had. It would not be worth buying a roll to do this. Could use other plastic sheeting.)
|Cut a round piece of foil and covered
the top, securing to the side of the top hat with
Note that I also cut a slit in the insulation and coverings so the Pressure Relief Valve (PRV) was not prevented from operating and could be accessed.
From the data on the Enphase
system it appears that the insulation will save
about one quarter to one third of a kilo Watt hour per
day. (I had hoped for a half kWh per day saving.) If I was
using normal grid electricity this would save about $32
per year. However as I have a photo-voltaic system my
electricity cost for at least some of the electricity used
for heating the water is less than grid electricity.
Consequently I estimate my cost saving as $16 per year.
My extra material costs were for some tape and a tube of
silicon sealant. This will be paid for in the first year.
If I had to buy all the materials - at a guess - this
would cost approx. $100. This would be paid for in about
six year. However if I costed my labour the equation would
be different. I spent at least 8 hours over 2 days doing
this. If I costed my labour at a very cheap $30 per hour
the total cost would be $340. It would pay for itself in
21 years - so not financially viable. Luckily my labour is
free - to me.
A real cheap and dirty way of getting some extra
insulation on the tank would be to use an old doona quilt.
Wrap over the top and around the tank. Tape. Water proof
with a large heavy duty plastic bag such as a bag that
would come off a single bed mattress. Tape in position. It
will probably only be partial tank insulation. Ensure PRV
is not interfered with. Not very pretty nor as good as
what I did but very quick and cheap.
Couple of issues to be aware of. If you were considering insulating your tank, do this at your own risk. The information on this page is provided for general interest as a description of what I did and some other musings, not a recommendation to do it. I don't know whether the insulation would impact on tank warranty. If I had to make a claim I would probably remove the insulation prior to making the claim. I also realised after installing the insulation that I had potentially made 5 star mouse accommodation (a lovely heated area). I will have to monitor this and adjust if it is actually an issue.