Underfloor Trial



In 2013 Fujitsu New Zealand released the new Fujitsu Inverter hot water heat pump named Waterstage. The on board technology enables home owners to heat multiple loads using one inverter heat pump. It is capable of creating hot water to manage underfloor heating, hot water radiators, domestic hot water cylinders, swimming pools and spa pools.
At 4.35 COP the Fujitsu Waterstage Inverter heat pump is extremely efficient. AHC teamed up with Fujitsu New Zealand and put together a trial to see just how good this new product was.
Click here for the brochure regarding the Waterstage Range


We designed the trial to cover house heating – 176 square metres of hydronic under floor heating, domestic hot water heating with a 300 litre cylinder and to tick the lifestyle box a 2000 litre cedar hot tub. The objective was to load up the heat pump and put it through its paces. We wanted to see how efficient this system was. We decided it needed to be cold, we didn’t want to know how efficient the system was in mild 7 degree winter weather - this didn’t interest us. We wanted cold frosty mornings with bone chilling southerly’s, hail, rain and general all round miserable weather. Luckily we knew some people building a new home in Taranaki. It is the perfect location, surrounded by rugged west coast beaches with a giant snow covered mountain sitting right bang in the middle.

The System

The system chosen was the smallest of the Waterstage units at only 10kw. The system was installed during the build process and was completed ready for the 2014 winter. All power is run through individual KW hour meters to track usage. The 176 square metre underfloor heating was run on its own for 3 months to give us a standalone reading for house heating only. This was set to 19 degrees with no restrictions on the time clock. During this time the Domestic hot water was heated using a 3kw electric element which we also tracked for power usage. The cedar hot tub is heated using a 2kw electric element which is tracked.

After 3 months the domestic hot water cylinder was hooked up to the Waterstage heat pump system. The cedar hot tub will be hooked up once we have enough data on the domestic hot water.


The original underfloor heating used an average of 11kw per 24 hour period over the three months.
11kw x 31 days =341kw / 341kw x 26 cents/kw =$88.66 /month

The original 300 litre cylinder with 3kw electric element used an average of 14kw per 24 hour period over the 3 months.
14kw x 31 days = 434kw / 434kw x 15.6 cents/kw= $65.10

The 300 litre cylinder powered by the Waterstage inverter heat pump used an average of 9kw per 24 hour period over 26 days
9kw x 31 days = 279kw / 279kw x 15.6 cents /kw =$41.85 Saving $23.25 /month

To date the system has performed excellently. This trial will be ongoing and the data here will be up dated regularly.