Aerona 290: efficiency does not fall with size the way it looks
Grant's five R290 sizes are ranked one way by SCOP at 35 degrees and another way at 55. Which column applies, and what the seven-year guarantee depends on.
What this means
At a 35 degree flow temperature the Aerona 290 SCOP figures run 5.00, 5.08, 4.74, 4.74, and 4.56 across the 4 to 15.5 kilowatt sizes, so the 6.5 kilowatt leads. At 55 degrees they run 3.66, 3.62, 3.69, 3.74, and 3.33, and the 12 kilowatt leads. The design flow temperature decides which ranking is the relevant one.
Equipment and model context
Grant Aerona 290 air-to-water heat pumps
- Aerona 290 4 kilowatt
- Aerona 290 6.5 kilowatt
- Aerona 290 9 kilowatt
- Aerona 290 12 kilowatt
- Aerona 290 15.5 kilowatt
Grant UK's Aerona 290 R290 range as published for the United Kingdom and Ireland. Grant states that the outputs are rated at minus 5 degrees Celsius air and 55 degrees water, which is a separate condition from the two temperatures the SCOP figures are quoted at.
What this guide covers
- Two adjacent sizes both cover the calculated heat loss and the choice is being made on efficiency.
- A quotation quotes one SCOP figure without saying which flow temperature it belongs to.
- A guarantee period that depends on who does the installation.
What changes the answer
- Seasonal efficiency is published at two flow temperatures and the range order differs between them.
- Rated output and rated efficiency are quoted at different conditions on the same range page.
| Model | SCOP at 35 | SCOP at 55 |
|---|---|---|
| 4 kilowatt | 5.00 | 3.66 |
| 6.5 kilowatt | 5.08 | 3.62 |
| 9 kilowatt | 4.74 | 3.69 |
| 12 kilowatt | 4.74 | 3.74 |
| 15.5 kilowatt | 4.56 | 3.33 |
The two columns disagree about the range
Read the 35 degree column and the range looks like a smooth decline with size: 5.00 on the 4 kilowatt, 5.08 on the 6.5, then 4.74 twice, then 4.56. The obvious reading is that smaller is better and the 6.5 is the sweet spot.
Read the 55 degree column and that disappears. The figures are 3.66, 3.62, 3.69, 3.74, and 3.33, so the 12 kilowatt unit is the strongest and the 6.5 sits fourth of five. The only agreement between the columns is that the 15.5 kilowatt is last in both.
Between the 6.5 and the 12 kilowatt units the gap is 0.34 SCOP points in favour of the smaller one at 35 degrees, and 0.12 points in favour of the larger one at 55. Neither gap is large, which is the point: the range is close enough that the choice should be made on capacity and siting rather than on a figure that reverses when a design assumption changes.
The rating condition is not the SCOP condition
Grant states that each model's output is rated at minus 5 degrees Celsius air temperature and 55 degrees water flow temperature. That is a cold-day, hot-water condition chosen because it is close to a United Kingdom design point for a retrofit.
The SCOP figures are not measured there. They are seasonal figures for a low-temperature and a medium-temperature application, and neither is a minus 5 degree rating.
So a 9 kilowatt Aerona 290 is a unit that produces 9 kilowatts at minus 5 with 55 degree water, and separately achieves 4.74 or 3.69 across a season depending on the design. Treating the badge kilowatt figure as an all-conditions output is what leads to a system that meets the heat loss on paper and not in February.
What the seven-year guarantee is attached to
Grant offers a seven-year guarantee on the Aerona 290, and it publishes a condition alongside it: installation by a G1 installer, where G1 installers have completed Grant's heat pump training. The guarantee is also subject to terms and conditions in the ordinary way.
That puts the guarantee on the same footing as most United Kingdom manufacturer terms, where the headline number is reachable rather than automatic. What differs between brands is what the condition is, and here it is who fits the equipment rather than a registration window.
For a buyer comparing quotations, that turns an apparently equal product into an unequal one. Two quotations for the same Aerona 290 from installers on different sides of that line are not offering the same guarantee.
R290 across the whole range
Every Aerona 290 size uses R290 and is inverter driven, with a built-in PWM circulating pump, a DC twin rotary compressor, low and high pressure protection, discharge temperature protection, and a factory-fitted automatic air vent and 3 bar pressure relief valve.
The list matters because it is a list of things not being bought separately. A factory-fitted pressure relief valve and air vent are components an installer would otherwise add to the primary circuit, and a built-in modulating pump is the part that lets the unit hold its own flow rate.
On sound, the range is Quiet Mark accredited with sound pressure between 37.0 and 42.6 dB(A) at one metre depending on size, which is a 5.6 decibel spread across a range that spans nearly four times the output.
| The project | What the published figures say |
|---|---|
| Underfloor at 35 degrees, small house | The 6.5 kilowatt leads the range at 5.08 |
| Existing radiators at 55 degrees | The 12 kilowatt leads at 3.74, the 6.5 sits fourth |
| Either design, largest size | The 15.5 kilowatt is last in both columns |
| A boundary close to the unit | Sound pressure spans 37.0 to 42.6 dB(A) by size |
| Comparing two installer quotations | The seven-year guarantee needs a trained G1 installer |
| Checking the capacity claim | Outputs are rated at minus 5 degrees air with 55 degree water |
Grant publishes a capacity condition and two efficiency conditions, and none of the three is the same operating point. Quoting a single kilowatt figure and a single SCOP together describes no state the machine is ever in.
- Minus 5 air, 55 waterWhere the kilowatt rating on the model name is measured
- 35 degree seasonalThe low-temperature application SCOP
- 55 degree seasonalThe medium-temperature application SCOP
- One metre, free fieldWhere the sound pressure figure is taken
Questions people ask about this
Which Grant Aerona 290 is the most efficient?
At a 35 degree flow temperature the 6.5 kilowatt unit leads with a SCOP of 5.08. At 55 degrees the 12 kilowatt leads with 3.74 and the 6.5 drops to fourth of five. The design flow temperature settles which answer applies.
What does the 9 kilowatt in Aerona 290 9kW refer to?
Grant states the outputs are rated at minus 5 degrees Celsius air temperature with a 55 degree water flow temperature. It is a capacity at that condition, not an output the unit holds across the whole operating range.
What do I have to do to get the seven-year Grant guarantee?
Grant attaches it to installation by a G1 installer, meaning an installer who has completed its heat pump training, and it remains subject to the published terms and conditions. Two quotations for the same unit can carry different guarantees for that reason.
How quiet is the Aerona 290?
Grant publishes sound pressure between 37.0 and 42.6 dB(A) at one metre across the range, with the figure depending on model size, and the range carries Quiet Mark accreditation.
What comes fitted inside an Aerona 290?
Grant lists a built-in PWM circulating pump, a DC twin rotary compressor, low and high pressure protection controls, discharge temperature protection, and a factory-fitted automatic air vent and 3 bar pressure relief valve. Those are components a primary circuit would otherwise need added.
Evidence recordHow this page was checked
official manufacturer support article · checked 2026-09-07
Every technical claim above was written from primary documentation held in the HVAC Bench evidence record: Grant UK technical literature. Where a source limits a definition to certain models, test conditions, or product classes, that limit is repeated here rather than generalised.
- Documentation class
- official manufacturer support article
- Scope of the definition
- Grant Aerona 290 air-to-water heat pumps
- Last checked
- 2026-09-07