“Guaranteed savings” is one of the easiest phrases in the trade to print and one of the hardest to enforce. A guarantee with no baseline, no measurement period and no stated remedy is a slogan. A guarantee with all three is a financial commitment, and the company making it has to be confident in its own arithmetic.
We offer one on our Certified line, so we have had to work out exactly how it is checked. What follows is how we do it, why we chose this method over the alternatives, and where the method has limits. Whether you buy from us or from anyone else, these are the questions to ask before you trust a percentage.
Step one: decide what is being guaranteed
The first trap is the number itself. Most advertising figures, ours included, are an upper bound: the best result the measures could plausibly produce on a villa with nothing shading the glass. That is a fair way to tell people what is possible. It is a poor thing to guarantee, because no individual villa is the average case.
So the figure in the contract is not the advertised one. It is the figure the surveyor issues after measuring your villa: every elevation, the actual glass, the roof build-up, the bill history. Our engine has two modes for exactly this reason. Marketing mode is the top of the honest range; survey mode is the conservative figure we are prepared to sign.
Here is the difference on our standard case: a 250 m² villa with double clear glass and a 1,150 AED monthly electricity bill, about 44,100 kWh and 13,966 AED a year. The package is solar control film, a cool roof coating, door and window seals, and smart thermostats.
| Survey mode (contract) | Marketing mode (upper bound) | |
|---|---|---|
| Electricity saved per year | 7,059 kWh | 8,845 kWh |
| Saved per year | 2,547 AED | 3,172 AED |
| Share of the bill | 18.2% | 22.7% |
Across five villa and townhouse sizes at three bill levels each, survey mode for this package came out between 13.2% and 20.5% of the electricity bill. Marketing mode was 15% to 29% higher than survey mode in every case. That gap is deliberate, and it is the reason the calculator on our home page is described as an estimate rather than a promise.
Why the signed figure is lower than the physics
A calculation is always more optimistic than a meter. Blinds were already shading part of the glass. Some rooms are rarely cooled. The air conditioner does not run at its rated efficiency. Our engine handles this in two ways before any number reaches a contract.
- A 75% realisation rate. In survey mode, the calculated saving is multiplied by 0.75. Measurement and verification practice for envelope retrofits puts the ratio of metered to calculated savings at roughly 0.7 to 0.8, and we sit in the middle of that band.
- A ceiling on the envelope. Film and roof together are never allowed to claim more than 40% of the air conditioning load, however large the glass area. This stops a big villa with a lot of west-facing glass producing a figure no meter would ever show.
The point of both is simple: if the company carries the risk of a shortfall, it has every reason to be conservative. If a guarantee is offered on a number that looks generous, ask who pays when the meter disagrees.
Step two: fix the baseline
Every savings claim is a comparison, and the comparison is only as good as the “before”. We use twelve months of DEWA history before the work. A full year matters in Dubai because cooling dominates the bill and the summer months behave nothing like the winter ones. On our standard villa, the July bill is more than two and a half times the January one. A three-month baseline taken in spring would make almost any measure look either brilliant or useless, depending on which way you compared it.
The baseline has to be real readings. If any of those twelve bills were estimated rather than read, the comparison is distorted from the start. Our article on why a DEWA bill suddenly jumps explains how to spot an estimated reading, and it is worth checking before anyone, us included, uses your history as a yardstick.
Step three: measure the same twelve months after
After the work, we take the twelve months that follow and compare them with the same twelve months before. Month for month, so that an August is compared with an August. This is a whole-house meter comparison, the approach the international measurement protocol (IPMVP) calls Option C. It has one great strength: it uses the DEWA meter, which neither side controls, rather than a sensor we install and read ourselves.
Adjusting for tariff changes
DEWA charges by slab, and the fuel surcharge on top of every kilowatt-hour is reviewed regularly. If the tariff moves between the two years, comparing dirhams with dirhams would hide or invent a saving that has nothing to do with the house. So both years are priced on the same tariff before the comparison is made. The question being answered is how much less electricity the villa used, valued fairly, not what DEWA decided to charge.
The valuation itself follows the bill. A kilowatt-hour you avoid comes off the top slab you reach that month, so a summer saving is worth more per unit than a winter one. On our standard villa the survey-mode saving works out at about 0.36 AED per kWh across the year, with the largest single month, July, worth about 376 AED.
Step four: agree what does not count
A whole-house comparison is fair only if the house is the same house. Some changes add load that no envelope measure could offset, so they are excluded in writing before the work starts:
- More people living in the villa than during the baseline year.
- An extension or a converted space that is now cooled.
- A new swimming pool, with its pump running every day.
- An electric car charger.
Each of those is something the owner decides, and each can add more consumption than the retrofit removes. Listing them up front is what keeps the guarantee from turning into an argument a year later.
Promises you cannot verify
Some savings claims are impossible to check on a meter, and an honest contractor will tell you which ones. Two from our own range:
- Clear facade impregnation. It does not change the colour of the wall, so it does not change how much sun the wall absorbs. On our standard villa, our engine puts its energy effect at about 4 AED a year. We sell facade protection for what it does: keeping water and dirt out of the render.
- Pool deck coating. It makes the surface 15 to 25 °C cooler under bare feet. That is comfort, checked with your feet, not with a meter, so we never attach a bill saving to it.
If anyone offers to guarantee a bill saving from either of these, ask how they intend to measure it.
When a guarantee is not worth paying for
A guarantee costs something, because the materials behind it have to be independently tested and the company carries the risk of a shortfall. That is why our Essential line, with direct-import materials, carries no savings guarantee, and we say so before you sign. If you plan to sell within a couple of years, you will not be the one holding the bill twelve months later, and the cheaper line usually makes more sense. If you plan to stay, the guarantee is the part of the price that turns an estimate into a commitment.
Questions to ask any contractor
- Is the guaranteed figure the advertised one, or one calculated for my villa after a survey?
- What is the baseline period, and does it cover a full summer?
- Is the comparison made on the DEWA meter or on your own sensors?
- How are tariff changes handled between the two years?
- What happens, in dirhams, if the result is short?
- Which changes on my side void the comparison, and are they listed in the contract?
Our own answers are summarised on the pricing page, next to every rate we charge. To see which measures carry most of that 18% on a typical villa, and why film and thermostats each do more than the roof coating on every size we model, read how to reduce a high DEWA bill.