Ambient Fragrance Formulation for HVAC Systems: Carrier Selection & Viscosity Control

A skin perfume and a scent that permeates an entire hotel do not follow the same rules. One involves a few grams of liquid in contact with your skin; the other is an engineering problem governing cubic metres of air. HVAC scent systems (fragrance diffusion connected to a building's ventilation ductwork) and nebulisation (technology that breaks a fragrance oil into micron-scale droplets using pressurised, alcohol-free air) demand an entirely different formulation logic.

Here you are writing a formula for a device and for air, not for skin. The fluidity of the fragrance oil, its evaporation rate, and whether its carrier will clog the device nozzle — every one of these factors must be accounted for individually. Pouring a skin-ready perfume concentrate straight into an HVAC unit as-is is a path that usually ends in blocked nozzles and disappointment.

In HVAC and nebulisation formulas, alcohol is generally unwanted. High-grade ethanol is flammable (low flash point) and creates problems inside enclosed duct systems in terms of both safety and fragrance purity. In its place, alcohol-free carriers take centre stage.

There are two main players: DPG (dipropylene glycol) and IPM (isopropyl myristate). Neither is a fixative; they are carrier solvents and emollients — they dilute the fragrance oil, adjust its fluidity, and moderate volatility to some degree. Labelling them "longevity additives" is inaccurate; they simply establish the solvent environment.

In practice the two are used together: DPG builds the body of the formula and IPM thins out the flow. For sourcing pure DPG, refer to the esans.com.tr DPG page to get started on your own blend ratios.

Viscosity is a liquid's resistance to flow. A formula that is too thick will block nozzles and fail to form droplets; one that is too thin will flow uncontrolled and be over-consumed. The goal is to hit the flow-rate window that your device requires.

Heavy resins, balsams, and certain synthetics (density >1.10) thicken the formula. Light volatile materials such as citrus (~0.84) thin it. The density difference is critical: if you think only in grams and overlook the corresponding millilitre volume, you will encounter overflow or under-fill during volumetric filling. Always factor density into every ml↔g conversion.

Example: the millilitre equivalent of a 100 g formula could be anywhere from 88 ml to 102 ml depending on the proportion of heavy materials it contains. Building your filling line around weight (grams) is the safe approach; calculate the ml label figure afterwards using density.

Vapour pressure determines diffusion power. High volatility = a strong initial burst but a short duration. Longevity and concentration are not the same thing: keeping an ambient scent constant throughout the day is achieved not by increasing the proportion but by balancing the volatility profile of the formula. A high-concentration citrus-dominant formula will dissipate rapidly in the air, whereas a lower-concentration amber–musk-bodied formula will hold in the ductwork for hours. Never promise absolute hours; test every formula in its own space.

Production discipline determines the consistency of the result. The sequence below scales from small batch to full production run without deviation.

1. Prepare the carrier

   Weigh DPG and IPM to your target ratio and combine them on a magnetic stirrer. Work by weight (grams); note the density difference.

2. Add the fragrance oil

   Slowly incorporate the fragrance oil into the carrier while homogenising. If heavy resins are present, apply gentle heated stirring, then return to room temperature.

3. Maceration (room temperature)

   Allow the blend to rest at ~15–20 °C in the dark. Maceration is chemical maturation; it slows as temperature drops, so do NOT refrigerate. A dark environment protects the fragrance from light degradation.

4. Chilling

   Once maturation is complete, chill the blend at ~0–4 °C for approximately 24 hours. This causes any insoluble waxy structures to precipitate. This step is SEPARATE from maceration and comes after it.

5. Cold filtration

   Pass the chilled blend through a fine filter. If this step is skipped, sediment will form in the nozzle and at the bottom of the bottle, gradually blocking the device.

6. Device test

   Trial the filtered formula in the actual device. Observe droplet size, flow rate, and scent intensity in the space; fine-tune viscosity with the IPM ratio if necessary.

Ambient fragrance blends into air that many people breathe in an enclosed space. The safety requirements are therefore no less stringent than for skin-applied products — in fact, they demand even greater care.

IFRA limits apply not to the overall fragrance oil concentration but to individual molecules within the formula and to the product category. A blanket statement such as "HVAC fragrance is safe up to X concentration" is incorrect. Always request and read the IFRA compliance certificate for the fragrance oil you are using.

Safety depends on the molecule, not the source. The perception that "natural = safe, synthetic = risky" is mistaken: the strictest IFRA restrictions (e.g. Citral, Eugenol, oakmoss) often apply precisely because these materials occur in high concentrations in natural essential oils. Conversely, certain pure synthetics can be almost entirely allergen-neutral. What matters is the molecule and the use level.

On the product notification side, the process (notification steps) and responsibility (obligations of the responsible person/manufacturer) are distinct matters. Company registration and product notification on the ÜTS system are subject to official fees; for current procedures and fee amounts, consult official TITCK (Turkish Medicines and Medical Devices Agency) sources.