Water Vapor Fireplace Buying Guide: How Mist Fireplaces Work, Plumbing, Maintenance and Best Models

A water vapor fireplace makes "fire" out of a fine mist and colored light. No gas line, no chimney, no combustion, nothing hot to touch. That is why it has become the go-to answer for New York City apartments, co-ops, restaurants and anyone who wants a long linear flame in a wall that could never take a vent. We have had water vapor fireplaces running on our Maspeth showroom floor for years. This guide is what we tell customers across the counter: how the technology works, what water and plumbing really involve, what maintenance looks like, and which Dimplex Optimyst, NetZero Waterplace and Aquafire models we would put in your home. Still deciding between vapor and a conventional LED unit? Read our water vapor vs. electric fireplace comparison first.

How does a water vapor fireplace actually work?

Under the media bed sits a shallow water sump. In it is an ultrasonic transducer, a small ceramic disc that vibrates fast enough to shake the water surface into a cloud of micro droplets. A quiet fan pushes that cloud up through a slot in the log set or media plate, and LEDs (amber on most units, full RGB on the newer ones) shine up through the rising mist. Because the mist tumbles and thins as it rises, the lit column flickers exactly the way flame does. Dimplex calls it Optimyst and holds the original patents; NetZero calls the same style of unit a Waterplace and refers to the transducers as "mist makers."

Three things follow. The flame is cool to the touch. There is no exhaust, so nothing to vent. And the effect depends entirely on the water: its mineral content, how clean the sump is, and how still the air in front of it is. Most of this guide is about those three things.

For a New York City buyer, the code side is simple. Electric fireplaces, vapor units included, need no Fuel Gas Code sign-off and no chimney. That matters here: vent-free gas appliances cannot be installed in New York City under the NYC Fuel Gas Code, and no new wood-burning fireplaces have been permitted since Local Law 38 of 2015. Co-op and condo boards still want to see your plan, but an electric appliance with no gas and no vent is about the easiest approval there is.

Should you use distilled or tap water?

Most people assume distilled water is the safe choice, the way it is for a steam iron. For vapor fireplaces that is wrong, or at least incomplete. The transducer needs some dissolved minerals in the water to throw a good mist; pure water produces a weak, thin flame. The three brands differ, so here is what the manuals say:

• Dimplex Optimyst. Normal tap water if it is not hard; softened or filtered water if it is. If you run distilled, the cassette manual says to add 1/8 teaspoon of salt to restore conductivity. The Linear ships with an in-line mesh filter, and Dimplex advises against unfiltered well water.
• NetZero Waterplace. No distilled or reverse osmosis water. NetZero specifies soft or slightly hard water, 3.5 to 8.5 grains per gallon, and offers an inline filter kit for plumbed installs.
• Aquafire. Same 3.5 to 8.5 grain window, 7.0 ideal, no reverse osmosis. Aquafire sells a Vapor Pure softener with replacement cartridges, and says untreated hard water is the most common reason a warranty claim is denied.

Why the fuss about hardness? Every ounce of water that leaves the sump as mist leaves its minerals behind on the transducer. Hard water scales a transducer in weeks and the flame gets short and patchy. New York City tap water is soft: the DEP's 2025 quality report puts it at 1 to 6 grains per gallon, averaging 2, which is below the 3.5 grain floor NetZero and Aquafire publish. In our experience it still throws a good flame straight from the tap, and scale is never the problem here. If a unit on city water runs a thin flame, ask us before adding anything to the water; Dimplex is the only one of the three whose manual allows the salt trick. Long Island, parts of New Jersey and most of South Florida draw from wells and aquifers that run harder, and that is where we spec a softener or filter kit from day one.

Does it need a water line or a drain?

Every unit we sell can run from an internal tank you fill by hand. The question is whether you want to.

Reservoir fill. NetZero's 20, 40 and 60 inch burners hold 2, 4 and 6 liters and run about 20 hours per fill; Aquafire's Pro inserts hold 2, 4 and 6.5 liters for a similar 20 hours. Dimplex's Pro 500 cassette uses a 42 ounce container rated for up to 12 hours, and the Linear's optional container lasts about 6 hours per flame module, which is why Dimplex calls hand-filling the Linear "not recommended for frequent use." The Dimplex Revive and Aura cabinets have a pull-out water drawer.

Plumbed. If the fireplace will run every evening, or it is a long multi-unit feature, plumb it. All three brands connect to a cold water line with 1/4 inch OD tubing, the same tubing that feeds a refrigerator ice maker. By brand:

• Dimplex cassettes and Linear use the CDFIPLUMB-KIT. Multiple cassettes get a manifold so every sump sees the same pressure.
• NetZero's standard NZW burners need the separate Direct Plumb Kit; without it the manual warns the unit will overfill and leak, and the enclosure height grows from 11 to 12 inches. The NZWP Platinum burners accept a 1/4 inch PEX line directly.
• Aquafire builds direct plumbing into the Pro insert; the standard and Lite inserts take the AWA direct plumb kit. Supply pressure is capped at 100 PSI.

Drains. None of these ties into a drain line. When you descale you drain into a bucket: NetZero's drain port into a 3 to 5 gallon pail, Aquafire's fill-and-drain tube, Dimplex by lifting out the sump. So leave access. A fireplace buried behind a fixed stone face with no access panel is a nightmare at cleaning time; we frame an access door below or beside the unit on our built-ins.

How much water does it use, and will the room get humid?

No manufacturer publishes a per-hour consumption figure, but they publish tank size and run time, so we can work it out. A NetZero 40 inch burner empties 4 liters over roughly 20 hours: about 0.2 liters, or 7 ounces, per hour. A 60 inch is about 0.3 liters an hour. Dimplex's 20 inch cassette works out to roughly 0.1 liters an hour. Call it 3 to 4 ounces of water per hour for every 20 inches of flame, more on the highest setting.

That water ends up in your room as vapor. In an ordinary living room with the HVAC cycling it is a small bump in relative humidity, and NetZero states there is no risk of moisture buildup on surrounding surfaces. Two cautions. In a small sealed room, a damp basement, or a space already at 60 percent humidity in a New York August, it adds up over a long evening. And the mist condenses on things right next to it: Dimplex says some condensation on the media plate is normal, and both Dimplex and NetZero warn that driftwood laid across the flame slot collects water. Keep media off the slot. None of these units are rated for outdoors, and Dimplex requires a GFCI circuit in bathrooms; the firebox makes mist, it is not built to receive it.

Does a water vapor fireplace give off heat?

The flame gives off nothing. Warmth depends on whether the maker bolted a heater to the unit:

A flame-only vapor unit draws about as much power as a few light bulbs, so it is the cheapest fireplace of any kind to leave on all evening. The Dimplex heaters are ordinary electric space heaters: about 1,500 watts on 120 volts is roughly 5,000 BTU, enough to take the chill off a 400 square foot room, not enough to heat a loft. If heat is a real requirement, we would usually steer you to a 240 volt electric or a direct vent gas unit and keep the vapor fireplace for looks.

What sizes and configurations are available?

Vapor hardware is modular: the flame is produced in a tray, and trays line up end to end.

• Dimplex sells Optimyst in 20 inch cassettes (the Pro 500 and the RGB Cassette), in 40 and 60 inch Pro Boxes (the Pro 1000, Pro 1500 and the RGB Pro Box 40 and Pro Box 60), and finished Linear fireboxes at 46, 66 and 86 inches. Cassettes join to any length, and up to five sync to one remote.
• NetZero burners come in 20, 40 and 60 inches, link as main and secondary units, and are rated for up to 20 feet of continuous flame.
• Aquafire inserts come in 20, 40 and 60 inches and gang to 20 feet on one remote. The modular steel Aquafire Box with 20 inch expansion panels saves framing a custom cavity.

Because nothing is hot and nothing vents, the firebox can be open on as many sides as you like. NetZero publishes single-sided, left corner, right corner, three-sided, see-through and peninsula firebox drawings for the same burner. The Dimplex Pro Box converts to see-through by removing the backer panel; the Optimyst Linear installs front-facing, left corner, right corner or bay; the e-MatriX is a two-sided box with a glass kit. A fully open installation with no glass at all is possible and looks spectacular, with one condition we cover next: still air. One more option worth knowing: Amantii's "Optimyst-ready" Signature TRD 38 is a finished traditional-style firebox that accepts the Dimplex cassette, no custom framing needed.

What does the enclosure need for airflow?

The cavity must breathe from below. The fan that lifts the mist pulls room air in through the bottom and sides of the unit. Dimplex requires 40 square inches of air inlet for a 20 inch cassette and 80 for a 40 inch; the Optimyst Linear needs 80, 120 and 160 square inches for the 46, 66 and 86. NetZero and Aquafire both specify 50 square inches of intake per 20 inches of unit length if media covers the top vents. That air can come through a toe-kick grille, a front register or side registers; it cannot come from an open stud bay. NetZero's manual is blunt: the enclosure must be sealed and open only to the room, or negative pressure flattens the flame and can damage the unit.

The flame needs headroom. Dimplex asks for 18 inches of clear space above a cassette (16 minimum) so the mist can rise and dissipate; NetZero asks for 2 inches around the device.

Still air, always. Mist is light. A supply register blowing across the opening, a ceiling fan overhead, or a door to a windy terrace will push the flame sideways or out entirely. NetZero says not to use the unit in a room with air currents; Aquafire warns that HVAC currents aimed at the insert stop the vertical rise. The fixes are easy if planned: glass on the viewing side (Dimplex recommends a 10 inch glass or acrylic barrier where there is air movement), an Aquafire ClearShield wind screen, or redirecting the nearest register.

Light trap. The LEDs under the flame glare when seen from above. Mount the unit so a seated viewer looks across the flame, not down into it: Dimplex puts the bottom of the Linear 5 to 50 inches off the floor, and Aquafire specifies a 19 inch minimum hearth setback.

How loud is it, and what flame colors can you get?

Sound. A vapor fireplace is not silent. There is a low fan hum that Dimplex's manual describes as audible in very quiet rooms and normal. Dimplex adds an optional wood-fire crackle with six volume levels. NetZero and Aquafire units beep to confirm flame changes and when the tank runs low. Expect roughly 45 seconds between powering on and the first mist appearing.

Light. The original Optimyst look is amber, still the most convincing wood-fire imitation. The color options have moved fast:

• Dimplex RGB Cassette, RGB Pro Box and Linear: eight themes (Natural Flame, Blue, Violet, Red, Aquamarine, Prism, Kaleidoscope, custom via the Flame Connect app) and six brightness levels including a slow pulse.
• NetZero Platinum (NZWP): a switchable orange row plus an RGB row with 15-color smooth and fade cycles. Standard NZW burners are orange only.
• Aquafire Pro: dual amber and RGB light bars, 30-plus presets, adjustable density, speed, brightness and fade. The standard insert is natural orange.

Our honest take: buy the RGB versions for the dimmable, app-controlled amber as much as for the party colors. A soft low amber is what people actually use most.

What maintenance does it need?

This is the part brochures skip. A vapor fireplace has a wet sump and needs the same attention a good humidifier does. Straight from the current manuals:

Rules that save transducers: never scrub a mist maker with a stiff brush or scouring pad, never put the plastic parts in a dishwasher, and cut power at the panel before opening the sump. Budget roughly an hour a month. If that is more than you will do, buy a plumbed unit with a softener and the chores shrink to a quarterly vinegar soak.

Can it be used in a restaurant or lobby?

A lot of the vapor fireplaces we quote are for restaurants, hotel lobbies and spas: nothing hot for a guest to touch, no combustion air to manage, and a 20 foot flame line across a bar back that gas cannot match without a serious vent chase. Dimplex rates the Pro line for residential or commercial installation; Aquafire's Pro carries a 1 year commercial warranty versus 2 residential. On a commercial job we always plumb the unit, add the filter or softener, wire a dry-contact wall switch so staff never hunt for the remote, and set up quarterly descaling. A vapor feature nobody cleans looks tired within a season.

Our recommended models

We picked these from the units we install and service most, weighted toward what still looks good after a year of use. Dimplex is the choice when you want heat or a finished box; NetZero and Aquafire are the choice for long runs, open fireboxes and plumbed installs. (Modern Flames has shown a steam unit called FusionFire; we do not stock it, so it is not on this list.)

Dimplex Optimyst

Best OverallDimplexOptimyst Linear OLF66, 66 inThe only vapor unit we carry with a thermostat heater, 120 or 240 V, and corner or bay configurations out of the box.View details →Best for HeatDimplexOptimyst Pro 1000 Built-In, 46 inA finished steel box with a hardwired 4,981 BTU heater that converts to see-through by pulling the backer panel.View details →Best for Custom BuildsDimplexOptimyst Pro 500 Cassette, 20 inThe 20 inch building block: chain cassettes to any length at 230 W each, no heat, your millwork around it.View details →Best for Color ControlDimplexOptimyst RGB Cassette, 20 inThe same cassette with eight flame themes, dimmable amber and app control, which is what people actually use.View details →

The Pro 1500 and RGB Pro Boxes, the 46 and 86 inch Linears, and the plug-in Aura and Mapleton stove round out the Dimplex line; all are linked in the sizes section above.

NetZero, Aquafire and plug-and-play

Best ValueNetZeroWaterplace NZW40B, 40 inThe burner on our showroom floor: 4 liter tank, about 20 hours per fill, and six firebox configurations from one unit.View details →Best for Long RunsNetZeroWaterplace Platinum NZWP60B, 60 inDirect plumb without a kit, an RGB row and a Wi-Fi app, and it links to 20 feet of continuous flame.View details →Best for CommercialAquafirePro Series Insert, 20 / 40 / 60 inBuilt-in direct plumbing, UV-C sanitizing and 30 plus colors make it the easiest unit to keep clean in a lobby or bar.View details →Best for Small SpacesDimplexOptimyst Revive, 25 inPlug-in, built-in heater and a pull-out water drawer, so a rental or co-op gets a vapor flame with no framing.View details →

The full NetZero line includes fireboxes and kits. On the Aquafire side, the standard and Lite inserts trim features for tighter budgets, and the Gatsby is a 16 inch freestanding piece for a console.

All water vapor fireplacesDimplex OptimystNetZero WaterplaceNetZero fireboxes and kitsAll electric fireplaces

Which should you choose?

For most homeowners asking us for a 20 to 40 inch feature, we specify a Dimplex Optimyst cassette or Pro Box, plumbed if it will run nightly, with a softener outside the five boroughs. For a long feature wall, a see-through or an open hearth, we specify NetZero, usually Platinum. For restaurants and lobbies we lean Aquafire Pro for the UV-C and the direct plumbing. Whatever you pick, decide the water line, the air inlet and the access panel before the framer shows up.

Frequently asked questions

Do water vapor fireplaces give off heat?

The flame does not. Some models add a conventional electric heater: Dimplex's Pro Box, Linear, Revive, Aura and Mapleton all include one (roughly 4,300 to 5,100 BTU at 120 volts, more on the 240 volt Linear). NetZero Waterplace and Aquafire units have no heater at all. Treat any vapor fireplace as decorative first and supplemental heat second.

Will a water vapor fireplace make my room humid or cause mold?

Working from the makers' tank and run-time figures, a 40 inch unit releases about 7 ounces of water an hour, a minor change in a normal room. Keep it out of tightly sealed damp spaces, keep media off the flame slot so condensation does not pool, and clean the sump monthly so nothing grows in the standing water.

Do I have to use distilled water?

No, and for NetZero and Aquafire you should not: both prohibit distilled and reverse osmosis water because the transducer needs dissolved minerals to make mist. Dimplex allows distilled with a pinch of salt. All three want soft to moderately hard water, about 3.5 to 8.5 grains per gallon. NYC tap water averages about 2 grains, softer than that window, and in our experience works straight from the tap. Harder well water on Long Island, in New Jersey and in Florida calls for a softener or filter kit.

How often do I have to refill the tank?

NetZero and Aquafire tanks run about 20 hours per fill. The Dimplex 20 inch cassette runs up to 12 hours on its 42 ounce container, and the Dimplex Linear about 6 hours per container, which is why Dimplex recommends plumbing the Linear. Connected to a 1/4 inch cold water line, any of them run indefinitely.

Can I install a water vapor fireplace in a New York City apartment or co-op?

Yes. It is an electric appliance with no gas, no venting and no combustion, so the NYC Fuel Gas Code restrictions on vent-free gas and the Local Law 38 limits on new wood-burning fireplaces do not apply. Built-ins still need an electrician, and a plumber if you want a water line, and your board will want to see the plan, but an appliance with no gas and no vent is an easy approval.

Are water vapor fireplaces loud?

There is a low fan hum, noticeable in a silent room and lost under normal conversation. Dimplex adds an optional crackle sound with six levels. NetZero and Aquafire beep to confirm settings and when the tank is empty. Expect about 45 seconds between switching on and the first visible mist.

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Written by the NYC Fireplaces & Outdoor Kitchens team. Last reviewed October 2026. We sell, install and service the products discussed here.

Sources:Dimplex Optimyst Linear installation and user guide, Dimplex Optimyst Cassette spec sheet and CDFI500-PRO / CDFI1000-PRO installation manual, Dimplex GBF1000-PRO sell sheet, Dimplex Optimyst brochure (2025), NetZero Waterplace burner instructions (85-03-01257, 2025), Aquafire Pro AWPR specifications and installation guide (2026), Pro Builder on Modern Flames FusionFire, 2022 New York City Fuel Gas Code, NYC Local Law 38 of 2015, NYC DEP 2025 Drinking Water Supply and Quality Report. Specifications change; always confirm with the manufacturer's current installation manual.