# The Best Quest Dehumidifiers for Grow Rooms and Commercial Spaces

> Quest builds the workhorses that keep flower rooms out of the mold zone. Here’s which model fits your space, your circuit and your plant count.

Canonical: https://www.enthusiastreview.com/best/best-quest-dehumidifier/
Last updated: 2026-11-05
Published: 2026-11-05
Category: Brands
Publisher: Enthusiast Review

Walk into almost any serious indoor grow and you’ll find a **Quest dehumidifier** hanging from the ceiling or humming in a corner. Quest is the commercial and agricultural brand of Therma-Stor, the Madison, Wisconsin, company that also makes Santa Fe home units and Phoenix restoration dryers. Its machines are built for one job home dehumidifiers struggle with: pulling hundreds of pints a day out of warm, wet air, day after day, without icing or quitting.

That makes Quest overkill for a damp basement and exactly right for a flower room, a greenhouse, an indoor pool hall or a warehouse. The lineup is also in transition: Quest has been redesigning models around newer, lower-impact refrigerant, so the Dual 225 has given way to a new Quest 225 and smaller models are being refreshed. Below we sort out which Quest to buy, how to size it, and what to know about voltage, hanging kits, manuals and support.

## Our top picks

- **Best overall:** Quest Dual 155 — [check price on Amazon](https://www.amazon.com/s?k=Quest%20Dual%20155%20Overhead%20Dehumidifier&tag=sktiger-20)
- **Best for 115-volt rooms:** Quest Dual 205 — [check price on Amazon](https://www.amazon.com/s?k=Quest%20Dual%20205%20Overhead%20Dehumidifier&tag=sktiger-20)
- **Best for large flower rooms:** Quest 225 — [check price on Amazon](https://www.amazon.com/s?k=Quest%20225%20High-Efficiency%20Dehumidifier%20208%2F230V&tag=sktiger-20)
- **Best for commercial grows:** Quest 335 — [check price on Amazon](https://www.amazon.com/s?k=Quest%20335%20High-Efficiency%20Dehumidifier&tag=sktiger-20)
- **Best for warehouses and big facilities:** Quest 506 — [check price on Amazon](https://www.amazon.com/s?k=Quest%20506%20High-Capacity%20Dehumidifier&tag=sktiger-20)

For most small and mid-size grow rooms, the **Quest Dual 155** is the one to buy: it runs on an ordinary 115-volt circuit, hangs overhead and handles roughly a 20-gallon-a-day watering load with room to spare.

## 1. Quest Dual 155 Overhead Dehumidifier — Best overall

[Check price on Amazon](https://www.amazon.com/s?k=Quest%20Dual%20155%20Overhead%20Dehumidifier&tag=sktiger-20)

**Pros**

- 155 pints a day at 80°F and 60% humidity
- Runs on a standard 115-volt circuit
- Designed to hang overhead and free up floor space
- Among the most efficient models in Quest’s range

**Cons**

- Needs a drain or condensate pump — no bucket
- Too much machine for a single grow tent

**Why we picked it:** The Dual 155 hits the sweet spot of the lineup. It has enough capacity for a typical small commercial flower room or a large hobby room, yet it plugs into the same kind of circuit as a window air conditioner, so you don’t need an electrician to run 230 volts.

**Performance:** Quest rates it at 155 pints a day at 80°F and 60% relative humidity on roughly 8 amps at 115 volts. Its spec sheet puts it near the top of Quest’s range for water removed per kilowatt-hour, which matters when a unit runs most of the day through a long flower cycle.

**Worth knowing:** Quest sells an optional hanging kit for its 5-Series overhead models; confirm the kit matches your exact model before ordering.

| Spec | Value |
| --- | --- |
| Capacity | 155 pints/day at 80°F/60% (Quest) |
| Power | 115 V, about 8 A (Quest) |
| Mounting | Floor or hung overhead |
| Drainage | Gravity drain or condensate pump |
| Best for | Small to mid-size grow rooms |

## 2. Quest Dual 205 Overhead Dehumidifier — Best for 115-volt rooms

[Check price on Amazon](https://www.amazon.com/s?k=Quest%20Dual%20205%20Overhead%20Dehumidifier&tag=sktiger-20)

**Pros**

- 205 pints a day without a 230-volt circuit
- Overhead mounting keeps aisles clear
- Handles a bigger plant count than the Dual 155
- Widely stocked by hydroponics dealers

**Cons**

- Draws about 13 amps, so it needs its own circuit
- Some retailers list it at 200 pints, which causes confusion

**Why we picked it:** If your room has outgrown a Dual 155 but your electrical panel stops at 115 volts, the Dual 205 is the most capacity you can get from Quest on a standard outlet. It’s the model many growers step up to when they add lights or plants.

**Performance:** Quest’s documentation rates it at 205 pints a day at 80°F and 60% humidity on about 13.2 amps at 115 volts; you’ll see some listings round that down to 200. Because that current is above what a shared 15-amp circuit should carry continuously, plan on a dedicated 20-amp circuit.

| Spec | Value |
| --- | --- |
| Capacity | 205 pints/day at 80°F/60% (Quest) |
| Power | 115 V, about 13 A (Quest) |
| Mounting | Floor or hung overhead |
| Drainage | Gravity drain or condensate pump |
| Best for | Mid-size flower rooms |

## 3. Quest 225 High-Efficiency Dehumidifier (208/230V) — Best for large flower rooms

[Check price on Amazon](https://www.amazon.com/s?k=Quest%20225%20High-Efficiency%20Dehumidifier%20208%2F230V&tag=sktiger-20)

**Pros**

- 225-pint class capacity
- Redesigned around lower-impact refrigerant
- Fewer amps per pint on a 230-volt circuit
- Free-standing or hung with an optional kit

**Cons**

- Requires a 208/230-volt circuit
- Older Dual 225 parts and manuals don’t all carry over

**Why we picked it:** The 225 is the long-running favorite for bigger rooms, and the redesign keeps that capacity while moving to newer refrigerant. On 230 volts it draws less current than the Dual 205 does on 115, which makes it easier to stack several units on one panel.

**Performance:** The outgoing Dual 225 was rated at 225 pints a day at 80°F and 60% humidity and about 143 pints at 75°F and 50% — a useful reminder of how much ratings fall as a room dries. The current Quest 225 keeps the same capacity class on a 208/230-volt supply. Quest listed a five-year warranty on the Dual 225; check the terms that ship with the new model.

**Worth knowing:** Searching for a “Quest Dual 225 manual”? The Dual 225 is discontinued, so make sure you download the manual that matches the model number on your unit’s data plate.

| Spec | Value |
| --- | --- |
| Capacity | 225-pint class at 80°F/60% |
| Power | 208/230 V |
| Mounting | Floor, or overhead with hanging kit |
| Drainage | Gravity drain or condensate pump |
| Best for | Large flower rooms, greenhouses |

## 4. Quest 335 High-Efficiency Dehumidifier — Best for commercial grows

[Check price on Amazon](https://www.amazon.com/s?k=Quest%20335%20High-Efficiency%20Dehumidifier&tag=sktiger-20)

**Pros**

- 335-pint class from a single cabinet
- Offered in 208/230-volt and 277-volt versions
- Replaces two or more smaller units
- Built for continuous commercial duty

**Cons**

- Needs commercial-style electrical service
- Heavy — plan the mounting before delivery

**Why we picked it:** Once a room needs more than about 250 pints a day, one big unit is usually simpler to drain, wire and service than a row of small ones. The 335 is Quest’s mid-size commercial answer for licensed grows, greenhouses and production spaces.

**Performance:** As the name suggests, it sits in the 335-pint-a-day class at Quest’s standard 80°F and 60% rating condition. Like the rest of the lineup, it drains continuously, so you’ll want a floor drain or a condensate pump sized for its output.

| Spec | Value |
| --- | --- |
| Capacity | 335-pint class at 80°F/60% |
| Power | 208/230 V or 277 V versions |
| Type | Commercial compressor |
| Drainage | Continuous drain |
| Best for | Commercial grow rooms |

## 5. Quest 506 High-Capacity Dehumidifier — Best for warehouses and big facilities

[Check price on Amazon](https://www.amazon.com/s?k=Quest%20506%20High-Capacity%20Dehumidifier&tag=sktiger-20)

**Pros**

- About 500 pints a day from one machine
- Quest’s most efficient model by its published ratings
- 208/230-volt and 277-volt versions
- Works across a wide 56°F–95°F range

**Cons**

- Strictly a commercial install
- Original and current versions carry different ratings

**Why we picked it:** The 506 is the biggest name in the lineup and the one to choose when the space is measured in thousands of square feet: large flower rooms, warehouse grows, indoor pools and production floors where moisture never lets up.

**Performance:** The original 506 was rated at 506 pints a day at 80°F and 60% humidity; the current version is rated at about 500 pints with better efficiency, and Quest positions it as more efficient per pint than the 335. Its listed operating range runs from 56°F to 95°F, which covers almost any conditioned commercial space.

**Worth knowing:** If you see a 506 listed far below other dealers, check which version it is — older stock and open-box units are common.

| Spec | Value |
| --- | --- |
| Capacity | About 500 pints/day at 80°F/60% (current) |
| Power | 208/230 V or 277 V versions |
| Operating range | 56°F–95°F (Quest) |
| Drainage | Continuous drain |
| Best for | Warehouse grows, large facilities |

## Quest dehumidifiers, by the numbers

- **80°F / 60%** — Test conditions behind Quest’s pint ratings
- **155–500** — Pints per day across the current lineup
- **115 V vs. 230 V** — The circuit that decides your shortlist

That first number matters more than it looks. Home dehumidifiers are rated under the DOE’s 2019 test at a cool 65°F, which produces modest figures. Quest rates its machines at 80°F and 60% humidity — warm and wet, close to a flower room after lights-off — which yields bigger numbers. They’re honest numbers for that environment, but don’t compare them pint-for-pint with a portable from a big-box store, and expect less water once the room is already down near 50%. Our [dehumidifier size guide](https://www.enthusiastreview.com/guides/dehumidifier-size-guide/) explains the different rating systems.

## How we pick Quest dehumidifiers

We don’t run a grow room or a test lab. We compared Quest’s published spec sheets and manuals — rated capacity, amperage, voltage, operating range and mounting options — and checked which models are current, redesigned or being phased out. Then we read owner and dealer feedback from growers for recurring themes: drain problems, noise, reliability across long flower cycles and how well each size matches real plant counts.

The Dual 155 tops the list because it delivers commercial capacity without 230-volt wiring; bigger units earn their spots where one machine replaces several.

## What to look for in a Quest dehumidifier

- **Your electrical service:** The Dual 155 and Dual 205 run on 115 volts; the 225, 335 and 506 need 208/230 volts, and the larger two also come in 277-volt versions. Check your panel before you fall for a model.
- **Capacity with headroom:** Size to your watering, not your square footage, and add 20–30% so the unit isn’t running flat-out at the end of flower. See the sizing table below.
- **Overhead or floor:** Overhead models free up floor space and pull from the warm, humid air near the ceiling. Budget for the hanging kit and a ceiling that can carry the weight.
- **A drain plan:** Quest units have no bucket. Run a hose to a floor drain with a proper trap, or add a condensate pump if the unit sits below the drain.
- **Efficiency over a full season:** Compare pints per kilowatt-hour, not just pints per day. A unit running 18 hours a day for months adds up fast; our [electricity cost guide](https://www.enthusiastreview.com/guides/how-much-electricity-does-a-dehumidifier-use/) shows how to estimate it.
- **Control:** Decide whether you’ll use the built-in humidity setpoint or an external grow-room controller, and keep a separate hygrometer at canopy height to check the readings.

## What size Quest dehumidifier do you need?

In a grow room, plants are the humidifier. Nearly all the water you give them ends up in the air, so the simplest sizing rule is to convert your daily watering into pints: one gallon is eight pints. Then add headroom for the humid hours after lights-off.

| Water fed per day | Approx. moisture load | Quest that fits |
| --- | --- | --- |
| 10 gallons | About 80 pints | Dual 155 (plenty of headroom) |
| 15–18 gallons | 120–145 pints | Dual 155 |
| 20–22 gallons | 160–175 pints | Dual 205 |
| 25–28 gallons | 200–225 pints | Quest 225, or two Dual 155s |
| 35–40 gallons | 280–320 pints | Quest 335 |
| 50+ gallons | 400+ pints | Quest 506, or multiple units |

*A rule-of-thumb guide; rooms that run hot, use open reservoirs or flood tables need more capacity.*

> **One big unit or two smaller ones?:** Two Dual 155s cost more up front than one Quest 225, but they give you redundancy: if one fails mid-flower, the other keeps the room out of the danger zone while you fix it. For a single tent, skip Quest entirely and see our [grow tent dehumidifier](https://www.enthusiastreview.com/best/best-dehumidifier-for-grow-tent/) picks.

## Quest vs. Santa Fe, Phoenix and home dehumidifiers

Because Therma-Stor owns all three, the brands divide the work neatly. **Santa Fe** makes ducted and stand-alone units for basements, crawl spaces and whole homes — compare them in our [Santa Fe dehumidifier](https://www.enthusiastreview.com/best/best-santa-fe-dehumidifier/) guide. **Phoenix** builds portable LGR dryers for water-damage restoration, covered in our [Phoenix dehumidifier](https://www.enthusiastreview.com/best/best-phoenix-dehumidifier/) roundup. **Quest** handles agriculture and commercial spaces where the moisture load is constant.

- **Choose Quest** for grow rooms, [greenhouses](https://www.enthusiastreview.com/best/best-dehumidifier-for-greenhouse/), indoor pools and production spaces that need 150+ pints a day, every day.
- **Choose a whole-house unit** if the goal is a comfortable home; see our [whole-house dehumidifier](https://www.enthusiastreview.com/best/best-whole-house-dehumidifier/) picks.
- **Choose an LGR or rental** for a short-term flood cleanup; our [commercial dehumidifier](https://www.enthusiastreview.com/best/best-commercial-dehumidifier/) guide covers job-site units.

## Quest manuals, hanging brackets and customer service

### Finding a Quest manual

Quest posts installation and operation manuals on each model’s product page. The 5-Series manual covers the 105, 155, 165, 205 and 225 family, but the redesigned models have their own documents, so match the model and part number printed on your unit’s data plate before you follow wiring or drain instructions.

### Hanging kits and brackets

Overhead installs use Quest’s optional hanging kit. Anchor into structure, not drywall, and leave clearance for filter changes.

### Service and maintenance

- Check the air filter monthly in a grow room — plant debris and dust clog it quickly. Our [replacement filter guide](https://www.enthusiastreview.com/guides/dehumidifier-replacement-filter/) explains why that matters.
- Flush the drain line and trap between grows to prevent algae and slime clogs.
- Clean coils gently once a year; see our [dehumidifier maintenance](https://www.enthusiastreview.com/guides/dehumidifier-maintenance/) checklist.
- For warranty or repair questions, start with the authorized dealer you bought from, then Quest’s support team. Keep your receipt and serial number handy.

## The bottom line

For most grow rooms, the **Quest Dual 155** is the smartest buy: commercial capacity on a standard 115-volt circuit, with overhead mounting that keeps the floor clear. Step up to the **Quest Dual 205** if you need more water removal without rewiring, the **Quest 225** once you have 230 volts and a bigger room, and the **Quest 335** or **Quest 506** for commercial and warehouse-scale spaces. Size to your daily watering, leave headroom, and plan the drain before the unit arrives.

## Frequently asked questions

### Is a Quest dehumidifier worth it?

For grow rooms, greenhouses and commercial spaces with a constant moisture load, yes. Quest units are built to run long hours at high humidity and are far more efficient per pint than stacking home dehumidifiers. For a basement or a single grow tent, a residential unit is the better value.

### What size Quest dehumidifier do I need?

Convert your daily watering to pints (1 gallon = 8 pints) and add 20–30% headroom. Around 15–18 gallons a day suits a Dual 155, 20–22 gallons a Dual 205, about 25 gallons a Quest 225, and larger rooms a Quest 335 or 506.

### What’s the difference between the Quest Dual 225 and the new Quest 225?

The Dual 225 has been discontinued and replaced by a redesigned Quest 225 that uses newer, lower-impact refrigerant. Both are 225-pint-class units on 208/230-volt power. Use the manual that matches the model and part number on your unit.

### Does the Quest Dual 155 run on a regular outlet?

Yes. Quest rates it at about 8 amps on 115 volts, so it runs from a standard circuit. The Dual 205 is also 115-volt but draws about 13 amps, so give it a dedicated 20-amp circuit.

### Does the Quest 506 need 230 volts?

Yes. The Quest 506 comes in 208/230-volt and 277-volt versions; there’s no 115-volt option. Have an electrician confirm your service before ordering.

### Where do I get a Quest 225 manual or a 5-Series hanging bracket?

Manuals are posted on each model’s page on Quest’s website, and the optional hanging kit is sold through Quest dealers. Confirm the model and part number on the data plate first, since redesigned units use different documents.

## Related guides

- [The Best Commercial Dehumidifiers for Restoration and Job Sites](https://www.enthusiastreview.com/best/best-commercial-dehumidifier/)
- [The Best Dehumidifiers for Grow Tents](https://www.enthusiastreview.com/best/best-dehumidifier-for-grow-tent/)
- [The Best Greenhouse Dehumidifiers](https://www.enthusiastreview.com/best/best-dehumidifier-for-greenhouse/)
- [The Best Santa Fe Dehumidifiers](https://www.enthusiastreview.com/best/best-santa-fe-dehumidifier/)
- [The Best Phoenix Dehumidifiers for Restoration and Drying](https://www.enthusiastreview.com/best/best-phoenix-dehumidifier/)
- [The Best Industrial Dehumidifiers for Warehouses](https://www.enthusiastreview.com/best/best-dehumidifier-for-warehouse/)

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*Enthusiast Review researches products against DOE ratings, ENERGY STAR data, manuals, CPSC recalls and owner reviews; it does not run a test lab. Amazon links are affiliate links (tag sktiger-20).*