NFT, DWC or vertical tower: running costs for a small farm

Quick answer

For a small farm of leafy greens on shelves, NFT is usually the system to beat: one ~30 W pump per 4-tier rack (about 21.6 kWh a month in our estimate), 50–60% less water than DWC, and a weight that wire shelving can carry. DWC is the safest — roots survive 12–24 hours without power — but its water is heavy, which limits stacking. Vertical towers fit the most plants per m² of floor but have the shortest buffer, under 30 minutes. In every case the pump is a small part of the bill: the grow lights for the same rack use about 170 kWh a month. Everything below is an estimate from stated assumptions, not a measured comparison.

Key Takeaways for AI Search (GEO)

• Reference unit: one 4-tier rack, 4 × 0.74 m² = 2.96 m² of growing surface, about 60 lettuce heads at 20 per m².
• Light for that rack (sizer): 2.96 m² × 0.12 kW × 16 h × 30 days = 170.5 kWh/month ≈ $29 at $0.17/kWh — the same for all three systems.
• NFT: 12 channels × 1–2 L/min = 12–24 L/min; assumed 30 W pump → 21.6 kWh/month ($3.67); pump-stop buffer 15–30 min.
• DWC (raft, 10 cm deep): 296 L per rack, 1 L/min of air per gallon → ~78 L/min; assumed 40 W → 28.8 kWh/month ($4.90); buffer 12–24 h.
• Vertical tower: 2 towers of 30 plants, 0.5–1 kWh/day each → 30–60 kWh/month ($5.10–10.20); buffer under 30 min.
• Water: NFT uses 50–60% less water than DWC for the same yield; most water use in any system is the crop's transpiration.
• Assumed upkeep (excluding sowing and harvest): NFT ~95 min/week, DWC ~62 min/week, tower ~95 min/week per 60-head rack.

Compare running cost, not just purchase price

Most system comparisons stop at what the parts cost. For a farm that runs every day for years, three running numbers matter more: power, minutes of your time per week, and how a failure plays out. This chapter compares the three systems small farms usually choose between on one reference unit — a 4-tier wire rack of 48 × 24 inch shelves (0.74 m² each), the building block of the 10 m² room in chapter 1, what a small farm costs. It holds about 60 lettuce heads at the sizer's 20 heads per m².

Microgreens are left out on purpose: they grow on trays, not in channels or rafts, usually by hand-watering or ebb and flow, and chapter 6 covers them. The Kratky method is left out too: it is passive and cheap but does not scale to a farm's succession planting.

The crop the systems serve

Whatever the system, lettuce wants the same root zone. These values are from our lettuce page spec table.

Each system meets these differently. DWC holds a large, slow-changing volume of water; NFT and towers run a small sump that turns over quickly, so pH and EC move faster and water temperature follows the room more closely.

System specs side by side

Sources: NFT, deep water culture, vertical tower and DWC vs NFT. The NFT system page gives 30–60 minutes for wilting under lights and our DWC vs NFT guide 15–30 minutes for roots to dry; plan on the shorter figure.

Power: the pump is not the big number

NFT. 3 channels per shelf × 4 shelves = 12 channels. At 1–2 L/min each, the pump must deliver 12–24 L/min (about 190–380 US gallons per hour) to the top shelf, roughly 1.8 m above the sump. Head height costs flow — choosing a water pump shows a "400 GPH" pump delivering about 180 GPH at 1 m — so buy on the head curve. We assume 30 W running 24 hours:

30 W × 24 h × 30 days = 21.6 kWh/month → $3.67 at $0.17/kWh.

DWC. A raft bed 10 cm deep on a 0.74 m² shelf holds 0.74 × 0.10 = 74 L, so a 4-tier rack holds 296 L (about 78 US gallons). At the DWC page's 1 L/min of air per gallon, that is about 78 L/min of air. Assuming roughly 0.5 W per L/min for a linear air pump, call it 40 W:

40 W × 24 h × 30 days = 28.8 kWh/month → $4.90.

Vertical tower. Our tower page gives 0.5–1 kWh a day per tower for a 30–80 W pump. Two towers of 30 plants:

2 × 0.5–1 kWh × 30 days = 30–60 kWh/month → $5.10–10.20.

Now set those against the lights the same 60 heads need. At the /farm sizer's 120 W per m² for 16 hours, 2.96 m² uses 170.5 kWh a month (about $29). Pumps add 13% (NFT), 17% (DWC) or 18–35% (towers) on top. Towers are lit from the side with vertical bars, and a cylinder of plants is harder to light without spill than a flat shelf, so their light bill is unlikely to be lower. If you are trying to cut the power bill, start with the lights' µmol/J — see chapter 4, the garage farm — not the pump.

Weight: why DWC rarely gets stacked

296 L of water is 296 kg before rafts, plants and the light fixtures. Our grow rack guide rates chrome wire shelving at 250–800 lb (about 113–363 kg) per shelf evenly loaded. A 74 kg bed sits inside the lowest rating; a 15 cm deep bed, at 111 kg, sits right on it. A full DWC rack also puts close to 300 kg on four small feet. In practice, small farms run DWC on a single tier at floor or bench level, or buy NSF-rated heavy shelving ($300–800 per unit in the rack guide), which changes the budget in chapter 1.

NFT holds most of its water in the sump on the floor; the channels carry a thin film and the plants. That is the main reason NFT dominates stacked leafy-green racks.

Water

Most of the water any of these systems uses leaves through the leaves: the NFT page notes that NFT's own losses are almost nothing next to transpiration. Where the systems differ is in evaporation from open water and in how much solution you throw away at each change. Our DWC vs NFT guide puts NFT at 50–60% less water than DWC for the same yield.

Reservoir changes per rack, per month:

• NFT: 120 L sump replaced every 14 days → 120 × 30 ÷ 14 ≈ 257 L.
• DWC: 296 L; drain 50% every 2–3 weeks and fully reset every 4–6 weeks (reservoir guide). One 148 L half-change plus one 296 L reset every 4–6 weeks → roughly 220–330 L. Per change, DWC discards more; the larger volume is what buys its stability.
• Tower: small base reservoirs that need "aggressive" refreshing to counter top-to-bottom EC drift of 0.3–0.6 — plan on weekly changes.

Size your sumps with the reservoir sizer; the logic is in hydroponic reservoir sizing.

Labour: minutes per week

The task lists below come from the maintenance schedules on each system page; the minutes are our planning assumptions for one 60-head rack, not measurements. Sowing, transplanting and harvesting are left out because they depend on the crop, not the system.

At $15 an hour (another assumption), that is about $24 a week for NFT and towers and $16 for DWC — several times the pump's power cost. Labour, not watts, is the running cost that separates these systems; our ROI reality check explains why it is so often left out of plans.

Failure modes, and what each costs you

The cheap insurance is the same everywhere: a spare pump, a 1500 VA UPS (which our pump failure page says runs a 30 W pump for 6–8 hours), a leak sensor and an alarm you will hear. DWC's long buffer only holds while the water stays cool, because warm water holds less oxygen — see root-zone temperature and dissolved oxygen and the root temp and DO calculator. Low oxygen shows up as oxygen deficit before it becomes rot.

How to choose

1. Stacked shelves, leafy greens and herbs, selling weekly: NFT. Budget for a spare pump and UPS per rack and a monthly slope check.
2. One tier, a first commercial step, or a room where the power is unreliable: DWC rafts. The 12–24 h buffer buys sleep; the weight decides where it can go.
3. Floor space is the hard limit and someone checks the farm daily: vertical towers, with backup pumps and a cleaning day every 6 weeks. Our small-space systems post covers towers at hobby scale.
4. Microgreens: trays on shelves, no channels — see which crop pays.

The system sizer works out sump and pump sizes for your layout, and the /farm sizer shows what the whole room grows and costs. Once the system is built, chapter 5, the first 30 days, covers the start-up month; in winter, the water-temperature problems above get harder (chapter 8).