A DIY fume extractor built around a 600-800 CFM inline duct fan with MERV 16 filtration costs $150-300 and provides meaningful fume reduction for a home shop. It won’t match a commercial unit’s self-cleaning filters and certified filtration, but it moves fume away from your face and captures most of the particulate before it circulates through the shop. For hobby welders who can’t justify $1,500+ on a commercial extractor, a properly built DIY system is vastly better than welding with no extraction at all.
The honest disclaimer upfront: a DIY system is a compromise. Commercial fume extractors exist because source capture engineering is complex, and certified filtration matters for health. If you weld frequently or work with stainless, galvanized, or coated metals, buy a commercial unit. If you’re a hobby welder who runs a few hours of MIG or stick per week in the garage, a DIY extractor substantially reduces your exposure at a fraction of the cost.
The Basic DIY Approach
A DIY fume extractor has four components: a fan, a filter, ductwork, and a capture hood. Air enters the hood near the weld, travels through the ductwork, passes through the filter, and exits. Simple in concept, but each component needs to be sized correctly.
Step 1: Fan Selection
The fan is the most critical component. It needs to move enough air (CFM) to create adequate capture velocity at the hood opening while generating enough static pressure to push air through the filter and ductwork.
Inline duct fans are the best option for DIY extractors. They install in the ductwork between the hood and the filter, move adequate CFM for single-station extraction, and are readily available.
| Fan Type | CFM Range | Static Pressure | Cost | Suitability |
|---|---|---|---|---|
| AC Infinity CLOUDLINE T8 (8") | 807 CFM (free air) | 0.6" WC | $120-150 | Good for light welding |
| Fantech FG 8 (8") | 438 CFM at 0.5" SP | 1.0" WC max | $180-250 | Good, higher static pressure |
| Dayton 8" inline (various) | 500-750 CFM | 0.8-1.2" WC | $150-300 | Good, industrial quality |
| Standard box fan | 2,000+ CFM (free air) | Near zero | $20-40 | Not suitable (no static pressure) |
Critical: Fan CFM ratings are usually listed at “free air” (zero static pressure). Once you add filter resistance and ductwork friction, actual airflow drops significantly. A fan rated at 800 CFM free air might only deliver 400-500 CFM through a filter and 10 feet of ductwork. Size up to account for system losses.
Do not use: Box fans, pedestal fans, window fans, or bathroom exhaust fans. These generate high CFM at zero static pressure (no ability to push air through a filter or ductwork). They move air in open rooms but stall completely when resistance is added.
Step 2: Filter Selection
The filter captures welding fume particulates from the air stream. For DIY builds, the most practical option is a standard HVAC filter in a custom housing.
MERV 16 filters capture 95%+ of particles in the 0.3-1.0 micron range. This is the minimum filtration level for welding fume. MERV 13 (standard “high efficiency” HVAC filters) captures only 85% at this particle size range, which isn’t sufficient.
Filter housing: Build a plywood box sized to hold a 20" x 20" or 24" x 24" MERV 16 filter. The filter should seal tightly in the housing with no air bypass around the edges. Use foam weatherstripping to create an airtight seal between the filter frame and the housing. Air will follow the path of least resistance, so any gap around the filter becomes a bypass route for unfiltered air.
| Filter Rating | Efficiency at 0.3-1.0 microns | Suitability for Welding | Cost per Filter |
|---|---|---|---|
| MERV 13 | ~85% | Marginal (minimum for any fume) | $15-25 |
| MERV 16 | ~95% | Adequate for mild steel welding | $30-50 |
| HEPA (99.97%) | 99.97% | Best (but high resistance) | $80-200 |
HEPA filter caution: True HEPA filters have high resistance to airflow. Most inline duct fans can’t generate enough static pressure to push adequate CFM through a HEPA filter. If you use a HEPA filter in a DIY build, expect significantly reduced airflow. The fan must be rated for at least 1.5" of water column static pressure to work with a HEPA filter.
Step 3: Ductwork
Use 6" or 8" diameter smooth-wall duct from the capture hood to the filter housing. Larger diameter means less friction and more airflow for the same fan power.
Smooth-wall metal duct (galvanized spiral duct) is best. It has the lowest friction per foot and resists damage from sparks. Available at HVAC supply houses and home improvement stores.
Flexible duct (insulated or uninsulated) has much higher friction than smooth-wall. If you must use flex duct for the final connection to the hood, keep it under 3 feet and stretched as straight as possible. Crushed or coiled flex duct kills airflow.
Layout rules:
- Keep total duct length under 15 feet for a DIY system
- Minimize bends. Each 90-degree elbow equals approximately 5 feet of straight duct in friction
- Support duct runs so they don’t sag (sagging creates low spots where condensation collects)
- Seal all joints with foil tape or duct mastic (not cloth “duct tape”)
Step 4: Capture Hood
The capture hood is the business end of the system. It positions near the weld and creates the entry point for fume-laden air.
Simple funnel hood: A sheet metal cone or flared opening at the end of the ductwork. Inexpensive and easy to make. The opening should be 8-12 inches in diameter for a 6" duct system, creating a velocity amplification at the entry that helps capture fume.
Articulating arm: For flexible positioning, attach the hood to a section of flexible duct or build a simple arm from PVC pipe with elbow joints. This lets you reposition the hood for different weld locations. Commercial extraction arms use spring-loaded or friction-locked joints for easy positioning.
Position: 6-12 inches from the arc, to the side and slightly above. Don’t position directly above (fume rises naturally, but overhead positioning interferes with helmet and visibility).
CFM and Capture Velocity Calculation
The goal is to achieve 100-150 fpm (feet per minute) of air velocity at the capture point (hood face).
Capture velocity formula: V = Q / A
Where:
- V = velocity in fpm
- Q = airflow in CFM
- A = hood opening area in square feet
Example: An 8" diameter round hood opening has an area of approximately 0.35 square feet. To achieve 150 fpm capture velocity at the hood face, you need:
Q = V x A = 150 x 0.35 = 52.5 CFM at the hood opening.
That sounds low, but capture velocity drops rapidly with distance from the hood. At 6 inches from an 8" hood with 500 CFM flowing through it, capture velocity is approximately 100-120 fpm. At 12 inches, it drops to approximately 50-70 fpm. These are rough approximations. Actual capture velocity depends on hood shape, surrounding air currents, and the specific geometry of the installation.
The practical takeaway: More CFM is always better for fume capture. Get the biggest fan your ductwork and filter can support.
Build Cost Breakdown
| Component | Option | Cost |
|---|---|---|
| Inline duct fan (8") | AC Infinity T8 or equivalent | $120-150 |
| MERV 16 filter (20x20") | Filtrete or equivalent | $30-50 |
| Filter housing | 3/4" plywood box, built custom | $20-30 (materials) |
| Smooth-wall duct (6-8", 10 ft) | Galvanized spiral duct | $25-40 |
| Duct fittings (elbows, transitions) | Various | $15-25 |
| Hood/funnel | Sheet metal or purchased | $10-20 |
| Mounting hardware, tape, sealant | Various | $10-20 |
| Total | $230-335 |
Add $30-50 per replacement MERV 16 filter. For weekly welding, expect to replace the filter every 2-4 months.
Build Tips
Seal everything. Air leaks reduce system performance dramatically. Every duct joint, every panel seam on the filter housing, and every connection point must be sealed with foil tape or mastic. Test by holding a tissue near joints while the fan runs. If the tissue moves, you have a leak.
Pre-filter extends MERV 16 life. A cheap MERV 8 pre-filter upstream of the MERV 16 captures larger particulates (grinding dust, general shop debris) before they load the expensive filter. The pre-filter is disposable and costs $5-10. Replace it monthly.
Add a differential pressure gauge. A $15-20 magnehelic gauge across the filter tells you when the filter is loading up and needs replacement. Without it, you’re guessing. Connect one port upstream and one downstream of the filter. When the pressure drop exceeds the filter manufacturer’s recommendation, replace it.
Ground the ductwork. Metal ductwork carrying particulate-laden air can build static charge. Ground the duct system to the shop electrical ground. This prevents static discharge that could theoretically ignite accumulated particulate in extreme cases and also prevents annoying shocks.
Exhaust location matters. If you’re exhausting filtered air back into the shop, point the exhaust away from your welding area. If you’re exhausting outside (through a wall or window), ensure you have makeup air coming in elsewhere. Exhausting 600 CFM without makeup air creates negative pressure in the shop that fights against the fan’s performance.
When DIY Isn’t Adequate
A DIY extractor is insufficient for:
Stainless steel welding. Hexavalent chromium exposure limits are extremely low (5 micrograms/m3). MERV 16 filtration at 95% isn’t sufficient. You need commercial HEPA filtration (99.97%) and should still wear a respirator.
Galvanized steel. Zinc oxide fume is very fine and requires high-efficiency filtration to capture effectively.
Professional/production welding. If you weld all day, invest in commercial extraction. Your health depends on consistent, certified filtration.
Multi-station shops. DIY systems scale poorly. Two or more stations need properly engineered ductwork and fan sizing.
OSHA-regulated workplaces. DIY extraction systems don’t come with filtration certifications. OSHA inspectors expect documented equipment performance when evaluating compliance.
Improving a DIY System Over Time
Start basic and upgrade components as budget allows:
- Start with: Fan + MERV 16 filter + basic ductwork ($150-300)
- Add: Pre-filter stage for filter life extension ($10)
- Add: Differential pressure gauge for filter monitoring ($15-20)
- Upgrade: To nanofiber or HEPA pre-filter for better efficiency ($50-100)
- Upgrade: Fan to higher static pressure model for better performance through filters ($200-300)
- Eventually: Replace the whole DIY system with a commercial extractor when budget allows
The DIY system gets you started with meaningful fume reduction today. It doesn’t have to be the final solution.
The Bottom Line
Build a DIY extractor if you can’t afford a commercial unit and you’re doing hobby-level MIG or stick welding on mild steel. Use an 8" inline duct fan, MERV 16 filtration, smooth-wall ductwork, and proper hood positioning. Total cost: $150-300.
Don’t pretend a DIY system is equivalent to a commercial fume extractor. It’s a meaningful improvement over nothing, not a replacement for proper extraction equipment. Still wear a respirator while using it. Upgrade to commercial equipment when you can.
For commercial options, see our portable fume extractor guide and shop system guide. For filter information, check our fume filter types guide. Browse the fume extractors hub for all our ventilation content.