A HEPA air scrubber, sold in the same box as a negative air machine, pulls room air through a filter stack and either returns it clean or ducts it outside. Hire runs roughly $60 to $140 a day and $180 to $400 a week, plus filters. Sizing is arithmetic: room volume times the air changes you want, divided by sixty.
The sizing sum, in one line
Multiply length by width by height for cubic feet, multiply by the air changes an hour the job calls for, then divide by sixty to get the cfm you need. A room of 20 by 15 by 8 ft at six air changes wants about 240 cfm, so one 500 cfm machine covers it with margin for filter loading.
What HEPA means on the ticket
The federal construction silica standard defines a HEPA filter as one at least 99.97 percent efficient on particles of 0.3 micrometers. Anything a branch calls high efficiency without naming that grade is a lesser filter. Ask which grade is fitted, and whether spare filters travel with the machine.
Negative pressure needs the room sealed
Run the machine with its outlet in the room and it recirculates and cleans. Duct the outlet outside and it holds the room below the pressure around it, so dust stays put when a door opens. That second job only works if the sheeting, tape and doorway zip are done properly first, so budget the plastic.
Filters are consumable and they are billed
A prefilter clogs within hours on drywall sanding, and a HEPA cartridge lasts a season of light work or a week of heavy. Yards charge for what you use, so ask the price per filter before the job starts and change the prefilter often: a blocked stack drops airflow long before anyone notices.
Questions people ask about hepa air scrubber
Air scrubber or negative air machine, which do I need?
They are the same box used two ways. Run it with the outlet open in the room to filter the air, or duct the outlet outside to hold the space at negative pressure. Renting one machine covers both, provided the ducting is on the ticket.
Will an air scrubber handle concrete dust?
It handles what is already airborne, and it is the second line of defence rather than the first. Cutting and grinding silica bearing material calls for water or on tool extraction at the source, and the scrubber deals with what escapes that. Hiring one without the tool controls is doing the job backwards.
How many machines does a large room need?
Work out the cfm from the volume and the air changes, then divide by the rating of the unit the branch stocks. Two smaller machines at opposite ends usually move a room better than one large unit in a corner, because the air actually crosses the space.
Can I run one on a normal socket?
Most units in the 500 to 2,000 cfm range draw modest current and run on a standard 15 or 20 amp circuit. Two of them on one circuit with a vacuum and a site radio will trip it, so give the scrubber its own outlet and leave it running overnight if the job continues tomorrow.