Make-Up Air
VMASS — Variable Make-Up Air Supply System
Constant-pressure make-up air and indoor air quality balance for high-exhaust building envelopes.
VMASS (Variable Make-Up Air Supply System) is Earthcore's engineered make-up air platform for the X-VENTISO mechanical venting system. It continuously replaces the air removed by high-volume exhaust so the building envelope stays at net-zero pressure — keeping appliances drafting correctly, doors easy to open, and indoor air quality within spec.
Unlike fixed-volume make-up air units, VMASS modulates supply airflow in real time against the active exhaust load using constant pressure-differential monitoring, holding pressure to a 0.02" w.c. (5 Pa) deadband as fans stage up and down.
What is VMASS?
VMASS stands for Variable Make-Up Air Supply System. A make-up air system introduces fresh outdoor air to replace air exhausted by mechanical venting, kitchen hoods, fireplaces, or process equipment. Without adequate make-up air, a building depressurizes: exhaust fans fight against negative pressure, combustion appliances can backdraft, and indoor air quality degrades.
VMASS is the variable, self-balancing answer to that problem. Rather than supplying a single fixed volume of air, it measures the pressure difference between inside and outside and adjusts supply airflow moment to moment to match whatever the exhaust system is actually doing.
How VMASS works
A pressure-differential sensor monitors the building envelope against a reference. As X-VENTISO exhaust inductors and motorized dampers stage up under load, VMASS opens its modulating supply path to introduce matched make-up air; as exhaust falls, it throttles back. The control loop targets a 0.02" w.c. (5 Pa) deadband, tight enough to prevent both depressurization and over-pressurization.
Every VMASS component ships with Molex quick-connect wiring, so supply dampers, sensors, and controllers land on the same pre-wired harness as the rest of the X-VENTISO platform — no field wiring errors. A 0–10V input lets a building automation system (BAS/BMS) command or supervise the unit where whole-building control is required.
Why constant-pressure make-up air matters
Depressurization is the root cause of the most common venting complaints: smoke rollout from fireplaces, pilot outages, whistling doors, and stale, humid interior air. These symptoms appear precisely when exhaust demand is highest — exactly when a fixed make-up air unit is least able to keep up.
By matching supply to exhaust continuously, VMASS protects combustion safety, preserves indoor air quality, and keeps the envelope neutral across the full operating range, not just at one design point.
Integration with X-VENTISO power venting
VMASS is designed to operate as part of a complete X-VENTISO system alongside end-line exhaust inductors, motorized dampers, and programmable controllers. Because supply and exhaust share the same modular, pre-wired architecture and control logic, the two sides balance each other automatically instead of being commissioned as separate systems.
Earthcore's engineering team provides submittal support to size VMASS for a project's exhaust profile, duct geometry, and envelope tightness.
Specifications
- Control strategy
- Constant pressure-differential modulation
- Pressure deadband
- 0.02" w.c. (5 Pa)
- Automation inputs
- 0–10V BAS/BMS, dry-contact enable
- Wiring architecture
- Molex quick-connect, 100% pre-wired
- Supply airflow
- Variable, matched to staged exhaust load
- Function
- Net-zero envelope pressure, IAQ protection, backdraft prevention
Applications
Multi-fireplace residences
High-performance homes with several fireplaces or a large linear unit, where simultaneous exhaust would otherwise depressurize the living space.
Tight, high-performance envelopes
Well-sealed buildings with little natural infiltration that cannot passively replace exhausted air.
Commercial kitchens & hoods
Spaces with high-CFM exhaust hoods that require matched, tempered make-up air to keep hoods capturing and doors operable.
Process & laboratory exhaust
Fume-hood and process-exhaust environments where envelope pressure and air quality must stay within a tight band.
Frequently asked questions
What does VMASS stand for?
VMASS stands for Variable Make-Up Air Supply System. It is Earthcore's variable make-up air platform for the X-VENTISO mechanical venting system.
What is a make-up air system?
A make-up air system supplies fresh outdoor air to replace air removed by mechanical exhaust. It prevents the building from depressurizing, which protects combustion appliances from backdrafting and keeps indoor air quality stable.
How does VMASS keep the building at constant pressure?
VMASS continuously measures the pressure difference between inside and outside and modulates supply airflow to match the active exhaust load, holding the envelope to a 0.02" w.c. (5 Pa) deadband as exhaust fans stage up and down.
How is VMASS different from a fixed make-up air unit?
A fixed unit delivers one set volume of air regardless of demand, so it under- or over-supplies at most operating points. VMASS varies supply in real time to track exhaust, staying balanced across the full range rather than at a single design point.
Does VMASS integrate with a building automation system?
Yes. VMASS accepts a 0–10V BAS/BMS input plus dry-contact enable, so it can be supervised or commanded by a building management system while still self-balancing on its own pressure loop.
What problems does insufficient make-up air cause?
Too little make-up air causes envelope depressurization: fireplace smoke rollout, pilot and combustion backdrafting, hard-to-open doors, whistling, and poor indoor air quality — usually worst when exhaust demand is highest.
Is VMASS part of the X-VENTISO system?
Yes. VMASS uses the same modular, pre-wired Molex architecture and control logic as X-VENTISO exhaust inductors and dampers, so supply and exhaust balance each other automatically as one integrated system.
How do I get VMASS sizing or engineering support?
Earthcore's engineering team provides submittal support to size VMASS for your exhaust profile, duct geometry, and envelope tightness. Contact X-VENTISO by Earthcore to start a project.