A New Approach to Makeup Air in Tight Homes

A new product addresses a tricky problem in well-sealed homes: when exhaust fans, range hoods, or several of them running together pull air out of the house, something has to replace it. In a tight home, there aren't enough gaps and cracks for air to sneak back in, so the house can become depressurized. That's a real safety concern if you have a fireplace, woodstove, or an older water heater, boiler, or furnace that vents through a chimney rather than being sealed to the outside — depressurization can pull smoke or combustion fumes back into the house instead of sending them outdoors.

Earthcore, known for its Isokern fireplaces, has introduced a system called VMASS (Variable Makeup Air Supply System) as part of its X-Ventiso venting line. It works by measuring the air pressure difference between indoors and outdoors and automatically adjusting how much outdoor air it brings in to make up for what's being exhausted. Instead of relying on someone to remember to crack a window before lighting a fire or running a strong exhaust fan, the system responds on its own as exhaust loads change.

If your house has been tightened up through weatherization or air sealing work, and you have a fireplace, woodstove, or fuel-burning appliance that vents through a chimney, this kind of automatic makeup-air control is the sort of equipment worth asking about when you're planning ventilation or combustion-safety upgrades.