Venmar Ventilation. Kubix heat- and energy-recovery ventilators are designed for condominiums and small homes up to about 1,000 square feet. With its cube shape measuring less than 16 inches on each side, the unit can be easily concealed in a closet or above a hot water tank to save valuable space, the company says. The line comes in five models, four of which are Energy Star–qualified. 800.567.3855.