You can set the air balance in most ERV/HRV to be positive or negative. I think the rule of thumb is that they almost always are set to provide slight positive

You can set the air balance in most ERV/HRV to be positive or negative. I think the rule of thumb is that they almost always are set to provide slight positive pressure, to avoid drafting e.g. gas appliance exhaust into the house, but I'm not a HVAC expert, just someone looking into them for residential usage.