Tenant closed vents because it’s too hot !

[Peter Morgan]

Hello,

In one of my duplex rental units the ac heating and cooling is shared between both the tenants. I find the lower unit tenant somewhat peculiar, given he is in the lower unit there will be more heating need as it is much colder in the lower unit but he prefers the vents completely closed in winter and interestingly has more cooling needs during summer than the upstairs tenant. As I understand closing vents is a major engineering work that requires both an hvac technician and a contractor, but the tenant just took control and sealed some of the vents using an aluminum foil. I would like to know if it’s okay to seal completely vents using an aluminum foil as I am afraid it can potentially break down the hvac system due to undue pressure build up. I have temporarily shut down the furnace and temporarily provided portable heating units for the upstairs tenants to buy some time to find a permanent resolution

please advise.

Thanks