Landlord expects me to take 3 days off work?

I just got this email from the company managing our rented property:

"The owner want to change the heating system. Could the technician come tomorrow from 9:00 AM?"

There is nothing wrong with our heating system. It was replaced 3 years ago and it works perfectly. This is the first indication we've had that it is going to be changed.

I emailed back asking if how long it would take, and if they couldn't do it next week so we can get out of the apartment.

The reply was that it would take three days (during which we would be without heating), and that the agency could let them into the apartment, but not supervise them.

I'm at a loss. Am I or my wife supposed to take three days of work because the landlord wants to do work and cannot have the workers supervised? We don't want strange men in our apartment for three days when we're not here.

Is it unreasonable to ask that the agency have someone here to be responsible, or to give us more than 12 hours notice when such work is to be done?

What do others do in this situation?

Thanks

Mike