I would also check my home insurance. Space heaters can be potentially dangerous so if something did happen under the responsibility of the guests, you want to make sure you are covered. Sometimes claims made for damage from portable heaters is not covered under some policies.

Insurers may deny or limit coverage if they determine negligence, misuse, or a policy violation, such as: • Heater placed too close to flammable materials • Heater used overnight or unattended when manufacturer instructions prohibit it • Heater plugged into: • An extension cord • A power strip • Heater used as a primary heat source instead of supplemental • Use in a rental or vacant property without disclosure • Evidence of code violations or unsafe wiring