There's no central heat, only resistance baseboard, so you're going to have a hard time keeping renters with how high the utilities will be.https://www.zillow.com/homedet... 5 trailer trailer park.

If so, heat rising is expected.

On Time Experts, Air Patrol AC& Heating etc.

Assume the roof needs replacing, plumbing leaks everywhere, there are no appliances, no heat...

Older heating systems can be up to $10k per unit. 

Last Year I bought a 4 family property in AC.  3 of those units get their heat from one furnace. 

Storage areas can include built-in cabinets, closets, attic space, and even outdoor sheds, etc.Laundry: Including a laundry area and machines is a big bonus for tenants, as they compare that with apartment living where they would have to use common laundry machines that require payment.HVAC: Make sure to include an effective dual heating & air-conditioning system to service the ADU, so your tenant is comfortable in the unit.Kitchen island: It may be difficult to squeeze in a kitchen island in a small ADU, but it’s a big bonus if you can make the space.

I am getting estimates on replacing a old oil boiler with a new gas boiler to heat the rental house.

I have never replaced a heating/cooling system that was operational.

This house's basement was flooded to the ceiling, submerging the oil burning furnace, heating oil tank, security system panel, electrical panel, and water heater.