Question about Rinnai Direct Vent Space Heater

[Mike Roy]

We recently closed on nine units in Wiscasset, ME - 3 townhouse style triplexes.  All units are identical at 960 sq. ft., 480 sq. ft. on each floor.  The downstairs consists of a living room, kitchen and 1/2 bath and upstairs is 3 bedrooms and a full bath.  These modular buildings were constructed in 1993 and are fairly well insulated.

My goal is to convert the existing central heat for each building into individual heat and have the tenants pay for it.  I have done this successfully in the past with another building and rents really didn't suffer.

Each building is currently on a central boiler, and I recently had a contractor tell me that he could split off the existing boiler to service one unit and offered the option of boilers for the other two units or a Rinnai EX38 downstairs and an electric water heater in the basement.  The Rinnai option is about $10k less than going with boilers and are also easier to maintain with longer expected life, though I understand I'll be replacing water heaters from time to time.  Right now, I'm leaning toward the Rinnai.

My question for BP is addressed to anyone in a colder climate that has either attempted or has insight about heating a two floor unit with a single Rinnai space heater on the first floor.  Is this a practical solution?

I'm also considering a Rinnai downstairs and electric baseboards upstairs to be used solely as backup during the coldest months.

Thanks very much!