Contemplating adding an ADU (Accessory Dwelling Unit) to an existing reside nce in Portland, Oregon. In California this was called a "Mother-in-law Ap artment".
Unit to be in basement. Main floor already has owner and two room mates sh aring utility (gas and electric) bills. ADU will be 2 bedrooms and a large open kitchen-dining-family room. Separate street entrance. Approximately 800 square feet.
HVAC guy says electric heaters are out of the question due to utility costs . Next best would be 3 mini-splits (different sizes). Down side is the hi gh initial equipment cost ($4-5 k) plus installation. Also it's kind of wa steful since the air-conditioning capabilities of the mini-splits will rare ly be used.
Most favorable would be keeping the existing furnace and adding additiona l ducts for a separately zoned system. Low initial cost, only one piece o f equipment to maintain, easily serviced and easily replaceable.
Said furnace is gas and I need advice on how some of you have split the uti lity bill. To date the heating (furnace-air conditioning and water heater) averages about $70 per month. If we follow this model (splitting cost) wh at prevents the basement tenant from cranking up the heat to 90°, either on purpose or carelessly while away at work?
There are plenty of solutions to separate the electrical charges (second se rvice, private meter etc.). However don't see an easy way to split out the bill for a single gas furnace that is zoned to take care of two areas.
I'm sure some of you have already solved this. Subject is new to me.
BTW, would it be legal for me to place a temperature sensor (full disclosur e to tenant) in their unit and ding them for heating above a certain temper ature?
All suggestions greatly appreciated.
Ivan Vegvary