On 4/9/15 5:59 PM, Ivan Vegvary wrote:
Contemplating adding an ADU (Accessory Dwelling Unit) to an existing residence in Portland, Oregon. In California this was called a "Mother-in-law Apartment".

Unit to be in basement. Main floor already has owner and two room mates sharing 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 high initial equipment cost ($4-5 k) plus installation. Also it's kind of wasteful since the air-conditioning capabilities of the mini-splits will rarely be used.

Most favorable would be keeping the existing furnace and adding additional ducts for a separately zoned system. Low initial cost, only one piece of equipment to maintain, easily serviced and easily replaceable.

Said furnace is gas and I need advice on how some of you have split the utility bill. To date the heating (furnace-air conditioning and water heater) averages about $70 per month. If we follow this model (splitting cost) what 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 service, 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 disclosure to tenant) in their unit and ding them for heating above a certain temperature?

All suggestions greatly appreciated.

Ivan Vegvary


Is there a problem using gas heaters of the *In The Wall* type,
usually on a shared wall between 2 rooms, running off a separate meter
? Commonly seen in apartments/condos in milder climate areas.