Use Ratio Utility Billing System for gas??

[Shannon Brill]

Hello BP!  I currently own a duplex and have a question regarding using RUBS for gas usage.  RUBS is already in place for water, but here's the issue with gas -- both units use gas heat (equal sqft), however only one unit has a gas range/stove (the other unit has electric).  How to you equitably charge the tenants for seasonal usage (high in winter/low in summer) and when there's unequal gas appliances between the units?  I'm unable to come up with a solid solution here (adding a separate gas meter is too expensive.)  I'm hoping that I'm not the only one that's encountered this. TIA!