Does anybody have a formula or suggestions for calculating the heat load of forced ventilation through an HRV?  Specifically, I'd like to figure out the practical difference (as far as load on my heating system) between using a standard HRV with about 74% sensible effectiveness vs. upgrading to a dual core HRV with about 95% sensible effectiveness, given the same air flow.

Thanks.

Before changing units, compare apples to apples using HVI certification, qualify airflows and electrical use.  Many air exchangers test their units at the lowest possible airflows to come up with big numbers that are not practical, or at the airflow you will be using.  Unless units are independently HVI certified, the numbers are unsubstantiated.  Qualify same efficiency number descriptions by HVI.  There are two numbers given on this report; Sensible Recovery Efficiency and Apparent Sensible Effectiveness (usually @ 10 points higher), and these will be qualified by airflow, for example 74% Sensible Recovery Efficiency @ 120 cfm.  The unit you may be looking to buy could be 95% Apparent Sensible Effectiveness @ 64cfm.  They might actually be rated closer than you think.  Look at watts per cfm. and Total Recovery Efficiency (@95F, a summer number).  You may be spending a lot of money for very low return or even a loss.