Joe, 1. I generally have one supply register per room, if I need a 7" duct instead of a 6" duct to carry the extra cfm for the next sized unit, then the cost for that run is only a few dollars more and no more labor. There may be one or two more supply registers needed for the whole house. Returns; I do centralized returns for open areas and one per room that can be closed off (bedrooms for instance) so again no real increase in labor cost for returns. 2. I am confused on your loop sizing strategy, but I see that here you are saying the next larger unit for the same house will need longer loops. So I assume that means that the 80% unit will have shorter total loop than if the next larger unit is used. Shorter loop for the same load means colder ewt during 100% of heating, which means lower heating capacity and lower COP. There is a loop cost increase then between the 80% and 100% strategy 3. There is only a $50 list price difference between the ND038 and the ND049 4. So all in all, the significant price difference is in the cost of the looping so I think the argument is more about loop size than unit size. (perhaps not) But longer loops always mean lower operating cost. 5. When the load reduction is taken into account, and the increased production the longer loop length has on satisfying the same load, then my statement is not contradictory. ( I am not talking about larger units per se, but meeting 80% of the load or 100% of the load.) By reducing the load, the unit and ductwork become smaller to satisfy 100% of the load. The loop length might be the same as others would use for 80% of the NON reduced load, but with the reduced load there is less btu per foot of loop extracted from the ground so the ewt is higher. Look at the heating capacity changes based on ewt for the same unit. 6. In the NE of this Country, the rater community has come to the conclusion that geo does not produce the efficiency promised and they are actively trying to exclude geo from Energy Star rated homes and are down rating the performance stated by the manufacturer. The reason is that most geo units are being designed and installed to meet 80% of the load, have 30% propylene glycol antifreeze, and low loop temperature of 20F at peak load. This creates a system with high pumping energy and low heating capacity and large electric supplemental heat. The raters started looking at geo performance because the Energy Star rated homes were not performing to the predicted level of efficiency because these systems were operating at COPs close to or less than 1/2 the COP in the published AHRI data. This is my biggest motivator to spend my time challenging you and others on the 80% of load is the proper sizing philosophy. Consumer confidence is low when the respected rater tells the builder and homeowner that the reason their house is not performing as expected is because the geo system is not really energy efficient at all and they wasted their money. These same raters push the new air source heat pumps as the real high efficiency heat pump systems. It is our own fault if we continue to push low first cost over operational cost as the design criteria when the reason the customer wants geo in the first place is to have the lowest operating cost possible. 7. I do look at the comments with an open mind. However I believe I am justified in challenging the accepted wisdom that 20% undersizing of geo systems is the proper sizing. If you took a unit that was sized to meet 80% of the heating load and increased the loop length, then you could get the same unit meeting 100% of the load . I have been trying to address this question of proper sizing, should it be 80% or 100%. I have not seen any demonstration of the efficacy of the 80% of load sizing strategy, with the accompanying lower loop length; but, rather statements about big trucks vs small cars and only a $100 difference in operating cost that sound good but do not deepen the discussion.