mnk716 (My Page) on Wed, Jan 15, 14 at 16:56 I have a one zone 3ton unit AC system for a 2400sqft house built in 2006. House is very tight. I was very concerned when it was proposed and the HVAC contractors said it would not be a problem to maintain a temperature i am comfortable with. i like it at 70-71 degrees during the summer and it has always maintained that temperature. the thermostat is one 2nd floor in the hallway by the stairway. no complaints and the 1st floor gets about 1-2 degrees cooler than upstairs. i am convinced that one unit can maintain the temperature if it is installed correctly. I live in CT and spend about $160-180 @ month during the summer with AC. Wow - that's what I am talking about! Has it ever broken down? Or if it did what is your philosophy? Posted by countryboymo: I upgraded my system and downgraded the size to 3tons and my strips to 10kw. At zero the heat pump might be off but it still cycles on the strips. At 10 below the strips run constantly but maintain temp. I still have a considerable amount of sealing to do in the attic and more insulating....A quality envelope and decent system that is zoned will keep money in your pockets. Again - inspirational!

I think if you foam the attic, you solve all the problems with your last house. I built recently at the NC coast and we had 2 two ton heat pumps. It cost $1000 to upgrade both to seer 15. That also gave a better warranty. I think seer 15 is nearly always worth it in our climate. Now foaming the attic makes the payoff for seer 15 longer but still probably reasonable. Now if you told me you were building extremely tight and really minimize the East and West windows and shade the south ones, then seer 15 might not be worth it. That is why these questions are so hard to answer. Everything is ... it depends. But a decent generality is that if you have to have East and West windows in SC, seer 15 is worth it. One could build a house with a $100 a year a/c requirement in SC for seer 13 and then it wouldn't be worth upgrading to seer 15. I know you've decided to foam the roof deck but I always have to be the skeptic. My electric bills last year were $350 total for the 3 hot months. I am absolutely sure that foaming the attic would have saved some money. I am pretty sure it would be less than $50 a year. While we a/c longer than 3 months, those bills also include everything else electric. So almost 1/2 those bills are not a/c so I think they are a pretty good estimate of the total annual a/c use. Foam salesman will of course differ in their estimates. But the foam mostly only helps the upstairs system and my house (and probably your house) has 2/3 of the a/c use downstairs. Even if the foam saved 40% of my upstairs bill - it is about $50. Now foam also saves in winter but is often justified in a/c use. Comfort upstairs would be helped by rigid foam on the knee walls. This is a far greater ROI although honestly it still probably exceeds 10 years. I think you might be overkilling it to overcompensate for your last uncomfortable house.

Mike_Home - Thank you for the answers and advice. Here are some responses and follow-up questions. 1. SEER/EER - your answer is what I had been slowly understanding that these numbers are what drive the efficiency numbers. Rough calculations comparing my older 10 SEER unit to a 14 and 16 SEER unit plus using 1 year of energy bills, show a potential electricity improvement of $184/year for the 14 and $238.31 for the 16. Of course this is all dependent on a quality install as well as proper ducts, etc. as you've outlined in other points. 2. Payback will be uncertain as I was relocated for work. Not sure how long we'll be here and at this point, the energy savings per year is still important. 3. Understood. Before my research, I didn't realize that the furnace played such an important role in airflow. 4. My zoning explanation might have been poorly stated. The gist of what was mentioned, was that based on proper zoning, the more efficient airflow distribution within the home may allow for a 4 ton condenser. The condenser potentially wouldn't have to push air through all of the ducts at the same rate. Does that logic track with your experience? 5. Appreciate thermostat advice and handling all the features, etc. 6. The annual maintenance contract was from the contractor providing the detailed Goodman quotes. Participating in the yearly maintenance contract covers 100% of repair costs (Contractor backed, not OEM), includes a 10 year replacement warranty, and there are no dispatch or service fees for service calls. The replacement warranty is the full replacement of the failed unit rather than just repairing under the 10 year labor warranty with Goodman. If I don't do the yearly maintenance contract, there is no replacement warranty. Ever heard of this? The contractor (Goodman quotes) may have mentioned "calculations" at one point but I don't remember hearing about them doing a manual "J" load calc. As far as I can tell, Title 24 doesn't require the J calc. It does require a duct leak test performed by a certified 3rd party HERS testing company. This is required on ALL HVAC projects in CA. Rebates are only available as part of CA's Home Upgrade Program. This program has required testing and upgrades on items like ducts, whole home envelope, attic insulation, etc. I will go back to two of the contractors and ask them about performing the calculation. I am looking to replace the whole system at this point to make sure the equipment is compatible and most efficient. Goodman is making me increasingly nervous, especially with the Class Action lawsuit that was just set back last week based on a judge's ruling... As for the use of a different coil with the Goodman equipment, it seems to be very common with Goodman quotes (based on board postings like this). I think there is a relationship or commercial connection between Goodman and Aspen to drive the high use with Goodman systems. I don't know the true specs on the Ruud equipment, I was guessing a bit; I will ask for the models, etc. Thanks again!

The biggest problem with HVAC zone systems is knowing when to choose it as a solution and when not to. Some HVAC companies it's about "sell, sell, sell" whether or not it works... there's more money in "sell, sell, sell" --- when it's only about money? So does the comment above mean I do it for free? No. If you think that you are reading things that aren't there. New construction? best to choose separate systems 9 times out of 10. In order for a zone system to work, you have to know what you are doing. Most HVAC companies staff (the techs they send you) are 20-30 year olds. How much practical experience could they possible have? It's best for HVAC zone systems to be an elegant solution. A HVAC zone system is a tool in the tool bag. Not all homes are suitable for zone systems. Some homes there is no other way, and in some cases complications to those problems will make an HVAC zone system design possibly more prone to problems. You have a problem now, do you want more problems. These decisions among others are decided "in person" --- so considering that becareful what information you decide upon from the internet. Just because it's here doesn't necessarily mean it's true. That said: Depending on equipment level chosen, how many different floors you have in your structure, how much room you have available... will all be factors that make you decide one way or another. From there it's in your best interest to pick a contractor that is skilled: especially when it comes to HVAC zone systems. (there's a lot of garbage out there.) (click to enlarge if necessary) I service the Katy, Texas area.