I'll see if I can find it (again), but there is a paper on-line discussing the parameters in the algorithm used in the AHRI method of predicting system performance... EDD is definitely an input. In months where I am not using any oil except when heating during defrosts, I can not see any change in my oil tank level over a month or two time period... and whatever cumulative amount of oil that is used during say 10- 15 minute defrosts would be lessened if there were fewer defrost cycles, but the question would be what is THAT difference. I would be interested in hearing from you in the trade what the most common methods of system failure are. Specifically with a focus on what components fail due to increased "wear and tear" due to timed defrost? From reading posts here it seems that mostly non-repairable refrigerant leaks leads the reported list followed by compressor failure... I believe most compressors carry a 10 year replacement warranty???? If I compare the operational wear and tear due to starting and stopping between an oil furnace and a heat pump in heating mode, the oil furnace cycles on and off much more frequently than the heat pump. Yet, my oil furnaces have typically lasted 30-40 years. Just thinking out loud.

Most of the Infinity/Evolution units that have been installed in my subdivision as replacements have been the 16 SEER versions. For the price increase, the 19 SEER probably isn't worth it, and I think the reciprocating compressor is fine in almost any situation. I like the lower capacity on stage 1, and both compressors (scroll or recip) would have a 10 year warranty. The 25HPA6 quote also communicates with the Infinity system and has a scroll compressor, but it's lower capacity is much higher, so less run time in low stage. I'm assuming the 5 year warranty is through the company itself. Usually it is 1-2 years. 10 year labor warranty coverage usually runs around $6-700. Hard to tell what can happen, but labor costs can easily make the extended coverage pay for it. If the $700 is feasible upfront to you, then you may really thank yourself down the road. Most do not go with the extended warranty I imagine, but if you can, it certainly will only be beneficial. Let us know if you have any more questions.

I have 4 returns, MBR, hallway ceiling upstairs, on the stairs on the main floor and in the basement on the wall between the utility room and the living space. The guys quoting said they looked like good locations, as well as the location of the thermostat being good. The wifi thermostat is the carrier infinity thermostat with wifi support. Lets you set it up or adjust remotely, but either way it is the infinity one. I asked about the 95% and they said that based on the cost (1.06 per ccf) that there would be no payoff. Do you think otherwise? The unit cost is about a grand more and requires a more complex install with cost. I am not against it, but the people quoting certainly were. Do you know how I can get some numbers that would help me make the decision? what makes you like #2 more than the amana? Would the carrier be significantly quieter/better? The labor warranty would be much more than the amana from my understanding. (1200 vs 400 for 10yr) Basement tends to be cold by a few degrees in the winter. Load calc will definitely be in hand before I allow anything to be installed.

12" return is almost definitely too large for the basement. I have a 6" return in my basement, and I have actually found it to draw ~200-240 cfm (using a barometer) -- plenty in my case with just a few supply outlets. In your case, I have no way of knowing for sure, but I assume it's piped directly (or near) to the inlet of the furnace blower compartment, in which case there is a lot of pressure and it's sucking in a lot of air and making the basement quite negative (not a good thing). So your basement return in that state may have been drawing close to, if not more than, half of the return air the entire system requires. Is the basement floorplan open to the rest of the home or closed off? If typically closed off, I wouldn't be surprised if the basement door had a tendency to close itself when the system was operating. I suppose putting cardboard over half of the grille is one way to reduce its intake capacity. Your older furnace does not (presumably) have a variable speed blower that will vary its RPM in order to maintain a specific CFM setting. That means that while you are noticing more airflow from the rest of the returns throughout the home, in totality your system is receiving less airflow -- no, not a good thing considering your ductwork is likely undersized to begin with. You have decreased its return capacity. To get the SAME (total) airflow from the rest of the returns throughout the home that were not previously drawing as much air generally requires the system to operate at an increased static; with older PSC type blower motors (non variable-speed), this results in decreased airflow. Hence variable speed motors are often termed "constant CFM" as they can adjust (increase) their speed to maintain a constant airflow (cfm) when subjected to as much as 0.8-1.0" of external static pressure (vs. conventional blowers max. of 0.5", which many duct systems are nowhere close to achieving despite it being the standard "design" figure). You can think of the ESP number as a measure of resistance to airflow, in a sense. The fact that you say the (supply?) ductwork is now much warmer is both concerning and telling. It is unwise for me to say much more than that as I am not there to evaluate your system design and give an accurate assessment of the ductwork design/layout, etc. But it suffices to say, with the info you've provided us, your return ductwork is now more restrictive, which would exacerbate any existing airflow issues. You do say it met the set point without tripping the high limit. Please let us know how the system performs as it gets colder out and the system runs more often in its present state. I would like to ask what made you consider replacing the systems (and proceeding to get 8 proposals) in the first place? Are there functional problems with the existing equipment (besides most likely being oversized) or other comfort issues? By now we have at least established that it is likely the existing equipment is a bit oversized and the existing ductwork is marginal -- but that is (unfortunately) exceedingly common on most residential construction. Are you after more efficiency, better comfort, both? It helps us to help you when we know more about your current system's performance. Lastly, I would not factor online reviews into your decision too much. An air conditioner or furnace is not like most appliances (such as a refrigerator) in that the installation practices and quality can make or break even the best equipment selection. There is a good chance that many (but not all) of the negative reviews you read were due to installation errors. This post was edited by ryanhughes on Fri, Nov 22, 13 at 9:51