For penpals ryanhughes and tigerdunes: Yesterday was installation of my new Carrier 5-ton Infinity 19 HP with 58MVC100 furnace and Air Purifier. There was also some constructive revamping of my existing ductwork, feeding in my three returns. The startup person came shortly before the installers left, and everything seemed ok, but when the Infinity Controller was first switched on, the warning of high static pressure came on the screen- I think it said 1.33 at 1750 cfm (but not exactly sure if I've got that right). (If I could figure out how to do it, I could post a couple pictures if that would be at all useful.) The system has been running ok since last evening and I expect to have some people return today or tomorrow to try to figure this out. Is there anything that comes to mind as a possible cause and possible fix? Am I doing any harm by running the system until it's figured out? Thanks.

Thank you for taking time to respond. I'd say overall that our home has relatively poor insulation properties - it's basically an old brick home with lathe/plaster walls. There's little to no insulation in the walls. We did a decent job insulating the attic ceiling with loose fill and radiant barriers. I can understand why we might need more than 1.5 to 2 tons, but 3 sounds like a bit much and as you suggest, a professional load calculation seems like the prudent thing to do. Re: ducts, we'll have returns installed in each room and we won't cut off the existing ductwork, we'd simply shut the existing registers. I'm wary of tearing through plaster to install dampers in the existing ductwork. Trying to understand your comment on the 5kw heat strip ("absurd"). You think we need more supplemental heat than suggested? I figured the existing gas furnace (heat from the main floor) would mitigate the need for more heat. Any thoughts on Carrier versus Bryant? Their both owned by United Tech and I'm led to believe Carrier's more expensive just because of the brand. Thoughts? Thanks again.

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

There has been nothing said here by either the OP and other posters to make me change my mind. The system quoted is overkill for the location. The pricing is absurd. Dealer is taking advantage of his customer. However if OP continues to go down this path, at least get a price from Carrier's sister company Bryant who offers exact same equipment. And FSQ is correct, you want the 005L Infinity air handler for best matching performance/efficiency numbers. I have no idea what the Carrier dealer is even thinking. See below. 7175593 ActiveSystems CARRIER AIR CONDITIONING CARRIER AIR CONDITIONING 25VNA836A**30 FE4AN(B,F)005L+UI 1050800600 34200 10.50 17.50 34200 10.50 23000 1 HRCU-A-CBYes 236646 There are less expensive ways to get dehumidify on demand. I suggest requesting a price on Carrier's Performance 16 HP system with the FV005L var speed air handler. I am done here. Good Luck. You may need it. IMO