A VERY QUICK LESSON IN RESIDENTIAL HVAC DUCT SYSTEM DESIGN. * BOWER PERFORMANCE - Before designing/evauluation a duct system, a designer will look at the manufacturer blower performance data of the FAU (forced air unit, the proposed furnace/air handler) to determine at what ESP (External Static Pressure) can this FAU perform under to deliver the desired CFM (cubic feet per minute of air flow). This ESP will become the SYSTEM design target. Generally speaking, the manufacturers design standard blowers to achieve 400 CFM per TON of "rated air flow" (3.0 Ton furnace = 1200 CFM) at .5 inches of water column. The standard blowers have a performance curve with a steep drop off in performance. For example, going from .5 to .7 ESP (higher the number the more resistance) you might see a 170 CFM drop in performance, while going from .7 to .9, still just a .2 change, you might see a 270 drop. Variable speed blowers performance curve drop is more gentle, though often under estimated by uninformed designers. * DEDUCT THE KNOWN PD OF THE DEVICES THAT WILL BE IN THE AIR STREAM FROM THE DESIGN ESP. - A designer will now look at everything in the air stream that creates resistance, except for the actual ductwork. We refer to the resistance as PD (pressure drop). The list of devices would include the indoor cooling coil, electric heaters, filter, grilles, registers, dampers, etc., everything external to the FAU, but again, not the ductwork. Every one of these devices have manufacturer data to draw from to get the rated PD at the design CFM. Coils and filters have the greatest PD and need to be carefully selected. (The PD through that 5" media that is being proposed could be .14 or as high as .38 depending on the actual size and amount of CFM that will be moving through the filter. Keep in mind the rated PD is when the filter is clean. The PD goes up as the filter loads up.) The designer calculates the total PD of all of the devices in the air stream then subtracts the PD from the system design ESP. This will give the designer the amount of availabe ESP to design the duct system to. At this point his notes might would look something like this... Design Blower ESP (Typically at .5) Minus Coil PD Minus Filter PD Minus Register PD Minus Return Grill PD Minus Damper PD Equals available ESP to design the duct system All the numbers would come from the manufactuer product data - they are not guesses. * CALCULATING TOTAL EQUIVALENT LENGHT - in a residential duct systems, it is not the running footage, but the equivalent footage of all the fittings and transitions that create the majority of the resistance (PD). ACCA Manual D (duct design) has EL (equivalent lenght) ratings for every type of connection, fitting and transition a duct run will take. The designer needs to look at your duct system layout (size does not matter at this point) and determine the TOTAL EQUIVALENT LENGHT (EL) of the entire duct system. For example, if I understand your Return Air #1 duct, the running lenght is around 28'. I estimate the TEL to be in the 120'-200' range. For example, depending on the type of fitting that was used to create the "split", each "split" would have a rating between 15 EL to 50 EL. Two "splits" would equal 30 EL to 100 EL. If the "splits" are connected directly to each other the resistance increases. * TIME TO SIZE THE DUCTS - Unless he is using software like Wrightsoft or Elite, a designer will use a "ductulator" to size the ducts. The ductulator looks like a slide rule. There are ductulators for metal ducts and ductulators for flex duct - the data is different. All of the numbers on the ductulator with regards to CFM are based on 100 EQUIVALENT LENGHT. BEFORE looking at the ductulator to begin sizing the ducts, the designer must perform a simple calulation to determine which number on the ductulator scale to use based on the TOTAL EQUIVALENT LENGHT of YOUR duct system. (Hint: Asking the contractor to show you this simple formula is a way to quickly determine if he knows duct design or not. If you don't KNOW the formula, you do not KNOW duct design.) He will then select/confirm duct sizing based on CFM and FPM (velocity) requirements. * TIME TO GO - I need to get on with my day. I hope you found this helpful. This is a very, very short and over simplification of the design process, which is dynamic in nature as opposed to linear. My estimate is finding a residential HVAC contractor who KNOWS duct design is maybe 1 in 5 at best. Good luck.

"I think" is not good enough unless you like to part with your money. When I have been walking around the Maryland area, not far from you, I see a lot of heat pumps. The low temp performance is steadily improving so don't depend anecdotal reports from people with units that are a few years old. The number of outside walls has nothing to do with the physics of heat pump low-temperature performance, but everything to do with heat gain and loss calculations. More outside walls = more capacity, not different type of equipment. The US DOE has work sheets to help you calculate the relative costs of operating gas heat vs. heat pumps with your current utility rates (as well as cooling costs with different equipment efficiency).

How UV Air Scrubbers Work. https://www.newcentralairconditioner.com/ This is essentially the same technology hospitals are using to disinfect rooms. An Air Scrubber uses the same sanitizing power to inactivate airborne contaminants. They are so effective they are used in hotels, cruise ships, hospitals, schools, major league ballparks, and even the pentagon. The Air Scrubber is installed within your HVAC system. It’s typically placed on the supply side of the ducts, downstream from the blower. Oxygen and water molecules from the air enter the purification unit and pass through the honeycomb matrix. Using a UV light and proprietary catalyst the molecules are then transformed into safe, yet powerful oxidizers and once released the molecules become supercharged purification oxides which seek to rapidly destroy up to 99% of contaminants, fungi, mold, viruses and odor causing bacteria leaving the air cleaner and healthier. Once installed there are no filters to change and no maintenance required. Benefits of Air Scrubbers. They mitigate mold: In humid climates, such as Arlington’s, your home needs a strong defense against mold. And one place mold thrives is in your ductwork. Ducts are dark and cool and moisture in the continuous stream of air creates the perfect breeding ground. The Air Scrubber prevents mold bacteria from spreading beyond the evaporator coil, where outbreaks commonly develop. Fresher air: Mold carries with it a foul, sweat sock-like odor. The Air Scrubber neutralizes mold spores before they have a chance to stink up your home. Healthier air: People sensitive to mold exposure can experience symptoms such as allergic reactions, sneezing, red eyes, runny nose and even severe reactions such as shortness of breath and even asthma attacks. The Air Scrubber renders mold spores inert, making the air safe to breathe. Beyond mold: Air Scrubbers also tackle pollutants such as volatile organic compounds

Let me restate what you posted. You have a 2-story house that has a total of 1600 sq. feet. The first and second floors are evenly divided at 800 sq. feet each. Part of the second floor has attic insulation of R40, and the other part has R19 insulation. Your windows are either single pane or leaky, or both. You have a 2 ton condenser that was installed 2 years ago. You did not replace the furnace. No information on what was done with the coil or line set. You did not state what city in Minnesota you live near. The highest design temperature in your state is 88 degrees, so I assume that what should be used. How did the contractor determine the size of the condenser? If I have stated the information of your house correctly, then my initial reaction is your AC is undersized. If the insulation were up to minimum standards, and the windows were double pane and tight, you may be able to cool the house to 75 degrees with a 2 ton, but even that would be a stretch. I recommend upgrading the attic insulation on the R19 side. Consider installing new windows on the sunny side of the house. Use blinds to block as much sun as possible. This will help but not completely solve the problem.