daffer I think your strategy is right on target. The only question is whether you want dual fuel(var spd furnace backup) or an air handler(with strip heat backup). With an air handler and strip heat, you would need to check electric panel/service to see if you have capacity to handle backup strip heat. If not, cost to upgrade electric service. Here are three best configurations with var speed air handler. I like the numbers of the Carrier Infinity 16 HP with Infinity controller best. It has better BTU numbers both heating and cooling. 552846 Active Systems XP19 SERIES LENNOX INDUSTRIES, INC. XP19-060-230* CBX32MV-068-230* 58500 12.05 16.30 53500 8.25 32800 1481762 Active Systems XL19I WEATHERTRON TRANE 2TWZ9060C1 2TEE3D65A1 56000 9.90 15.75 51000 8.50 31400 1250425 Active Systems INFINITY 16 PURON HP CARRIER AIR CONDITIONING 25HNA660A30 FE4ANB006+UI 60000 11.10 15.30 57500 9.00 34200 You know 5 ton is correct size? I would check Duke Power and see if they offer any rate incentive for HP heating. 410 refrigerant is the way the market is moving. IMO

Thanks for the response. I'll try to address each point (let me know if I skip anything). A local business (Lexington, KY) provided the quote. Monthie Mechanical. I do have the load calculation on-hand. It was designed around: Summer: 72F Indoor / 95F Outdoor Winter: 68F Indoor / 8F Outdoor RH%: 30 Grains The Heat Pump model is: 25HNH542A003 The Air Handler model is: FV4CNF005T00 Technically the Manual J math came out to 3.69 tons. They recommended dropping to 3.5 tons vs going oversized with 4 tons. The quote is for a 20 KW strip model: WKFCEH3301C20 The thermostat in the quote is "TP-PHP". It looks like that's the "Edge" you're referring to? The quote also includes a new drip pan (30x60), 30AMP circuit panel addition, and new concrete Condenser pads for the Heat Pump. The current supply is capable of 1500 CFM, but the current two return are only capable of 1200 CFM. The plan is to either enlarge one of the two current returns or add an additional third return to bring the return CFM up to 1500 CFM. Let me know if you need any more info. :)

So there is no "correct" amount of tons needed per square foot. It should be based on load calculations based on orientation and shade and location. For a mobile home, there is no right answer. If the house can stay at 74 degrees on a hot day then the unit is big enough. The usual design temp is 75 so getting to 74 is a luxury. Now if some days, the temp can't get below 80 then you have an issue. You don't actually mention what the interior temp is. I am guessing that it isn't cold enough for you. I am going to guess that it isn't really the a/c's fault. I think your infiltration or insulation is the problem. For the amount of windows that I've usually seen on a mobile home, 2 tons should be fine for a new home.

Thanks again, neo. Yeah, that is odd about the SEER rating dropping. Looking at Contractor #2, for instance. Q1 and Q2 are the same, except Q1 has a 21 SEER condensing unit and Q2 has a 17 SEER. Why would cooling capacity go UP with the 17 SEER? Same coil, same blower, different condensing unit. #1 21SEER condenser 96.6% furnace Coil AHRI: Cooling Capacity 57000 BTuh EER Rating: 12.20 SEER: 15.5 #2 17SEER 96.6 Furnace Coil AHRI Cooling Capacity 57500Btuh EER 12.3 SEER: 15.5 Then Contractor 1, Q2 has the same 17 SEER condensing unit, but with an 80% furnace. Also, this quote has a slightly different coil number, 6124 instead of 6024. See here that the SEER goes up to 16.5, and cooling capacity increases as well. AHRI Cooling Capacity 59500Btuh EER 13.2 SEER 16.5 --- I'm not trying to hit every rebate I can. It's just frustrating that some are just barely out of reach with what seem to be pretty efficient systems. You really have to go all out to get them.