I do not know what size our existing heat strips are. I am assuming the lowest possible, it is the same unit the builder placed in the home and it doesn't appear the original home buyers upgraded much. No idea about heating the place yet, we just moved into the home in March and our winter months here last year were very mild so I think we already had the a/c on. As far as cooling goes, we do not spend a lot of time up there yet. Our master is downstairs and the loft area is in under construction. It does not ever feel very cool to me but I really think this more impacted by the large windows in the great room and high 20 ft ceilings that open up to the loft as well as the age and capacity of the unit. I received another quote from another company here in town and the gentleman recommended the XR15 as a cost effective alternative to the XL15i. The quote he provided included replacing our downstairs system as well (both up and down with XR15's, 2.5 ton for upper and 3.5 for lower with variable speed handlers and Honeywell thermo) and didn't break up the prices in two. The total cost was $10k. I cannot get to the estimate right now to provide part numbers. However, I am now completely confused as he did not include a separate line item for the heat strips? We also discussed upgrading the insulation in the attic space because of the cooling issue etc. He confirmed what I origianlly thought and that is the insulation is the minimal for the standard back in 1999. He oprovided a quote to upgrade with R-38 of around $1800.00. I feel like the more I try to learn about the HVAC system the more confusing it gets. What exactly is the function of the heat strips? Is there any reason his quote wouldn't include a line item for same? Thanks for your help.

The 17 SEER 2 speed is the value leader in this instance. The 20 SEER variable would provide the best comfort at the most economical operational cost view point, if your utilities are above 15 cent per KWH then this would be a no brainer. At a 15 cent operational cost it would take you 21 years to recoup the cost difference. At a 10 cent operational cost it would take you 31 years. This is in comparison to the units offered and doesn't reflect the additional savings you will get from the equipment you currently have. So comparing this to your current utility usage could put the pay back much faster than the 17 SEER system would provide. Sizing: yes sizing is important, but in terms of variable inverter systems they run via load matching so sizing is only important in terms of duct sizing / air flow distribution and so on. The variable speed / inverter AC will only supply the cooling need to match the load. So over sizing of these systems is really impossible, they don't start up in high stage. They start slow - ramp up and then match the load of the structure. While it's more costly to over size an inverter system, there are certain manufactures that sell only 5 ton condensers and 3 ton condensers. There are settings that can limit these machines to either 4 ton capacity or 2 ton capacity. I suspect this trend will only continue as HVAC industry looks to cut costs in the number of SKU's required. With that said sizing varies all day. Even a properly sized AC system can be oversized during specific time periods. A 2 speed AC is probably over sized somewhere around 50% of the time. A single speed AC is over sized 80-90% of the time. A variable inverter (full inverter) never over sized. A 5 step variable inverter rarely over sized maybe 5% during seasonal changes.

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.

Sizing can be less of an issue when you have multiple units. Because each unit is controlled independently, provided of course the unit itself is not over sized for the area in which it serves resulting in excessive short cycling. In your case 3 ton plus 2 ton isn't necessarily equal to 5 tons of cooling... unless you drive those thermostats really low. By having two systems with total capacity of 5 tons (which, most of the time this would be oversized for a 1700 - 1800 sq ft structure) has a few advantages. 1. You have the ability to use one system only during low heat days or set the opposing unit higher. The unit set higher only runs if load conditions warrant.... meaning if it's not hot, the thermostat controlling the unit does not call... the unit can not run without a call... 2. Utility bills can be much less... because you rarely use both systems at the same time. You run the bedroom system when you sleep, the other when you're awake. If you have a home office in one the bedrooms you may need to rethink things a bit. 3. Extra capacity for when it's hot out. When it's hot you have the capacity to cool the home. (even while entertaining guests --- additional people add heat) Remember heat waves come, heat waves go... a so call 'properly sized' AC system is essentially properly sized roughly 10% of the time... especially if that system is a single speed AC system. Alot of people I come across like to sleep cool. So for that reason I doubt I would change the configuration of the space. Once you realize what you have, the choices you make are mostly budget type concerns. Essentially a set up like this runs like a 2 stage system. This kind of subject is above the pay grade of many... choose your contractor wisely. I service the Katy, Texas area.