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Split vs. Package HVAC

We are moving to Albuquerque, NM and have purchased a 25 year old townhouse. It has two stories, 1,910 sq. ft, 10 windows, flat roof, faces south and has a joined unit (townhouse)on each side. We want to replace the original HVAC - gas furnace, refrigerated air 4 ton unit. Three contractors have provided estimates. One of the three is making a very strong case for a packaged unit - one where all elements are packaged and placed on the roof. The reason for this is the available cfm flow is 1,200 and the new unit reguires 1,800. The other two contractors 'think" they can open the restricting neck of the ducting that is causing the problem and use a conventional split unit. Should I be concerned about using a pkg unit? It all makes sense but it's new enough to me that I thought I better ask.
Thank you for your thoughts.

John Christiano
Re: Split vs. Package HVAC

Packaged rooftop systems are, in some ways easier to install. Everything is done at the factory (refrigerants & piping). You will need some sort of curb on the roof but that's just housekeeping. There is a single power connection as opposed to wiring both the compressor and the air handler. They also free up floor space in the house since everything's on the roof.

The nice thing about packaged rooftops is that they have handy options.....

Economizers which can use outside air for cooling on those marginal days when it's warm inside but cool outside. This feature also freshens the house and greatly improves indoor air quality.

Optional motor sizes if you need a bit more push for the long duct runs.

Staged gas or electric heat.

If a bedroom is just below this unit, get a sound isolation curb.

One disadvantge with a rooftop unit is that you will have to pay a rigger to get it up there. Expect an 18-20 year lifetime.

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