1.5 story new construction w/ basement, one A/C system

[MUPPPP]

Hello, all. First time poster.

We are looking at a new home. It is a 1.5 story house with a walkout basement. I have always heard that if you have a 2 story house, it is imperative to have separate heating/cooling systems for the main and second floors. This house only has one five ton (RUUD 13 SEER) A/C unit outside (main two floors are 2800 sq feet and basement is 1800). There is one blower/furnace in the basement, and one thermostat on the main level. The system is not zoned.

The builder and HVAC guy said it is designed so that it has a chase that runs all the way to the attic before giving off any ductwork to the upper floor, and there is a separate chase for the main floor and basement. There is a manual damper that can be opened/closed incrementally to drive more of the air to the 2nd floor if needed.

I am afraid that when it is 95 degrees outside (in Missouri), we'll have the main floor thermostat set at 72, the basement will be 62, the main floor will be 72, and the upstars will be 85 or something. The builder said that the adjusting the damper would keep this from happening.

Also, one weird thing that we noticed is that there aren't any air vents in the upstairs walk-in closets or bathrooms . One of the bathrooms is a Jack-and-Jill configuration with two separate vanity rooms and an adjoining toilet/shower room. There is also a walk-in closet coming from one of the vanity rooms. I asked the builder why and he said those rooms didn't need it b/c they were interior rooms and would normalize with the temp of the adjacent rooms. I am skeptical about this.

Does anybody have any idea as to how this system will work? Because of our skepticism, we are wanting to word our contract to say something to the effect of this: If the upstairs can't get cooled to 75 degrees on a 90+ degree day with the main floor and basement temperature being within 5 degrees of the 2nd story temperature, that the builder must solve the problem by putting in a dedicated 2 ton ac unit w/ separate thermostat in the 2nd story.

Will this wording work?

Thanks in advance for any advice!

[Kevin Weaver]

add the Honeywell Tru-zone system and put a wireless thermostat in an upstairs bedroom. 2 zones, mainfloor/basement and second floor. As far as the closets and bath ares, those rooms could have a vent added fairly easily from what you described

If you get the zone system, don't let them do the balancing bypass damper system, instead, put the right size damper in for the second floor and a slightly undersized damper on the first floor so it has a little bypass to it.

A zone system will be like having 2 systems but you will only need to service one. ENJOY

[MUPPPP]

Thanks for the advice. Is it difficult to add a zoning system to a system that is already installed and walls are finished? Is it something that will just be installed in the ducts downstairs where the blower is, or are they going to have to cut up walls and whatnot? I think I recall reading something about a zoning system that it is not possible to do this unless the ductwork to the 2nd floor can handle >70% of the total air capacity of the system. Is this true? How much could this potentially cost?

[SkyHeating]

If there is a manual damper already it should not be difficult to add zoning later but anytime you are adding after the fact it is more expensive. For a house of that size i would always recomend zoning but you have to pay for it. The house has a 5 ton load the heating guy did the right thing(assuming he did a manual J and D) now its up to you as to how comfortable you want to be and how much you want to pay for that comfort. Do you plan on paying more for a second dedicated 2 ton system for the downstairs and a 3 ton for the upstairs or do you think it should be the same price? Would you be willing to pay more for zoning? Any calculation the HVAC does has a built in fudge factor, usually that is a 6 degree temperature difference between floors, that is "normal" if there is a manual damper it also assumes YOU will properly adjust it to balance airflow from season to season.

[teddy bear]

Any concerns for the fresh air ventilation to purge indoor pollutants, indoor air circulation/filtration, and maintaining <50%RH during wet cool weather? These are indoor air quality and comfort issues.
Regards TB