What State do you live in? What kind of heat? How do you get a 1/2 story?

You will find a 5 degree temperature differential between levels of the home.

The basement will be tough to heat with the t-stat "all the way upstairs". You may need some kind of separate heating for the basement as it is below grade and is much cooler than the 1st or 2nd floors. The contractor can install dampers to control air flow to the different floors.

thank you for your response. we live in TN and it will be electric heat. we call it 1 1/2 story be cause the main level is about 923 sq ft and the upstairs is just under 500 sq ft.

Amy:

I hope by "electric heat" you mean a heat pump and not electric resistance strips in an air handler.

yes it will be a heat pump. but our big concern is if one 3 ton unit is going to work and we're concerned about keeping our basement warm with the termostat upstairs. they have already put up the drywall and they were painting today. so i'm not sure what we can do at this point but any advice would be helpfull.
thank you

They can put balance dampers in the duct work to try and regulate flow - more air flow downstairs and less flow upstairs in the winter.

You could also put a few electric baseboards in the basement area and even put them on their own thermostat. Cheap to install but not real cheap to run. I think you have low cost electricity in TN.

Good luck.

okay, i just talked with the hvac guy and he said that he only put the 1 unit because with the trusses and water lines and everything else, he didn't have any place to put another unit. he did put the return in the basement, will that help? he also said that if we could come up with a way to make it better he would fix it. but i know nothing about this, any advice? sjpuld we a least make hime move the thermostat to the main level instead of the upstairs? thank you garyg for your advice.

The thermostat should be on the main level (living area). I'm assuming that "upstairs" means bedrooms. You will freeze in the summer in your living room if the stat is on the highest floor.

A return duct will help in the basement (I assume this is what you meant by "return" You could have also meant the air handler). He did put a supply duct or 2 in the basement as well, hopefully.

What about dampers in the ductwork so you can control the airflow to the different floors? You can cut back flow to the upper levels in the winter and cut back flow to the lower level in the summer. This will help balance the temperatures between levels of the house.

Ceiling fans are great at moving air. Every room in the living area and every bedroom should have a ceiling fan. These help tremendously in the summer, especially in bedrooms where it tends to get stuffy once the a/c shuts off.