Keep in mind that a variable speed blower lets you go up to 1.0" of static pressure. That can help a LOT with marginal ductwork.
And yes, it's reasonable enough for companies to charge to do a full Manual J&D. That can be a couple hours of work, which isn't reasonable on a free estimate. You can pay someone to do it and then have a set of calculations to shop around to everyone, or you can accept bids based on rules of thumb that say Manual J&D will be used for final equipment and ductwork selection. While rules of thumb are not a good way to select equipment, they're close enough most of the time that many contractors use them to bid. So long as they come back and do the full measurements and calculations before actually installing the unit, it's just fine if they want to bid on rule of thumb and eat the difference if the calculations end up calling for a different size unit.
Finding talent in Houston
You CAN find people in the Houston TX area to do tests for ESP (external static pressure), airflow and the other things recommended by pros on this site. I live near Houston to the West in zipcode 77441, and have done so. You can identify some of these HVAC pros by this website:
Believe it or not the local Home Depot on Hwy 99, is connected with an HVAC company which promised to me to use ACCA methods thoroughly. At least you have the option to complain to Home Depot if they behave wrongly, and they take that seriously.
Best of luck -- Pstu
Can go to 1.0" wc,but at what cost?
Typical wattage,3 tons ,indoor fan;
The other problem is ,you may still have the runs farthest away from the indoor fan not getting enough air flow,while the closer ones are howling.
[Edited by dash on 08-16-2006 at 08:56 AM]
reffered to above is not static,it FR(friction rate)
yeah your right i didn't even notice that.