HVAC people, how do you fix air flow issues?

[mindless1]

I wonder how much actual planning is done in a typical HVAC duct system these days. Is it done in the field by the grunts doing the work or is it scienced out before hand or what? Yes, I know I've really oversimplified all that.

That's going to depend on who is doing it. At a reasonably large company I worked for a quarter century ago there was a master certified architect that did the design based on blueprints, but then on-site there was another master and helpers in varying degrees of competence that had to alter designs on the fly for various reasons like ending up on a job after the plumber and sometimes electrician had already done their work.

There isn't a lot of planning needed however, you just run the ducts up as directly as you can get away with it which is dictated by floor joists, wall locations, register placement near a window or across from the return. The design of the house determines how it's going to end up unless the plumber or electrician did something goofy, and of course with central air you may want to place the stack next to a floor drain.

Keep in mind that many times a home builder did many in the area and only uses a few designs popular for the era so in many cases the whole design is just a repeat of the way it was done the last time on another home with same layout.

 

[Greenman]

I wonder how much actual planning is done in a typical HVAC duct system these days. Is it done in the field by the grunts doing the work or is it scienced out before hand or what? Yes, I know I've really oversimplified all that.

My home in Michigan if FA with floor registers and wall mounted returns. The airflow creates more noise than I like. The other morning it was unseasonably cold at 17 F and the system after coming out of setback eventually decided to ramp up to the highest blower speed and having not heard that in a long, long time I had to start checking to see if there was a fire in the basement because the noise was an actual roaring sound. There are no dampers anywhere although the main line does get smaller the farther away it is from the furnace and airflow does come out of all of the registers.

In Florida, we have an air handler literally stuffed in a closet. The front of the place is over-cooled to the point of it being cold in order for the back half to be comfortable. The conditioned air is taking the path of least resistance. Very short runs to the front of the condo and long runs to the back. Up in the attic are several distribution boxes but they all appear to be sized the same but I'm not interested in walking around up in there stooped over to really scope it out. I had the HVAC guy out to take a look at the system to establish a baseline (new purchase for us) and he was willing to go up there and look around but he was vague and non-committal on what if anything needed to be done or could be done. What I'm wondering is if it is worth it to have them investigate further.

Google "manual j" and "title 24". It's actually a rather involved process.

 

[boomerang]

Google "manual j" and "title 24". It's actually a rather involved process.

My question was actually more rhetorical in nature. What I'm truly wondering is if I can find a local contractor interested in investigating the airflow issues at our condo. And I understand that nobody can answer that question for me here. I'm just going to have to call around once we get down there.

 

[LegendKiller]

We bought a new house and had some problems with balancing for the first year. Builder's AC guy came out twice to rebalance, once the first summer, then the winter, and now this winter we have had no problems. It was initially so bad that we considered either retrofitting dual zones or buying a second furnace and AC unit to give us real dual zone.

A few rooms at the end of trunks still get a little cooler but it isn't a huge deal at this point.

I'd hire an HVAC guy to come out and rebalance, he'll measure and look at everything and adjust accordingly.

 

[crashtech]

Most people, including HVAC installers, overlook a critical element of the system: repressurization at the end of distributions. If the design of the system is incorrect, you basically can't fix it and no amount of tweaking will significantly help unless you rip out the main distribution areas.

This actually works very similarly to electron flow in a conductor with a terminated load at the far end. In a nutshell, even if you increase the blower motor torque by 5x, it may not actually increase airflow because the air has to pressurize after outlets in the main distribution duct. The last pick-off is often placed at or near the end of the main duct, which is incorrect. If the duct doesn't extend far enough past the last pick-off, the inside of the main duct will never pressurize and air transfer will be slow.

Your observations may not be related to this particular type of issue, but I really wouldn't be surprised if they are related because this is a very common mistake even in houses built over the last few years.

Do what everyone else suggested first and then evaluate the air pressure at various registers. If there's no noticeable change, you're probably looking at a bigger issue such as the one I mentioned above.

I'd like to gain a better understanding of what you are describing here, but haven't had luck googling it. Would you perhaps link to a diagram and/or some reading material on this particular type of problem?