register dampers

[7474]

Chicago area, had tech out to balance system on 2 story home. He closed down some of the registers (at the register not the duct damper) to increase the velocity of the air coming out. Said this would increase the throw. Would this also decrease the CFM's out of that register? What are your thoughts on this?

Thanks

[RoBoTeq]

Completely depens on the system and the individual run of duct to each outlet. Air is oportunistic. Air will go to the point of least resistance. If the duct run to the vent that is being closed is an easy point for the air to enter, then by closing off the vent some the air will simply increase velocity at the regester.

[cem-bsee]

BUT
if the joints & holes in the ductwork are not sealed, such will cause more losses --

[Shophound]

Chicago area, had tech out to balance system on 2 story home. He closed down some of the registers (at the register not the duct damper) to increase the velocity of the air coming out. Said this would increase the throw. Would this also decrease the CFM's out of that register? What are your thoughts on this?

Thanks

Closing the damper down at the register will reduce overall quantity of air delivered to that register and hence will reduce throw. However, if he was doing this to increase the amount of air delivered to other registers in the house (particularly for 2nd story registers), those registers that did not have their dampers adjusted will see an increased amount of air delivered to them, and hence will see further throw.

In two-story homes you almost always need more air for cooling purposes delivered to the upper level than the lower level. I prefer to balance airflow with balancing dampers in the supply branches near the trunk but this is not always possible or feasible. Register dampers are a fallback method and can deliver results, albeit I think they are not as effective as balancing dampers. However, if you notice improved conditions in rooms that were problematic to keep comfortable before, that's good, as long as the adjustments do not stress the equipment.

[7474]

Thanks for your replies.

All of the registers are on single trunk lines which have supply dampers. The dampers were closed down to reduce air to the trunk and the registers were closed down to "increase velocity".

[fat bob]

Sounds like he closed some dampers to decrease airflow, and closed the registers to maintain the throw. Closing the registers won't have much effect on the amount of air moving through the register until it's almost completely closed, but will increase the air speed. At least that's been my observation. In a large room you want some throw so conditioned air reaches the other side of the room. Unless there's a problem, like excessive noise or uneven temperatures, it sounds like he did it right.

[Shophound]

Thanks for your replies.

All of the registers are on single trunk lines which have supply dampers. The dampers were closed down to reduce air to the trunk and the registers were closed down to "increase velocity".

What has yet to be disclosed is did the technician's efforts solve the problem you had him out to investigate? If so, then we're merely discussing nuance. If not, then you may need him back out to do some further digging. There could be more involved than we've been told, and your tech is the best source for further discussion.

I will offer that closing down on register dampers will alter the pattern of air that emerges from the register face. Without knowing your register type and placement within the rooms there's no answer for whether this is an adverse matter or not. Your comfort in each room is a better indicator than any technical matters you might mull over, IMO.

[7474]

What has yet to be disclosed is did the technician's efforts solve the problem you had him out to investigate? If so, then we're merely discussing nuance. If not, then you may need him back out to do some further digging. There could be more involved than we've been told, and your tech is the best source for further discussion.

I will offer that closing down on register dampers will alter the pattern of air that emerges from the register face. Without knowing your register type and placement within the rooms there's no answer for whether this is an adverse matter or not. Your comfort in each room is a better indicator than any technical matters you might mull over, IMO.

Shophound,
Thanks for the replies.

I have not had an opportunity to test the adjustments, hasn't really been that hot (at least in my book).

I had no problems with the tech, he was very knowledgeable and spent a great deal of time adjusting the system. I was only wondering if dampering down the second floor vents at the register was/is the best move. As you said most 2 story homes require more air to the second floor.

My only thought was that dampering down the registers to increase the velocity would only decrease the amount of CFM to each adjusted register. The registers were adjusted down both at the supply damper and the register and measured with a handheld device to register "about 400 fpm at each register."

As you questioned, I have yet to be able to experience the results of his adjustments.

Thanks again.

[dash]

Let's wait and see if you have an inprovemnet.

Closing the dampers at either point reduces air flow flow.

Setting the velocity to 400 fpm ,is only helpful if the duct susyem was designed correctly to have that value,otherwise it's a "rule of thumb"

The cfm's is what colls the room,not the velocity,throw is a minor factor as well.