Home and Auto Simple AC tips to help keep your cool this summer

**Bugeater** · 07-23-2011, 09:27 AM

Quote:

Originally Posted by Donger

I wouldn't think that shutting of the supply vents to unused rooms would cause any issues. I would think that the volume of air that the fan pushes is what it is, and that closing off supply vents would simply allow that air to be pushed to the vents that are open.

Am I wrong?

That's what I always thought as well, but I was told by several people who are a hell of a lot smarter than me that it's not the case.

**Rain Man** · 07-23-2011, 09:34 AM

Quote:

Originally Posted by Bugeater

That's what I always thought as well, but I was told by several people who are a hell of a lot smarter than me that it's not the case.

That's surprising.

**Bugeater** · 07-23-2011, 09:40 AM

Quote:

Originally Posted by Rain Man

That's surprising.

Yes, it is. The way it was explained to me is your fan can only move x amount of air through whatever size your duct is, and the only way to move more air is with a more powerful fan, or a larger duct.

**Donger** · 07-23-2011, 09:50 AM

Quote:

Originally Posted by Bugeater

That's what I always thought as well, but I was told by several people who are a hell of a lot smarter than me that it's not the case.

I don't see why that would be the case, though.

**Rausch** · 07-23-2011, 09:51 AM

Quote:

Originally Posted by Bugeater

That's what I always thought as well, but I was told by several people who are a hell of a lot smarter than me that it's not the case.

It saves on the ac unit but it doesn't save on the bill.

So, you pick. More of a push on the AC to save a few bucks on the bill (shortening the life of the unit) or lengthening the life and overall production of your unit while paying a bit more.

**Dave Lane** · 07-23-2011, 12:47 PM

Quote:

Originally Posted by Bugeater

That's what I always thought as well, but I was told by several people who are a hell of a lot smarter than me that it's not the case.

Well they are wrong or they are taking a simplistic view in a very small house. Assuming you have plenty of ducts shutting off a room or two that are not being used will not hurt your system. Too little airflow can cause the coil to not get warm enough from the passing air which can be a problem.

**Bugeater** · 07-23-2011, 12:55 PM

Quote:

Originally Posted by Dave Lane

Well they are wrong or they are taking a simplistic view in a very small house. Assuming you have plenty of ducts shutting off a room or two that are not being used will not hurt your system. Too little airflow can cause the coil to not get warm enough from the passing air which can be a problem.

No, it won't necessarily "hurt" the system, my point is that it's not going to make the remaining rooms much cooler, if at all. And you're not really going to save much money by shutting those rooms off.

**Dave Lane** · 07-23-2011, 01:31 PM

Quote:

Originally Posted by Bugeater

No, it won't necessarily "hurt" the system, my point is that it's not going to make the remaining rooms much cooler, if at all. And you're not really going to save much money by shutting those rooms off.

Not true. If you think of it in simplistic terms imagine a 5 ton AC unit that has to cool 3000 sq ft. Now imagine all ducts are closed off but one 500 sq foot room (with the thermostat there). It will cool that room much quicker and cycle off much faster (other considerations of wear and tear aside for the moment).

Now is it safe and is it worth the savings is an entirely different argument but all things being equal smaller sq footage = energy savings.

**Bugeater** · 07-23-2011, 01:55 PM

Quote:

Originally Posted by Dave Lane

Not true. If you think of it in simplistic terms imagine a 5 ton AC unit that has to cool 3000 sq ft. Now imagine all ducts are closed off but one 500 sq foot room (with the thermostat there). It will cool that room much quicker and cycle off much faster (other considerations of wear and tear aside for the moment).

Now is it safe and is it worth the savings is an entirely different argument but all things being equal smaller sq footage = energy savings.

Well that goes against everything I've been taught, which is a fan with x amount of power can move y amount of air through a z size duct, and anything else would require breaking the laws of physics.

**Dave Lane** · 07-23-2011, 02:00 PM

Quote:

Originally Posted by Bugeater

Well that goes against everything I've been taught, which is a fan with x amount of power can move y amount of air through a z size duct, and anything else would require breaking the laws of physics.

AC units normally only move a fraction of the air through a pipe it is capable of. Of course my scenario might part your hair as you walked by the duct but the amount of air flowing through a duct is nowhere near what its capable of.

Stewie · 07-23-2011, 02:03 PM

Quote:

Originally Posted by Dave Lane

AC units normally only move a fraction of the air through a pipe it is capable of.

What? A/C units move no air.

**Bugeater** · 07-23-2011, 02:07 PM

Quote:

Originally Posted by Dave Lane

AC units normally only move a fraction of the air through a pipe it is capable of. Of course my scenario might part your hair as you walked by the duct but the amount of air flowing through a duct is nowhere near what its capable of.

You're right that it's not the size of the duct that limits the amount of air moving through it. The speed of the fan is what does that.

Chief Roundup · 07-23-2011, 02:49 PM

Quote:

Originally Posted by Dave Lane

AC units normally only move a fraction of the air through a pipe it is capable of. Of course my scenario might part your hair as you walked by the duct but the amount of air flowing through a duct is nowhere near what its capable of.

Well there again if the duct work is sized properly for the system by the installer then there won't be much of a fraction left over. If someone oversizes duct you will not get much air flow into your home. And your effenciency is no good.
And it won't "part your hair" if you close off that extreme amount because the blower will not be able to move that much anymore.

Stewie · 07-23-2011, 01:57 PM

Quote:

Originally Posted by Dave Lane

Not true. If you think of it in simplistic terms imagine a 5 ton AC unit that has to cool 3000 sq ft. Now imagine all ducts are closed off but one 500 sq foot room (with the thermostat there). It will cool that room much quicker and cycle off much faster (other considerations of wear and tear aside for the moment).

Now is it safe and is it worth the savings is an entirely different argument but all things being equal smaller sq footage = energy savings.

That will get to temp quick, but won't remove humidity. Removing humidity is the main point of an A/C system.

Chief Roundup · 07-23-2011, 02:45 PM

Quote:

Originally Posted by Dave Lane

Not true. If you think of it in simplistic terms imagine a 5 ton AC unit that has to cool 3000 sq ft. Now imagine all ducts are closed off but one 500 sq foot room (with the thermostat there). It will cool that room much quicker and cycle off much faster (other considerations of wear and tear aside for the moment).

Now is it safe and is it worth the savings is an entirely different argument but all things being equal smaller sq footage = energy savings.

No this will not work like you are thinking at all.
Blower are sized by the size of the system that they are put into.
If you have a 5 ton Air Handler it has a motor and a blower wheel sized to move 2000 cfm's of air. If you restrict or block off half of the registers in your home it will make the blower slow down because it can't move that air. Then that air becomes a restriction. When the blower slows down it won't even be able to pull half of the normal amount of air. Also when you do this and it can't move enough air across the coil and that will cause the coil to freeze up. Along with all of this you are making that motor work hard pulling more amps, costing your more energy, as well as the motor uses that air to keep itself cool.