Upstairs floor vents = useless?

[colton]

I had a HVAC guy do a walk thru of my 2219 sq. foot home and we have a semi-open loft upstairs with two floor vents. I told him that our current system hardly pushes any cool air up there - in fact, the vent feels cool, but there wasn't anything blowing from it. He said there was probably nothing he could do about that and that the vents were most likely going to be "decoration". What?!! To make matters worse, he said that a dedicated a/c in my attic that blows directly into the loft area would be the best choice and not worry about the floor vents at all.

Please, could someone make some sense of this suggestion? I don't really mind having a dedicated 2nd floor a/c in my attic that blows into the loft, but saying that a 2.5 ton unit in my garage can't blow ANY cool air through the floor vents seems fishy to me.

Help!

- Colton

[aircooled53]

Originally posted by colton
I had a HVAC guy do a walk thru of my 2219 sq. foot home and we have a semi-open loft upstairs with two floor vents. I told him that our current system hardly pushes any cool air up there - in fact, the vent feels cool, but there wasn't anything blowing from it. He said there was probably nothing he could do about that and that the vents were most likely going to be "decoration". What?!! To make matters worse, he said that a dedicated a/c in my attic that blows directly into the loft area would be the best choice and not worry about the floor vents at all.

Please, could someone make some sense of this suggestion? I don't really mind having a dedicated 2nd floor a/c in my attic that blows into the loft, but saying that a 2.5 ton unit in my garage can't blow ANY cool air through the floor vents seems fishy to me.

Help!

- Colton

Better call another company to have ductwork,coil and blower checked. A 2.5 ton for 2200 sq.ft. is a little small,and if the length of the ductwork from furnace or air handler is over 30ft to the loft .

[colton]

Yes, it's definately over 30ft from the furnace to the loft floor vents. Would a 3 ton unit be better suited to push air into the loft?

- Colton

[trane]

Originally posted by colton
Yes, it's definately over 30ft from the furnace to the loft floor vents. Would a 3 ton unit be better suited to push air into the loft?

- Colton

No, installing a zoned system or a seperate system for the upstairs are your only options that will work and not be a waste of money.

[colton]

So, he was right about suggesting a separate unit to cool the upstairs loft? Is it normal for air not to reach ducts upstairs if its more than 30ft from the furnace - or should I still request duct work?

Thanks!

- Colton

[amb4081]

Duct sizing and balancing is essential.

A system for each level is ideal. However, a properly sized unit with correct ductwork and balancing can work fine. I have been able to adjust dampers at two story homes to provide more even airflow and temperatures on all levels. The difference is they were 3 1/2 ton systems or larger.

[suemarkp]

You haven't posted enough information to answer the question, and your HVAC tech may not have looked into things enough either (he should measure the total static pressure). I have a similar problem at my house. All ducts have an "equivalent length". Things like 90 degree bends or takeoff may be 60', a register boot 80', how many takeoffs are down stream in the main duct add length, and then the actual length of the straight pipe itself counts.

I have one upstairs duct run that has an equivalent length of about 360 feet. Most of my others are about 200 feet or less. The two ducts on this 360' equivalent run hardly blow. You can increase the airflow to these by mostly closing some of the air vents in the downstairs rooms (or install balancing dampers). However, this will increase static pressure and reduce total air flow. And some rooms downstairs may then be too hot, so pick a large open room with multiple vents if possible like a family room/living room/kitchen.

To see if this approach is possible, you need to know how much air your system is flowing now and what is the static pressure. If the air flow is marginal for its size, or the static is about maxxed out, then you have no solution except for more ducts upstairs or replace the air handler with a more powerful one that can work at higher static pressures.

A quickie calculation is to assume a minimum airflow of 350 CFM per ton and assume that each register will flow 100 CFM if on 6" pipe or 150 CFM if on 7" pipe. If you have plenty of duct capacity for your system, then you can try closing off a few registers and see what happens. Just don't close off so many ducts that you can't get the minimum required total airflow. If you don't have enough ducts, you need to add more or larger duct upstairs.

I was going to install a second separate system for my upstairs (that is certainly the best design). But I've been impressed with the new variable speed single system I just had installed and it definitely blows more air upstairs compared to my old oil furnace. I can also close off up to 3 downstairs vents and still have a decent static pressure loading on the fan. But some of the open downstairs vents are getting noisy by this point because they are flowing so much air.

[big al2]

Have seen that situation many times. The problem has to do with access to the duct buried in the walls and floor.

Anything can be fixed, but how much will it cost?