To start, I'm 100% not technical or mechanically inclined (you'll learn quickly when you read this).

I have a 2 story house with finished basement and beating my head against the wall figuring out, if anything, that I can do to keep the top floor cool without making the main floor and basement a freezer. I know this is a typical issue with 2 story houses but the temp varience between main and top floor is 5-10 degrees difference in the heat of the day.

I live in Denver, CO which means it gets hot in the day during the summer (80-low 90's) but cools off at night (50s-low 60s) but the afternoon and early evening kill me... bedroom and home office where I work are upstairs all day.

When we bought the house the inspector told us the AC unit was a bit too small for the house size.. dont remember the AC size but house is 2100 up and main floor (3100 w/ basement).

Big question (understand I'm clueless on this stuff)
-Is the poor cooling upstairs 100% attributed to the fact the unit is too small?

-Is there anything that can be done besides replacing the AC unit?

-Is it possible to improve the cold air return or whatever it is that circulates air from one room to another?

-Is an attic fan worth it? I've heard the electrical power it consumes and/or fire hazard some people believe indicates it may not be worth the investment.

-Is bringing an HVAC person out for an evaluation a good idea or is this just the nature of the beast?

-What info would I need to gather to provide someone to help make recommendations?

Any help is greatly appreciated!

You could install a ceiling fan downstairs the fan direction is reversible, spins both ways, to pull warm air down the stairs where it mixes with the cooler air. Or shut some registers on the ground floor to even out the temp

Thanks wildandblue!

Would shutting registers increase cool air to the top floor or just not cool the main floor as much?

Also, we shut registers (2-3 in the basement) last year and froze up our unit twice. Is there any specific approach that might work better than others, i.e. shut a couple registers on main floor furthest from the AC unit?

Attic fans, additional insulation in the attic, more attic vents... all are good ideas. If you can keep the attic cooler, you reduce the air conditioning load considerably. Have your HVAC unit checked by a reputable service company, get references if you aren't sure. Talk to neighbors about their cooling issues. Sometimes keeping the blower running constantly will help de-stratify the space. Does the thermostat keep the area it is located in at the temperature you set it? And do you have 2 levels or three... is it top, main and basement?

If you can close off the second level, this will keep more of the cool air from settling down to the lower floors and help prevent all the hot air from rising to the second level.

Some fans, upstairs to keep the air circulating, would help as well.

If the unit is too small, that is the biggest issue, and while expensive to replace, may be necessary to achieve the temp you desire.

Thanks all again!

Missouri bound-
- we do have a reputable HVAC company I can call... probably should be 1st thing to do
- it is a 3 level house, basement, main floor and top floor (didn't know basement was counted)
-thermostat does keep area (main floor) at the correct temp

Progunr
-not sure what you mean "close off second level"... close vents on main floor? Top floor?

Did we close too many vents when we froze up the AC unit last year? Should we try it again?

Thanks evreyone for the help and advise!

Sounds like you need to look at keeping the attic space cooler by ventilation, or isolating the attic from the upper level with better / more insulation. If the air conditioning is keeping the house at the temperature you set it, other means need to be looked at. But still start with a good hvac company.
Good luck and keep us posted.

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Originally Posted by b5280high

thanks all again!

Missouri bound-
- we do have a reputable HVAC company I can call...probably should be 1st thing to do
- it is a 3 level house, basement, main floor and top floor (didn't know basement was counted)
-thermostat does keep area (main floor) at the correct temp

Progunr
-not sure what you mean "close off second level"...close vents on main floor? top floor?

Did we close too many vents when we froze up the AC unit last year? Should we try it again?

Thanks evreyone for the help and advise!

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I was speaking to actually closing, as in a door, or hanging a heavy blanket, so that there is no large open space leading up to the second level.

Is the basement an air-conditioned space? Is the furnace in the basement?
What is the size of your hvac unit, BTU and tonnage, should be listed somewhere on the furnace. And if the basement is not air conditioned, it shouldn't be part of the calculation for heating / cooling requirements.

I would suggest rigging up a small fan in your bedroom that goes into your vent and sucks the cold air up into the room. This worked for me very well.

Ceiling fans increase circulation and therefore decrease the strain on your HVAC system, several properly placed ceiling fans can deffinitely help counter an AC unit that is too small.

If there is a large open area between floors such as a foyer or stairwell, a ceiling fan installed there can help equalize temperature between floors.

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Big question (understand I'm clueless on this stuff)
-Is the poor cooling upstairs 100% attributed to the fact the unit is too small?

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Not necessarily. Cold air sinks. Hot air rises.

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-Is there anything that can be done besides replacing the AC unit?

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Turn off the registers that blow air downstairs. Have a bypass damper installed (used for zoning) so motor isn't strained.

Zoning could be installed. The damper is recommended in either case.

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-Is it possible to improve the cold air return or whatever it is that circulates air from one room to another?

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What is supposed to happen is warm air from the rooms is supposed to be drawn into the furnace in cool mode and vice versa in heat. This is accomplished by the ability to turn on and off return grills located near the floor and ceiling.

Most returns upstairs should be open. The downstairs ones closed.

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-Is an attic fan worth it? I've heard the electrical power it consumes and/or fire hazard some people believe indicates it may not be worth the investment.

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They are relatively inexpensive. They are thermostically controlled. They are worth it.

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-Is bringing an HVAC person out for an evaluation a good idea or is this just the nature of the beast?


-What info would I need to gather to provide someone to help make recommendations?

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Pay someone to do a manual D (duct design) and Manual J (sizing) and make a reccommendation. Allow you to keep the results. This will tell you if there are inefficiencies with the ducts or size.

More often than not there is a recommendation of two units. One for up and one for down.

We can't see. But a ceiling fan that pushed up on the stairwll might help.

Guess:
Design some sort of balancing scheme. Install a bypass damper, do something in the stairwell. For heat you may have to do something different. Improve the return system.

What is a bypass damper:
The blower in the furnace has to move air. Think of what happens when you clog a vacuum cleaner hose. The sound changes and the motor heats up when the opening changes. A bypass damper is pressure sensitive passage around the blower such that the motor never sees the change in air flow. Not required on very few designs. Namely Carrier products.

Zoneing:
Two or more thermostats control register or duct dampers automatically.

Any help is greatly appreciated!

b5280: Stated the following,

Also, we shut registers (2-3 in the basement) last year and froze up our unit twice. Is there any specific approach that might work better than others, i.e. shut a couple registers on main floor furthest from the AC unit?

I am wondering if the fan output is sufficient (moving enough volume through ducts.
3 vents closed should not cause "Freeze Up".

Slimton:

The way the system is designed is for a particular air flow. When you restrict the airflow (closing vents), the system has to be smart and it will try to protect the motor. The motor slows down and iceing is possible.

The bypass damper will FIX that problem. You could close all the registers and the system would be happy.

Also if your not truly returning hot air from the ceiling level, the coil will be colder. You need a set of returns, one at ceiling level and one at floor that can be turned off. You flip which one is on depending on he season.

Thanks again to all, you're coming up with some great ideas!

Celing fans- I have 2 ceiling fans, one upstairs in the bedroom and one on the main floor in the family room. I'll reverse the fan upstairs to bring in cooler air... good call!

Bypass damper- I DO have a Carrier unit, Model 38ckc042... 3.5 ton cooling a 3,100 SQ foot house (2,100 SQ upstairs/main floor, 1,000 basement). KeepItSimpleStupid, given this is a Carrier, does a bypass damper still make sense?? I love the idea if it makes sense

Warm/cool air returns- I have a warm air return right outside the bedroom (top floor) and 2 cold air returns on the main floor. Does this change any recommendations?

Attic fan- Sounds like a an affordable option... If moving cool air up is difficult, moving hot air OUT sounds like an easy way to help.

Does the above sound logical?

Your returns are All messed up. There should be returns in nearly every room except:

Bathrooms: Too much moisture
Kitchen: Odors
Utility room: products of cumbusion

You may not have enough return air and they are all in the wrong place. If you have cold air (located near the floor) returns on the bottom floor, it's just going to make the bottom floor colder. Think what an AC does. It lowers the incoming air temp by 15-20 degrees.
If you keep pulling in 75 deg air, you will lower it to 60 deg. That's why the bottom floor is always cold.

You didn't say where the t-stat is located?

I'd like the model of the heater/air handler. I'd also like to know what t-sat you have. Particularly if you have Carrier's infinity control.

You have big return air problems.

I missed a couple returns in earlier post...
Basement
-Cold return just outside of furnace room
Main floor
-Cold return in kitchen island (middle of kitchen)
-Cold AND warm return in hall just outside of kitchen
-Cold return in family room (right by kitchen and hall w/ other returns)
All returns on main floor (listed above) are within 15 feet of each other... seems odd
Upstairs
-Warm return in hall outside of bedroom

T-Stat on main floor is 5 feet from warm and cold return in hall just outside of kitchen
T-Stat model, Carrier AC01-B
Heater, Carrier 58PAV- don't know which unit size (can't find on the unit)

One thing I forgot to say in earlier posts, when the house was inspected when we bought, 10/05, house was 6 yrs old at the time, the variance that was tested was 25 degrees, normal range was listed by inspector as 15-25 degrees.

Here is some brief info on bypass dampers. The Zone Control Blog: Barometric Bypass damper

You might be able to benefit by installing one. With it, you can close any amount of registers that you like.

Shutting off some of the return air and even the registers. Problem is you can't do that without the bypass damper AND the ability to turn off the returns, otherwise the coil can freeze up.

I'm thinking, turning off all/most the registers on the first floor and all/most of the returns.
Cool air would be discharged upstairs and gravitate downstairs.