Second Floor Is Too Hot to Sleep in Summer

mdfaccMarch 24, 2010

My sibling has a standard 4 bedroom, 2.5 bath, 17 year-old 2-story home with a first floor master bedroom. The foyer and great room have 2-story ceilings.

The second floor bedrooms are so hot and uncomfortable at night that my sibling had to place a window A/C unit in the one that is occupied. (The home has central A/C and the first floor is always comfortable.)

What can he do to diagnose and fix this problem? Could it be that he needs an attic fan, or better insulation in the attic? (The attic is not livable space.) Is there a solution without a dual HVAC system?

Thanks for any help.

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Unfortunately, his is a common problem. A lot of homes in extreme locations (i.e. cold winters, humid summers) - while designed with duct systems adequate for comfortable heating (I don't know your location) lack the duct capacity for the cfm and velocity required for cooling. Often, and in any location dealing with high outdoor temps, if upper floor cooling wasn't specifically taken into consideration in the systme design it is difficult if not impossible to introduce enough air through the existing duct system.
Something to try - if they are accessable and balancing dampers in the supply lines or registers exist, is to turn the lower floor area supply pipes down in an attempt to force more air to the upper floor. The system may run longer to achieve the same results at the lower level but may improve the upper, and that's what you're after.
You indicated high ceilings in the great room and foyer. Chances are, if you could put on your wings and hover above, while it may be comfortable in the occupied "comfort" zone below, it would be uncomfortably hot up there as well. Most of that is cuased from solar gain. (heat absorbed by the roof deck and/or attic area) If there is inadequate insulation, the heat absorbed by the roof or concentrated in the attic via the roof will radiate through the ceiling. Poorly insulated walls will add to it as well at different times of the day and by that same principal of radiation.
If there are sufficient ducted supply air outlets in the second floor and there seems to be a good velocity in terms of air flow, another problem may be inadequate return air intakes. You can easily check this by taking notice as to whether the situation seems to improve when the doors are left open in the upper rooms. There's a chance that pass through relief registers can help if that's the case - with the idea that when a room becomes pressurized no more air can enter than can escape. Comfort depends on good air exchange. It might help some, but rarely is the fix so easy.
Window air conditioners are noisy and irritating as you probably well know. But there are split system units available that place the condensing unit (the noisy part) outside on a ground location and the evaporator section (actual cool air delivery part) in the room. Most models over time have improved a great deal and have reached a point where the indoor unit is extremely, almost unbelievably quiet and, in appearance, pretty inconspicuous. Refrigerant, low voltage wiring and condensate lines from the outdoor unit to the indoor do have to be dealt with. They can be run inside the wall, but it is most often easier and less labor intensive to run them outside. There are cover mouldings available in a variety of colors to lessen the mechanical appearance of the lines, and done well, really don't look all that bad.
More than one indoor evaporator can be connected to a single outdoor condenser with the choice of the right equipment. Most indoor units are wireless remote control and ideal for problem areas. Theese systems can be a bit pricey, but have come down considerably over the years.
So check his register locations, return air intakes and attic/roof/wall insulation. Additionally, but probably not something most people want to consider for asthetics sake - light colored roofs can be a big help as they are more reflective.
Long winded! But I hope it gives you some ideas!
Thanks for the chance to blab!

    Bookmark   March 25, 2010 at 1:49AM
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There are a couple of very simple (and cheap) things you can try to improve this situation:

First, try to figure out how the air is moving throughout the house. Given that hot air rises and cool air sinks, is the natural flow of air in the house helping or hurting comfort. One of my siblings had the exact same problem, by studying the air movement we learned that two of the three supply registers in the hottest bedroom were blocked by furniture. Further, most of the air was short-circuiting back to the cold air returns on the bottom floor.

The second thing that is effective on marginal systems is to run the air handler (fan) all the time. Many modern systems have an air-reduction mode that reduces the speed of the AH when the unit is not calling for heating or cooling. This keeps the air circulating, filter filtering, and is the least expensive part of the system to operate. The fan costs pennies a day to run all the time and may improve comfort levels in the house.

The most important principle to remember is that hot air rises and cool air sinks--use this to trouble shoot the system. The second most important principle is that air flowing toward a human makes us "feel" cooler than air flowing away from us. This is why ceiling fans have summer (air flows down toward the living space) and winter (air flows up away from the living space) settings.

Hope this helps,


    Bookmark   April 4, 2010 at 2:31PM
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I am having the same difficulty. Recently saw an article in the august family hadyman magazine that discussed level-to-level ventilators as an option. They pull air from the first floor to the second, hopefully balancing temperatures. Has anyone used these. they sound too simple...

    Bookmark   June 25, 2010 at 12:06PM
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NO attic fan. They are generally a bad idea. Increase attic ventilation by other means if what you have is not sufficient. Install a radiant barrier in the attic. More insulation might help if you don't have enough. Probably more important is stopping air infiltration from outside. Check ducts for leaks. Where do the ducts run?

Approaches may very depending on your climate, humid or dry? Where does sib live?

    Bookmark   June 25, 2010 at 7:36PM
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Maybe buy an extra fan?

    Bookmark   June 26, 2010 at 10:26AM
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You said the home was 17 years old. Is the A/C unit 17 years old? The reason I ask is that my home is 37 years old and had the original Bryant oil furnace and a 24 year-old A/C unit here in Maryland. I recently replaced all of the HVAC equipment with an oil furnace and a Heat Pump.

For the past twenty years the upstairs was always too warm during the summer and nothing I did corrected the situation. In that there is just my wife and I, we installed a window A/C unit in our MBR and survived that way.

We had both the A/C unit and furnace serviced annually and I maintained the filters clean. In fact, I replaced all of the equipment as a preemptive strike rather than have something fail and me finding myself in panic replacement mode.

The replacement heat pump is 3 ton just like the old A/C unit, but it is a two-stage unit and it has a variable speed inside fan - all Carrier Equipment.

With essentially no change to the ducting (we did add a return in the basement to address a high humidity concern) the upstairs now is plenty cool and the Heat Pump easily maintains whatever temperature I set the thermostat to.

I'm not sure I fully understand why my home's comfort level has improved so much with the new installation, but I'm thinking that the air-flow thru the ducts is much greater then with the old A/C.

    Bookmark   June 26, 2010 at 10:55AM
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Ionized: The house is in southwest Ohio.

Saltidawg: The HVAC for the house was replaced last year.

    Bookmark   June 26, 2010 at 1:11PM
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I am not familiar with the climate in SW Ohio. More insulation in the attic might help a lot. It depends on how good the insulation is that is already there. A radiant barrier might help too. HOw is the roof? An efficient white metal roof is a costly investment, but will last a long time and cut energy costs. Fixing the ducts might help a lot too.

How tight is the house as far as air infiltration? The ducts might be leaking a lot of your AC output to the outdoors and forcing the system to suck in outside air to replace it. When I write "ducts" include the return(s) in that,

Check for dampers as advised above. You really need to look at the whole system (house).

    Bookmark   June 28, 2010 at 6:55PM
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