Home Comfort

S Ebels

There is a ray of hope however, if the HO will go for installing sufficient return area at the floor level. The key word here is "sufficient"! I'm guessing that the A/C installed is a minimum of 3.5T capacity, maybe four. If you use the correct static pressure on your return you would have to open up a minimum of 3 stud bays per ton, 4 would be preferable. That's figuring a free area of 3.5 x 14" in each opening. So given those parameters you'd need 11 to 13 return openings. Good luck with that!

Others have mentioned ceiling fans and constant on fan and they will help, especially a variable speed type blower on the furnace. (This would be the only reason to swap furnaces as far as I can see) All that being said, your customer will never be truly comfortable with that system. I'd explain the possible band-aid approaches to him and then recommend a panel rad system to him. Running tube around the house won't destroy any more of his walls than the other "fix".

Heating systems like his should be banned along with the hacks that put them in. There's ALWAYS a better way than what this poor soul has been cursed with.

[Deleted User]

Home Comfort

I just had a customer (new) call our office and here is his problem. His house is built on a slab with about 2200 square feet of heated space. Both gas furnaces and A/C are in the attic. He has 10' ceiling and says the air never reaches the lower level. All vents both supply and return are in ceiling. One contractor has tried to sell him a larger unit another has told him to block off some of the return vents. I have not laid eyes on this house but will go out this week and wanted to get some input from the experts before I do so.

JOHN_103

try to get some returns down low in the wall to get cold air off the floor.

Mike T., Swampeast MO

While such an arrangement is good for cooling, it's THE WORST for heating. There's VERY good reason that 8' max. ceiling height is typically used in such systems--still not ideal, but tolerable.

Where impractial/impossible/too expensive to relocate at least the returns (as recommended), ceiling fans will help considerably.

So-called "hi-low" dual returns (you shut off the high returns in the winter and the lo in the summer) are a comfortable, if rather expensive, addition to ANY combined forced air heating/cooling system.

GMcD

Let me guess

The slab on grade isn't insulated, nor is the perimeter of it. Probabaly standard stick frame construction with batt insulation in the wall. Think about it- warm air rises, so blowing warm air down from a ceiling requires a lot of fan power as well as really good supply air register design/selection to get the required face velocity to blow the warm air down so it mixes with the room air, and without making any noise. Good luck with that.

I also suspect the mean radiant temperatures of the slab and wall surfaces are cooler than 65F, which means you'd need an average ambient air temperature in the room of at least 78F to hit the magic comfort feeling.

Brad White_55

Another version of Crank it Down...

Newton's Fourth Law: Gravity Wins.

One of the conundra of heating when doing so from above is the tendency to fight bouyancy with hotter air. Sort of like giving a drowning man a glass of water and instructions on how to gargle...

To sell a larger unit and block off returns? Mmmmmm.

Whenever I design a system that has to heat from above, first off (after I have exhausted all other avenues), I specify the lowest supply temperature that I can, rarely over the 100-110 degree range on a design day. This means of course, more air because of the lower delta-T. If you can increase airflow to reduce delta-T that may help. But if you are still in the 120+ degree range, low returns are the best bet hard as that may be to swallow.

The suggestions of low returns are the only practical solution, what goes in high comes out low and vice versa. In mild climates with modest heat losses and predominance of cooling you may get by, but if the heating and cooling approach parity, you have to design for the worst aspects of both (assuming you are sticking with FHA of course).

I agree in principle with Mike T.; use a seasonal high/low arrangement or to keep it simple, supply high and return low year-round. No harm in that. So basically I concur with what has been offered thus far.

Terry_14

Mild success

I have had mild success corecting this problem. I found locations that allowed ducts to be hidden in closets and pantries. I would opt for heat runs rather than returns at floor level. For summer A/C use Trolatemp dampers would close off new heat runs and allow cooling from above only.

When you correct the problem PLEASE post results allowing us all to gain insight

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Terry

Derek Moore

hot air high ceilings

sounds like the wrong approach, I would bet the ceiling is 90 degrees. an inexpensive thing to do is put some paddle fans on the ceiling "blowing Up" or in other words "reversed" they will push the heat sideways and down. System would have been better as an AC system with a radiant floor.

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John T_3

Constant low speed fan

I have had good success using transfer fans of some type to mix the air ceiling to floor. I think it best to remove cool air from the floor and mix it with warmer air at the ceiling level. This way you get away from air blowing right on occupants which will result in a cooling affect.

Install low wall returns, you may not need all the returns low but make sure you can balance the returns to assure air flow into the low wall returns.

Replace the forced air equipment with variable speed drives that will allow constant low speed fan operation. Again verify airflow thru low wall returns.

You could also install a Hepa style stand alone filter(s) with new low wall returns and high wall supply. Set the unit(s) to run continuously, this would give you air mixing and cleaner air. These units can be found with efficient fan motors and are usually very quiet.

IMHO, low wall returns (or supply) will not be affective without constant air circulation.

John T.
Custom Climate Systems, Inc.
Dexter, Michigan

Brad White_55

Excellent point, John

Constant circulation rules in most cases, especially with limited low return locations. The VFD approach has merit for long-hours energy savings but does have to be weighed against outlet temperature rise going too high. Then you are back where you started, possibly bouncing off high limit. I imagine some condensing furnaces with modulation may have a shot...

John T_3

Vairable Drives

can be set-up with continuous, low fan speed whenever there is not a call for heat. It then ramps up when either the first or second stage of heating is called on. Regardless getting the cold air off the floor and bringing the heat down to occupied zone will usually alleviate the comfort issues.

I had a system like this in the first office space I leased. All I did was use a small transfer fan and did nothing with the ceiling supply and return diffusers, the difference was night and day.

John T.
Custom Climate Systems, Inc.
Dexter, Michigan

Techman

home comfort

good evening.Installing combo hi/low returns will give you good overall comfort along with continuous air flow in the colder outdoor air temps .SIZING YOUR RETURNS AT .06-.08 INCHES OF WATER COLOUME.That gives you about 150 CFM for each wall bay at the 16" on center rule . A typical problem is the closing of interior doors [ bedrooms,bathrooms, unused rooms]so having returns in several rooms plus the "main return" will make for a better system.Good luck.This A.C. system has to be about 4 tons or 2000 CFM.

Brad White_9

That makes sense, John

I remember a mentor describing the electric swizzle stick; how a small fan blowing continuously could excite every molecule in the Houston Astrodome. Sooner or later every molecule of air would pass through it.

In the practical side, we do specify a lot of fan powered series flow constant volume boxes in commercial/institutional work for similar benefit. Of course with hot water heating coils that is less problematic; great to see the FAH industry allowing that kind of control. Thanks for sharing!

Brad

EBEBRATT-Ed

The first 4 posts nailed this thing shut. Overhead heat is just bad especially with 10' ceilings. Lower returns and a properly sized unit are the answer.

Ed