Return air for a 5 ton air conditioner unit?

Question

I am installing a 5 ton A/C Heating Unit

What I have for return air is
Three - 6" Circles & One - 8" Circle

(I am using my existing floor vents for return and adding ceiling vents for cooling & heating) (I had return from ceiling but I changed the return air to the floor)

Will this be enough or could someone tell me how to figure out if it is enough????

Please help

I was told that an 18"x18" grill was enough return air and so 6+6+6+8=26" right?????? HELP

" is inches right???

Thanks, confussed wife

What I had was a down draft 3 ton unit. we added the 6 and 8 inche circles with tees to provide air to other rooms in our home.

Then years later we have decieded to get a bigger unit, Up Draft.

We then added air vent to all ceilings in all rooms.

We have hard wood floors, so we are going to just use the old vents as return air and need to know if we need more return air vents??

We have about 10 vents in the floor throughout our house that that turn into the 4 I mentioned above (three 6" & one 8" circles) that will then go into the new unit at the return air site.

Answer 1

Are you and your husband doing this yourself? If not...the contractor that sold you the new 5 ton unit, should of matched what you already had in the house. (ductwork & inside hardware) If not, and you are doing this all on your own, then...most of this has already been answered before I came along. Take the advice of the guys before me on doing a 18x18 return grill and calculate your square footage and tonage, to how many vents you need and where? Towards the windows( to fight heat) and depending on the sizes and heights of the rooms tells you how many vents per room, and also the air flow.....it's pretty complicated stuff if you don't know what your doing? Good Luck w/it! I hope it works out for you!

Answer 2

To determine the proper size central air conditoner a whole house "HEAT/COOLING analysis should be done. That takes into consideration the following: Direction the house is facing (N, S, E, W), the R-Value of the insulaiton in the walls and ceiling, the types of doors and windows, the square footage of interior, Number of doors and direction each faces, type of window coverings (blinds, drapes) and the number of occupants. The sum of all the numbers will give you the number of btu's needed to cool your house on a 95 degree day. By dividing the number of btu's by 12,000 you will then have the exact tonnage necessary.
Some people will only use total square footage of the house to arrive at a figure. That is not accurate but done often by those who do not either know how to do a cooling analysis or are lazy.
If you oversize a central air conditioner it will not cool yur house properly. It will 'short cycle'....i.e. run for a short period of time and shut off, gthereby not remove all the humidity and leave your place uncomfortable. If you UNDERSIZE the unit it will run and run and run. That may not cool the house and only run up yur electrical bill.
The very old rule of thumb (not used anymore) was that you need 4 supplies and 1 return for each TON of air. Example a 3 Ton unit would need about 12 supplies and 3 returns.
Return airs mounted high on the walls or in the ceiling are better than floor returns. Remember that heat rises, so why have supplies in the ceiling.
By adding ceiling fans a central air unit seems to run more efficient and cool better.
Who told you that you needed a 5 Ton unit. That is veryl large and expensive to buy.
I have a 2900 sq foot house, a 3 1/2 ton 14 Seer unit with 12 supplies and 2 returns on the first floor and 10 supplies and 3 returns on the second floor. The results of the heat/cooling analysis said I needed 38,500 btu's so I went with a 3 1/2 Ton unit.
Ask your contractor to provide you with written warranties that what he is recommending will cool your house to YOUR SATISFACTION and that the warranties are a minimum of 10 years on the compressor.
The brand of the equipment is important also. If you need more data, email me.
I hope this helps and is not confusing

Answer 3

The larger air handler on the inside was an attempt to increase the cooling capacity of the unit. That may or may not have made any difference but it was a cheap way to go. If you have a hot spot in the house that could be a reason for the extra duct and return - to balance the system better. A 3 ton unit should be sufficient for 1500 square feet unless there is no shade and more than the usual amount of windows (like a sunroom). BTW putting in a larger unit may have the opposite effect as one of the objects for AC is to dehumidify, which requires the unit running a certain amount. A too large unit will not run enough to perform that function.

Answer 4

no the 6 and 8 inch pipes give you about 125 square inches. the 18 x 18 grill would give you about two hundred in free air area depending on the manufacturer. apparently this is in the design mode and not in a actuality. and the AC must be a self contained unit. If it is a split system the furnace air handling system should be sufficient to use as it is.

Answer 5

I need more info to steer you right. Was your previous unit 5 ton? Why are you changing duct work in the first place? In a perfect world you would have a high and low supply and a high and low return for total of four registers per room. For combined heat and air you should have a high (ceiling) and low (floor) return on each floor. If you're to put 5 tons on 3.5 tons of duct you're going to have trouble. RScott

Answer 6

No what you have is not equal to the recommended 18X18 grill. 18*18=324 sq inch, Area of round duct = pi*r^2
for 6 inch:3*3*3.14=28.3 times three ducts = 28.3*3= 84.8
for 8 inch 4*4*3.14=50.26, total 50+85=135 sq. inch.
This is only about 1/2 of what you need.

Answer 7

first why are you installing a five ton unit....after doing a heat calucation you will find it equals to one ton for every 750 sq ft .unless you have a lot of windows or glass doors facing southwest.then you would reduce this to 700 sq ft per ton.......so if you have a 3000 sq ft house you would only need four tons of air conditioning. or four and a half if you have a lot of southwesterly facing windows and glass doors....you measure duct work by sq ft ...so you would only have half of what you need ..for round duct you figure sq ft by multiplying the radius or half of the diameter squared times pi. this will give you square feet..then add all of the sq ft from each duct for total sq ft..if you dont need 5 tons get a smaller unit

Answer 8

The first answer is correct. You have approximately half of what you need. Designed at .05 static for the return at 2,000 cfm is 18*18 free opening for return air.

Good luck!
Newt.