5 ton unit on 4 ton ductwork?

[stvokc]

5 ton unit on 4 ton ductwork? Duct work is sized for a 4 ton but Icontractor wants to put in a 5 ton condensor & evaporate coil unit to cool the house better. House is 2750 sq ft. The contractor thinks I really need a 5 ton unit instead of a 4 ton. The problem is that all the duct work is in the concrete slab and can't be expanded. I realize that the cfm for a 5 ton should be 2000. The cfm on the old duct work is 1600.

Will the 5 ton perform well in a 1600 cfm duct work system? Or will it NOT perform well in a 1600 cfm ductwork?

The return suppy is currently sized at 1950 cfm. It can be increased because it is in the attic.

[desert tech]

If the contractor feels that a 5 ton is what you need, and he feels that your ducting is adequate, then get a second or third opinion. If you are going to spend $ on your residence, and this is not chump change you owe it to yourself to get other opinions. just remember that the people giving you bids are salesmen not techs. call around untill you find the right person that makes you feel confident in them doing the work. Should be no less than 18 inch opening on return side ductwork. I do believe that your return air runs in the concrete. thats how it is in az. . where is the air handler located?

[wormy]

Did the contractor perform a load calculation?
Or did you comment to him that "my old unit ran all the time" and he said "Oh... we can fix that by putting in a bigger unit"?

If he's going by your comment... then he'll make more money from you by selling you a bigger unit and you will be happier under the 'false' impression that "BIGGER IS BETTER"

Did you add on to the house and add more heat load since it was built?

Setting aside the units run time.... did the old unit keep you comfortable? (you may have to think back to when it was first put in... neglect and poor maintenance will have a serious impact on how you feel during the later years of the units life) If it was comfortable back then... then a new 4 ton should be comfortable now.

Not sure where you live, but check with your local power distributor to see if the have a program like this one in Tennessee... http://www.energyright.com/heatpump/index.htm
Very nice program in my opinion.
They've set excellent standards on installation, have a list of qualified contractors you can get estimates from, they come out and inspect the work to verify correct air volume and heating/cooling capacity. They even require you get a 10 year parts and labor warranty. So your good to go for years to come.

[wormy]

oh yeah... consider a variable speed blower also.

[stvokc]

The old 4 ton did not really keep the house cool. That is one reason why the contract is saying go with the 5 ton unit.

The house is 45 years old, 2750 sq ft in hot, humid Oklahoma. Contractor said I should really have a 5 ton to cool this house good. But all the supply ducts are in concrete floor. The cold air return is in the attic.

The contractor said that the supply ducts is 1600 cfm and that a 5 ton unit should have 2000 cfm. He said that it should work fine to put in the 5 ton since we cannot add any more supply ducts since they are in the concrete. The cold air return in the attic is already 1950 cfm.

Will a 5ton unit work good on this set up? and cool the house better then a 4 ton set up?

[stvokc]

Contractor is going to put a TXV valve installed to help regulate wide outdoor temperature swings anyways. If coil freezing might be an issue then the TXV valve should help keep the coil from freezing if that is an issues about a 5 ton on a 1600 cfm duct work.

[Freezeking2000]

Just because the duct work is sized forr 1600 cfm does not mean that it will not supply 2000 cfm. What it means is higher velocity and a little more noise. The static pressure will rise in the ducts. I personally do not believe you will have a problem.

Was your old system running constantly all day on warm days and not reaching setpoint?

If you were comming home and turning it down that is not the way cooling is sized. You are better off from an energy standpoint to keep the 4 ton and have it have very long run cycles that a 5 ton cycling. My cooling unit cycles on and off until 12pm then does not shut down until 8 pm when 90 degrees or more which was its design temp.

I would increase the seer rating to at least 14 seer and stay with a 4 ton, most likely the currect 4 ton unit has dirty coils and blower which is contributing to your lack of capacity. How did the 4 ton unit work when new and how old is it?

[captainrat]

what brand / seer is he selling you ?

[stvokc]

Old coil is spotless as I have the unit serviced every year to keep it running the best it can since not cooling house like house should be cooled.

Old 4 ton would run all the time and not be really cool enough in the house. Would think 5 ton would cool the house to be confortable.

Rooms are large and could use more force coming out the register to stir the air in the rooms. I would not mind that.

[hvac64]

Maybe you could go with a 5 ton ,2-speed unit and var. speed a/h, will run at 1/2 capacity lots of days for better moisture removal. Costs more, but worth it!

[tinknocker service tech]

i am not sure i read right first 5 tom condenser ok now if it is a 5 ton coil only and not furnace and the furnace is rated at 4 ton air flo 1600 cfm you will not gaina thing with out changeing the furnace to with a 5 ton drive
if it is a 5 ton fan coil airhandler then you are fine
since your duct work cant be changed than you should concider haveing a varitabale speed blower installed it comes with furnaces and airhandlers most manufactors have them. some will not agree but they were made for this problem and they also increase the the seer rateing to
this blower will ramp up to 2000 plus cfms depending on how the control board is set up. this blower will over cum the stadic pressure in the duct work and give you a true 2000 cfm see your dealer and ask about if or go on line i am sure you can fined out more check under davelenox,com or trane. or carrier they will show you just how it works and you wont have to worrie about you ducts or cfms

[stvokc]

Furnance will be new 125k. New condensor & coil will be 5 ton. Everything new except duct work. Existing duct work is in concrete floor and is sized 1600 cfm for a 4 ton unit.

Current condensor & coil is 4 ton. House has always had problem cooling enough. House is 2,750 sq ft in hot Oklahoma with all brick and large large windows. Also furnace is on one side of house and master on the opposite side with around 60 -70 feet of duct to get to it. With faster blower setting for 5 ton he said would get more air flow in that long run to master.

Contractor says the house really needs a 5 ton unit to cool the house better for this size house. 4 ton has not really cut it in the past 15 years.

My question is will the new complete 5 ton unit work OK in the old, 1600 cfm duct work system? Or should I have the contractor install a 4ton complete air unit?

[rockdean]

How do you know you have 1600 cfm of air in your ducting? Unless you run a test you wont know if your ducting will handle 2000cfm of air flow. Do you need a 6 ton system? Who knows ,no one could with out a load calc. Good luck

[AllTemp]

If the 4 ton system never kept up and cooled all these years why the sudden urge to upgrade ?

The difference ebwteen a 4 ton and 5 ton isn't goign to make alot of diference to you if the probelm is in inflitration of that hot Oklahoma temperture...

Invest in some good insulationa nd look into better windows and sealing that house up...

As a contractor I sure wouldn't stick my neck out on a 5 ton if the 4 ton was less than marginal... Yopu've got some other issues goign onthere that need to be corrected first and foremost...

I think the options of a VS air hadnler or FAU is great it will help over come any static pressures issues. But until you have the issues corected, isntallign a 2 speed system such as the Infinity System you'll find your self with some dissatisfaction guaranteed....

Have your house carefully evalulated for it's heat loss and gains, you be glad. Especially if you figure out where all this coolness is going...

[Edited by AllTemp on 03-14-2005 at 02:34 AM]

[stvokc]

House has R30 attic insulation, HVAC units are spotless, freon levels correct (I have unit serviced every year to get best performance out of them), attic power vented.

Contractor ran heat load calculations/test and says that this 2,750 sq. ft house should have a 5 ton AC and a 125,000 furnace. Contractor says that he calculated that the current duct work will handle 1600 cfm which is correct cfm for a 4 ton AC system. He said that the new 5 ton AC system calls for 1,800 cfm (talked to him this morning). He said that the 5 ton will work fine on the 1,600 cfm ductwork system with just a little increase static pressure.

Plus would get a little bit more force of air (because have to turn up the speed of the blower to handle 5 ton AC instead of 4 ton speed) in the duct work so would get more air pressure to the far, 60-70 ft. run to the master bedroom.

Is what my contractor telling me correct?

Going to replace whole HVAC as the units are around 25 years old. I am hedging my bet that they will break for good soon. I would rather deal with replacement of all HVAC when it is an emergency to replace. I would rather replace everything at once and get a matched complete system that is more energy efficient.

[dash]

Could be the 4 ton didn't cool well ,due to undersized ducts.

Sounds like your guy has checked the duct system,and knows it will be okay.We can tell fromm here,without a lot more info.,and we still wouldn't know for sure.

Did they check the External Static of the current system?If so what was it?

Return ducts can be increased ,this will decrease the ESP,and allow more air flow.
350cfm per ton of cooling(1750) is the max. you want in a humid climate.

Supply grilles can often be changed to increase air flow.

Go with a variable speed indoor fan,for sure,check out an Infinity Control System,by Carrier.

[tinknocker service tech]

to start off sorry for the spelling. i can spell just cant type new to the pc and typing sucks hehe. now that you have the info you need from your contractorwe have something to go on. i deal with lenox mostly for 14 years now so i will use lenox for example onlt doesnt mean it is better. i was talking to my lenox tech rep about nate and other thing so i ran by him this problem and here is some facts for you. with a variable speed blower in your system you can set it to ramp up to full speed +10% it will give you a total of 2250 cfm in the duct work. this motor will overcome the static presure of under sized duct work. even if your ducts were sized at 1600cfm this blower will still ramp up enough to give a true cfm it is told to give. since you are concerned about the size of your ducts and air flo a variable speed blower will solve your conserns. carier, trane, york, goodman, all carry it.
the variable speed blower solve a lot of problems air flo is only one. another is himiditi is is another. with lenos you can use a two stage condenser where the compressor has two speeds high speed 5 ton and low 3.2 tons system reaches set point say 74 degrees the blower will ramp down and condenser will go to high stage pulling humiditi out with out cooling. when reachs humiditi set point will go to low stage on condenser and ramp up blower to maintain cooling. will need a humidistat also. now trane and carrier have the same setup also and works well only lenox two stage will not give you a seer rateing higher then 11 seer. only draw back to it.

[dash]

There are limits to what a VS fan can do,especially when you get in the 5 ton range.

Most can't deliver 2000 cfm above .4 ESP ,now 1750 cfm can be delivered up to .7 or .8 ESP.

[beenthere]

What Dash said.

Plus, you might not like the noise from that supposed 1600 cfm duct, if you put 2200 through it.

[AllTemp]

Am I the only one picking up tht this morning his contractor told him he neded 1800 CFM for 5 tons....

YOU NEED 2000 ...