What size unit? - Page 2 - Contractor Talk - Professional Construction and Remodeling Forum

Texahoma · 03-11-2009, 09:54 PM

Just curious did any of these contractors provide you with a load calculation? Did they take the time to measure your rooms, windows, doors, check the building materials or makeup of your house? Also what about ductwork? Are they going to throw a 5 ton unit on 3 tons of ductwork? If so your heading for more trouble.

gallerytungsten · 03-11-2009, 11:01 PM

Quote:

Originally Posted by MALCO.New.York

Precisely............But I do know what has worked, from EXPERIENCE, for me.

In your previous post you mentioned the BTU of the unit, which suggests you were talking about a window unit. That's a bit different than sizing a ducted HVAC system with an outside condenser and inside air handler.

MALCO.New.York · 03-11-2009, 11:48 PM

Quote:

Originally Posted by gallerytungsten

In your previous post you mentioned the BTU of the unit, which suggests you were talking about a window unit. That's a bit different than sizing a ducted HVAC system with an outside condenser and inside air handler.

Yessiree!

hvaclover · 03-15-2009, 01:15 AM

Quote:

Originally Posted by MALCO.New.York

To begin................

One can NEVER have TOO big an A/C unit!!!! It will work less-hard than a unit that is "Fringefully Adequate".

If the 5 ton is NOT Economically Prohibitive..............Buy it!!!

Be sure you are buying "good stuffs" with a sufficient EER.

GET THE WARRANTY. I HATE Warranties............But with an A/C, something that NEITHER of us know how to fix, it does make sense!!!

Dude you have been using your face for a Makiwara board again, haven't you? Didn't I tell by PM that is why you make stupid remarks on this board all the time?

Now stop it and go play with your Ninja Turtle dolls.

PS

Bruce Lee didn't know jack about real fighting.

JIM1941 · 03-19-2009, 05:13 PM

Quote:

Originally Posted by knothole

Have the contractors do a "Manual J" load on your house. One that is to big will not run long enough to keep the humidity down and your house will feel damp.

JIM1941---This is the correct method to figure your house load!
Depending on Insulation,type of windows/doors/and insulation(all this taken in consideration in Manuel J) most houese are figured at 450sq.ft.
per ton of A.C. capacity! JIM

bwalley · 03-19-2009, 06:01 PM

Quote:

Originally Posted by JIM1941

JIM1941---This is the correct method to figure your house load!
Depending on Insulation,type of windows/doors/and insulation(all this taken in consideration in Manuel J) most houese are figured at 450sq.ft.
per ton of A.C. capacity! JIM

Figuring a house at 450 ft2 per ton does not work.

My house is a 2 storey house, with 8' ceilings on the 2nd floor 10' on the 1st floor and 19'6" on the foyer, stairs, great room and hallway.

If you figure my house the same as you do a single storey house with 8' celings, my house would not be sized properly.

Depending on where you live will also determine how much heating/cooling you will need.

Rules of thumb do not work in sizing A/C systems.

hvaclover · 03-19-2009, 06:14 PM

Quote:

Originally Posted by JIM1941

JIM1941---This is the correct method to figure your house load!
Depending on Insulation,type of windows/doors/and insulation(all this taken in consideration in Manuel J) most houese are figured at 450sq.ft.
per ton of A.C. capacity! JIM

Wow.

I have seen some rules of thumb.... but that one would over size the dickens in most areas, except may the planet Mercury.

We got guys doing 600sqft here in MI and that ain't right. If you don't use a manual J or have not done enough heat loads to get a feel for the construction methods common to your area, than you better stick to the book.

beenthere · 03-19-2009, 06:46 PM

450 sq ft a ton.

My place is 1650 sq ft.
My A/C is 2.5 tons, and i can maintain 70 on a 98° day, its over sized at 660 sq ft a ton.

It was here before me.

newfy · 03-20-2009, 02:46 PM

Quote:

Originally Posted by MALCO.New.York

To begin................

One can NEVER have TOO big an A/C unit!!!! It will work less-hard than a unit that is "Fringefully Adequate".

If the 5 ton is NOT Economically Prohibitive..............Buy it!!!

Be sure you are buying "good stuffs" with a sufficient EER.

GET THE WARRANTY. I HATE Warranties............But with an A/C, something that NEITHER of us know how to fix, it does make sense!!!

I guess yor more into refrigeration than AC, to big a unit & you will not be removing the humidity. Based on the numbers given, 3 to 3.5 tons cooling.

MooreAirINC · 03-31-2009, 08:40 AM

A 5 ton unit will ruin your life, Dont listen to anything else ,TRUST ME, Like some have said Dont ever go with a contractor that hasent preformed a MANUAL J heat load calc, My ball park is that 3.5 system and i would try it on low speed first, If your head pressure runs to high pick it on to medium but youll be kicked like a chicken

MechAcc · 04-02-2009, 07:01 AM

Option: Put in a 4 or 5 ton 2 stage heat pump or air conditioning system if the duct work size allows. You then have humidity control plus additional capacity for the full design or plus design days. Heat pump will give you heating to a certain outdoor temperature which may be more cost effective than a full electric strip heat, gas or oil heat system.

Now play nice.

Texahoma · 04-06-2009, 11:18 PM

There is no such thing as a rule of thumb when properly sizing the proper load for your house. I can have two identical houses one with the front facing south and the other with the house facing the north. Your load is going to vary. You need to have a ACCA J8 load calculation done. If you want to spend the money your looking at around a $ 1,000 dollars or more depending on what modules you buy.

hvaclover · 04-06-2009, 11:39 PM

HEH, Man J.

I haven't seen any two software load calcs agree yet. Always differ by a1/4 to 1/2 ton.

I see experienced guys get closer than that just by knowing the construction
methods common to their market.