BTU's per square feet

[jmo90280]

I know theres alot to consider (light,windows, ect) but in general what would u use?

[dlove]

500 sq.ft. per ton

2000 sqft house 4 ton unit. In most cases after you do a study you will fall somewhere more or less close to that.

Did i just hear an ME curse?

[beshvac]

500 sq.ft. per ton

2000 sqft house 4 ton unit. In most cases after you do a study you will fall somewhere more or less close to that.

Did i just hear an ME curse?

Most are nowhere near that. Manual J is the only way to go.

I live in a 2000sqft house....my 3 ton is too big

[jetstream]

I'm in a 2400 sq foot split level with a 35 yr old 8 SEER unit and I'd say it's sized just right.

By your R of T I'd have a 5 T unit in here which would blow my ductwork to bits.

[rundawg]

Most are nowhere near that. Manual J is the only way to go.

I live in a 2000sqft house....my 3 ton is too big

500 sqft/ton is so old schooL.

I have 3500 sqft. and my 4 tons is just right.

I can't imagine how humid my place would be with 6.5 tons (or the nearest size - 6 tons ).

[BaldLoonie]

You can take the same house and put it on 3 different lots facing different directions and you'll need 3 different sized A/Cs. Take the same house and move it north or south and you'll change the load some more. A rule of thumb gets you nowhere accurately. Better off standing across the street, holding you hand up and the number of fingers it takes to cover the house is the number of tons it needs

[hvacbrean]

my boss lives by rule of thumb, thanks all you more "seasoned" techs for helping us newer ones know the right way. hacks come from bad teachers

[dave sulz]

We talk about this all the time on change outs where the new unit is not the same size.

[dlove]

500 sqft/ton is so old schooL.

I have 3500 sqft. and my 4 tons is just right.

I can't imagine how humid my place would be with 6.5 tons (or the nearest size - 6 tons ).

true old school but he said rule of Thumb

If someone, said hey i got a 2000sqft house, sits on a lot no shade, bad windows etc. built 1980.. I would tell them 4 ton for budget purposes. Of course you will need to do a study. But that was not his question.

If you told someone a budget # to install a 4 ton unit. regardless if they needed a 3 ton or 4 ton how much cost difference is there? not a whole heck of a lot. If they can't afford the 4 ton they sure as heck cant pay the 3 ton cost. Unless you pay a hack !


yes I'm old school. But people will waste your time, ask for quotes when they cant afford to install anything. When i give a rule of thumb based on their description and they don't cry at the cost. I then say would say "but lets do a study and see what you really need. could be more or could be less.

Everyone here has good points, but a rule of thumb has it place and will never go away. Sometimes that's called experience.

the next time you find yourself asking someone "hey what do you think that would cost" you will get a rule of thumb answer and you all done that!

when someone comes up to you with a quote to install an AC system you may say , yeah sounds right, or wow sounds high! you just gave your rule of thumb thought...

[terryp1]

While a R of T is simple, it more often than not results in an oversized system which costs the home owner more money to operate and may not control the humidity. Not only does the orientation of the house make a difference, the shape of the house will drive the heat gain. A square house is more efficient than a long rancher. It takes less than 30 minutes to do a simple manual J.

[BaldLoonie]

If someone, said hey i got a 2000sqft house, sits on a lot no shade, bad windows etc. built 1980.. I would tell them 4 ton for budget purposes. Of course you will need to do a study. But that was not his question.

If you told someone a budget # to install a 4 ton unit. regardless if they needed a 3 ton or 4 ton how much cost difference is there? not a whole heck of a lot. If they can't afford the 4 ton they sure as heck cant pay the 3 ton cost. Unless you pay a hack !

Cousin in KY just sent me a drawing of her 2000 sq ft ranch with no shade but decent windows. Using HVAC-Calc, I spent a few minutes and crunched it. Using R11 walls and ceiling, which I told her we need to upgrade the ceiling, my calcs greatly different from what is installed.

Living room, family room, dining room, kitchen have a 100K 80 and 2.5 ton A/C. Calcs say with this insulation 60K furnace and 1.5 ton A/C

3 bedrooms and 2 baths, about 700 sq ft with no east or west glass and no doors, have 80K 60% and 2 ton A/C. Calcs say 40K furnace and 1 ton A/C.

So for this 2000 sq ft, they have 180K heat and 4.5 tons A/C where they need less than 100K heat and 3 tons cooling. With insulation added to ceiling, the whole house is barely over 1.5 tons A/C and they have 4.5 tons!

Oversized equipment isn't about affording, it's about comfort and efficiency. Short cycling equipment isn't efficient. Oversized A/Cs don't dehumidify and with today's stuff, that's even more of a problem. The 70s relics she has had a low sensible heat ratio and got to a cold coil faster than the high efficiency stuff of today.

[meplumber]

He is another old school opinion on rule of thumb.

I use rule of thumb as a troubleshooting tool. I teach my techs to do the same.

If they walk into a building and they see a boiler that is short cycling and they suspect oversizing. They know that up here, you can expect 45, 40, 30, or 25 btu/sq ft depending on age of the structure, usage, and insulation. It isn't what you size equipment by, but it gives you a starting point that you can derive on the fly in the field.

Same with HVAC. The ROT's give you a starting point. If you walk into a Dental Clinic and see a 3 ton unit trying to service 2,500 sq ft with all their equipment and patients, then you know there might be a problem. Just an example.

It is just that. A Rule of Thumb. Something to start with. If used as they were intended to be used, then you should be ok.

[rundawg]

true old school but he said rule of Thumb

If someone, said hey i got a 2000sqft house, sits on a lot no shade, bad windows etc. built 1980.. I would tell them 4 ton for budget purposes. Of course you will need to do a study. But that was not his question.

No one will argue that rule of thumbs aren't used daily in this business to give people estimates, or ideas of what would work in their home.

The point I was trying to make, which I failed to do by saying "OLD SCHOOL", was that a statement of "500 sqft/ton" is just as much of a WAG, as is "you have a 3 ton now, lets put in another 3 ton unit", or "from my vast experience we usually install this size unit for this type of home".

I just feel that giving the OP any answer other then "do a manual J", just encourages these Old School "rules of thumb" for sizing equipment.

[courttech]

general rule...17 btu/sq ft.
when sizing a heat pump option if the structure has above average heat loss or is not utilizing ac...up sizing up to 25% on the first calculation can be done.
eg. 2000sqft x 17+3400 btu (3 ton) x 1.25 = 42500 (3,.5 ton)

If you go with a two stage unit, ac problems from over sizing wont come into play as much,you can give the home owner a larger unit more closely matched to their heat loss and the system wont utilize the back up heat as much if at all.
Usually a retro fit from another heat source will have questionable duct sizing which will give a noisy/higher velocity air flow from the needs of the 400 cfm/ton for the heat pump, when a two stage is used it will run on first stage most times at a reduced fan speed giving a quieter air distribution system with out costly sheet metal alterations.

[jetstream]

I'm in a 2400 sq foot split level with a 35 yr old 8 SEER unit and I'd say it's sized just right.

By your R of T I'd have a 5 T unit in here which would blow my ductwork to bits.

I notice my post doesn't make sense without the important part which is that it's a 2 Ton system.

[terryp1]

Many homeowners are starting to become aware energy costs in addition to the installation cost. There is no way that an oversized system can meet the advertised SEER. A rule of thumb that is proven for a specific area may be ok, but you must remember that design temperature and humidity levels can change drasticaly from one location in a state to another location. A ton per sq foot rule fails to consider the design temps, the building features such as insulation and windows. For quote purposes, you don't have to do a room by room, but you run the risk of finding surpises in the distribution system. The single most important factor in the installation of a HVAC system is the quality of the installer. That quality starts with the understanding of what is needed to properly heat and cool a residence.

[beenthere]

I know theres alot to consider (light,windows, ect) but in general what would u use?

Around here, you could have anywhere from 600 sq ft per ton to a little over 900 sq ft per ton. Varies with house type, townhouse(inside or outside), rancher, 2 story, etc. Then of course windows, and insulation along with infiltration.

Need to learn the construction practice for your area, for the different years. Then you should after sometime get a good idea what a house might need when you drive up and look around a little.

Doesn't take long to do a block load.

Keep in mind that a 2000 sq ft house with a 4 ton unit moving 1400CFM with a 24 degree coil delta is only doing around 32,000BTUs sensible. Meaning a lot of its sensible and latent capacity is just being wasted keeping the compressor cool, instead of the house.

[dlove]

Around here, you could have anywhere from 600 sq ft per ton to a little over 900 sq ft per ton. Varies with house type, townhouse(inside or outside), rancher, 2 story, etc. Then of course windows, and insulation along with infiltration.

Need to learn the construction practice for your area, for the different years. Then you should after sometime get a good idea what a house might need when you drive up and look around a little.

Doesn't take long to do a block load.

Keep in mind that a 2000 sq ft house with a 4 ton unit moving 1400CFM with a 24 degree coil delta is only doing around 32,000BTUs sensible. Meaning a lot of its sensible and latent capacity is just being wasted keeping the compressor cool, instead of the house.

I find it funny everyone points out that i said to figure a 4 ton for a 2000 sq house. I could of said 2 ton and got the same response. When we are just talking in round about figures.


SO my main point is still valid. if its not 500 sqft. then use 600 or 900, if that is what your used to seeing in your area. That's what we are talking about, when your familiar with the area you work in giving a Rule of thumb is not out of line for a fast budget #. How many times do i get ask how much to install a complete system. Drive out there, do my calculation, spend time figureing out duct work layout. Maybe call a guy to run the electrical, ect ect... to find out from the customer ...Oh i cant pay that..


But than sometimes they tell you their budget..But you still have to go through the same process because you need to cover yourself. If you don't they will say but YOU said bla bla bla...

He ya go you price shopper. 2000sqft house...cost XYZ...could be more, could be less. Can you handle that? just don't waste my time...

[beenthere]

I find it funny everyone points out that i said to figure a 4 ton for a 2000 sq house. I could of said 2 ton and got the same response. When we are just talking in round about figures.

I think you missed the point. I used 2000 sq ft to show that it could be 500 to 900 for a 2000 sq ft house in my area. No one sq ft ROT covers every 2000 sq ft house in this area.

[dlove]

I think you missed the point. I used 2000 sq ft to show that it could be 500 to 900 for a 2000 sq ft house in my area. No one sq ft ROT covers every 2000 sq ft house in this area.

I understood what you meant and agree with what you said.

but its still funny how many hard points of view we got when we are just talking in round about figures.

I got a 4000 sqft house made of Styrofoam 4 feet thick and can cool it with a ice cude and a fan