How large a Cental Air conditioning unit do I need?
 

My house is about 2,000 Sq. Ft, in New Jersey. We have Vinyl Siding.
The contractor suggested a 2.5 ton unit (30,000 BTU) based on teh
Windows, size, etc.

I wonder if thats large enough?

We currently have a number of individual units, and their total BTU is
around 45,000.
Even using 20* 2,000 SQ/Ft = 40,000 BTU

The contractor is reputable, and seems knowledgeable. I don't think a
larger unit costs much more and generally contractors will be happy to
sell a more expensive unit, as they make a bit more.

I'm just concerned that 30,000 is not enough.

How large a Cental Air conditioning unit do I need?
 

wrote:
My house is about 2,000 Sq. Ft, in New Jersey. We have Vinyl Siding.
The contractor suggested a 2.5 ton unit (30,000 BTU) based on teh
Windows, size, etc.

Sounds like the contractor is guessing.
Have him/her perform a "Manual J" heat gain / loss calculation.

http://www.proctoreng.com/articles/bigger.html

How large a Cental Air conditioning unit do I need?
 

On Wed, 01 Feb 2006 14:23:17 GMT, "Travis Jordan"
wrote:

wrote:
My house is about 2,000 Sq. Ft, in New Jersey. We have Vinyl Siding.
The contractor suggested a 2.5 ton unit (30,000 BTU) based on teh
Windows, size, etc.

Sounds like the contractor is guessing.
Have him/her perform a "Manual J" heat gain / loss calculation.

http://www.proctoreng.com/articles/bigger.html


If they didn't use it to begin with, what makes you think they know
how to use it. Garbage in is garbage out.

To the OP--
Either get a qualified hvac person to do a load calc or use the rule
of thumb that you need 1 ton per 800 sqft area (for southern climates,
decent insulation, normal ceiling heights) which sounds like what the
contractor is using. You could also talk to others in your area and
see what size homes and ac's they have and with a little math, figure
out what size your's should be. If you are that worried (tho I think
2.5 ton is okay) go with the 3 ton unit.

How large a Cental Air conditioning unit do I need?
 

mad hatter® wrote:
To the OP--
Either get a qualified hvac person to do a load calc or use the rule
of thumb that you need 1 ton per 800 sqft area (for southern climates,
decent insulation, normal ceiling heights) which sounds like what the
contractor is using. You could also talk to others in your area and
see what size homes and ac's they have and with a little math, figure
out what size your's should be. If you are that worried (tho I think
2.5 ton is okay) go with the 3 ton unit.

I guess you didn't read the article.

http://www.proctoreng.com/articles/bigger.html

The "square-foot-per-ton" sizing method avoids calculating the cooling
load of the building and proceeds directly from the square footage of
the building to the size of the air conditioner. No contractor submitted
such a method for approval but a number of contractors reported that
they often used this method, or knew others who did. In a study by the
Florida Solar Energy Center, 25% of the contractors reported that they
size by floor area (see "How They Size Air Conditioning Systems in
Florida," above).
While this approach is rapid and simple, it does not account for
orientation of the walls and windows, the difference in surface area
between a one-story and a two-story home of the same floor area, the
differences in insulation and air leakage between different buildings,
the number of occupants, and many other factors. In some cases
contractors attempt to cover these variables by categorizing the home as
low (a new home in a moderate climate), average, or high (an old home in
a hot climate) but this method also falls short of properly sizing air
conditioners.

How large a Cental Air conditioning unit do I need?
 

On Wed, 01 Feb 2006 20:07:37 GMT, "Travis Jordan"
wrote:

mad hatter® wrote:
To the OP--
Either get a qualified hvac person to do a load calc or use the rule
of thumb that you need 1 ton per 800 sqft area (for southern climates,
decent insulation, normal ceiling heights) which sounds like what the
contractor is using. You could also talk to others in your area and
see what size homes and ac's they have and with a little math, figure
out what size your's should be. If you are that worried (tho I think
2.5 ton is okay) go with the 3 ton unit.

I guess you didn't read the article.


Guess you didn't read my post either. I wrote "rule of thumb". I
guess you don't know what that means?? Further I wrote other
solutions too but I guess you chose to ignor or address them too.

How large a Cental Air conditioning unit do I need?
 

mad hatter® wrote:
Guess you didn't read my post either. I wrote "rule of thumb". I
guess you don't know what that means?? Further I wrote other
solutions too but I guess you chose to ignor or address them too.

Your suggestion that the OP "qualified hvac person to do a load calc" is
the right one - didn't mean to de-emphasize that, sorry.

Having said that, none of the 'adjustment' suggestions you made will
result in an accurate heat gain / heat loss calculation. And in my area
of the country the local permitting agencies won't let you get away with
anything less than an ASHRAE-approved load calculation.

How large a Cental Air conditioning unit do I need?
 

On Thu, 02 Feb 2006 15:34:02 GMT, "Travis Jordan"
wrote:

mad hatter® wrote:
Guess you didn't read my post either. I wrote "rule of thumb". I
guess you don't know what that means?? Further I wrote other
solutions too but I guess you chose to ignor or address them too.

Your suggestion that the OP "qualified hvac person to do a load calc" is
the right one - didn't mean to de-emphasize that, sorry.

Having said that, none of the 'adjustment' suggestions you made will
result in an accurate heat gain / heat loss calculation. And in my area
of the country the local permitting agencies won't let you get away with
anything less than an ASHRAE-approved load calculation.


Sorry accepted. As to whether he requires a load calc, we don't know
but if he does, I think his orig post is answered immediately.
Therefore this thread has been based on "not" required.

I was just trying to suggest other ideas besides a load calc for the
OP. I was not trying to say those ideas were better than a load calc
by a qualified hvac person.

How large a Cental Air conditioning unit do I need?
 

mad hatter® wrote:
I was just trying to suggest other ideas besides a load calc for the
OP. I was not trying to say those ideas were better than a load calc
by a qualified hvac person.

On that we would certainly agree!

Thanks for the follow up, and enjoy the weekend.