Sizing Furnace and AC

Originally Posted By: abishop
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How do i know if the unit is large enough for a home?


Furnace 75,000 BTU


AC 1/4 hp


Is there a square foot to size ratio?
Thanks


--
Andy Bishop
Bishop Home Inspection, LLC.
bishophomeinspection@charter.net
269-686-6485

Originally Posted By: bking
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A/C rating should be in tons not hp.


75,000 btu furnace in your area would be for about a 1400SF house I would guess.


Basic Info only: (very complicated subject)
600 SF per ton unless it has zoning that is properly setup then you can do 1000 SF to even 1200 SF per ton depending on things like quality of windows, insulation, ceiling height, climate etc.

The zoned systems will run non-stop to keep up and if you like your upstairs 70 degrees in 90 degree weather you probably will be disappointed. Cheaper builders are using these zoned systems but if done correctly, which means a larger unit and more air returns they can work very well on higher end homes.


--
www.BAKingHomeInspections.com

Originally Posted By: abishop
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So if you have 1650 upstairs. You would need approximately a 3 ton. What if it is and unfinished basement that is a walkout and i am sure they will finish it someday. Then you would need about a 5 ton. Of course you could say the basement is cooler usually and maybe get away with a 4 ton? Is that what you guys would say?


Thanks



Andy Bishop


Bishop Home Inspection, LLC.


bishophomeinspection@charter.net


269-686-6485

Originally Posted By: jwilliams4
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Equipment sizing should never be determined by a ‘rule of thumb’.


The MANUAL J was developed for this purpose. There many factors

that determine the size of equipment. Windows, doors, leakage,

insulation, position of house to the elements, landscaping...

You suggested 1650sf = 3 tons of air...my house is 2500sf and is

quite comfortable with 2 1/2 tons, thank you. The efficiency of the

equipment is another factor to consider.

Better to just check for operation and don't get hung up on efficiency.

If there is any question refer an HVAC professional look at it.


--
"not just an inspection, but an education"

Originally Posted By: dandersen
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Quote:
A/C rating should be in tons not hp.


Not, For anyone (other than J, who is about my age ![icon_smile.gif](upload://b6iczyK1ETUUqRUc4PAkX83GF2O.gif) )HP can be directly converted to BTU/hr.

But for now, let's just let this one rest.

Quote:
Is there a square foot to size ratio?
400sf/ton where I live (if you dare).

You are not required to do Engineering Evaluation (NACHI SOP) , The heating/cooling engineers of the world have a full time job working on this and they can't agree. So, just keep out of the quicksand.


Originally Posted By: jhugenroth
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jwilliams4 wrote:
my house is 2500sf and is

quite comfortable with 2 1/2 tons, thank you.


This is why a "rule of thumb" is dark territory. Around here, a 2500 sq ft home would need 5 tons.


Originally Posted By: phinsperger
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http://www.nachi.org/bbsystem/usrimages/l/load.gif ]


For a bit more info on sizing furnaces and air cond see
http://hvac-talk.com/vbb/showthread.php?threadid=33866


--
.


Paul Hinsperger
Hinsperger Inspection Services
Chairman - NACHI Awards Committee
Place your Award Nominations
here !

Originally Posted By: Gary Reecher
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Rule of Thumb icon_question.gif Supposed to use your fingers. Walk across the street and stand on the curb and hold up your hand. If 4 fingers covers the house you need a four section boiler to heat the house. Four fingers not enough to hide the house use the fingers on your other hand. Five fingers five sections, six fingers six sections.



Gary Reecher, CM


HVAC Service Technician


MechAcc's Carbon Monoxide Site Links

Originally Posted By: John Bowman
This post was automatically imported from our archived forum.



Gary Reecher wrote:
Rule of Thumb ![icon_question.gif](upload://t2zemjDOQRADd4xSC3xOot86t0m.gif) Supposed to use your fingers. Walk across the street and stand on the curb and hold up your hand. If 4 fingers covers the house you need a four section boiler to heat the house. Four fingers not enough to hide the house use the fingers on your other hand. Five fingers five sections, six fingers six sections.


Do you hold your hand horizontal or vertical.