OT- Gas pack size calculation ?

Climate= Atlanta, GA. Situation= Older house with limited insulation, single pane windows, 12 foot ceilings, 156,000 cubic feet. Natural Gas BTU needed = ?

You do know that 156,000 cubic feet divided by 12 feet yields a house with 13,000 square feet of conditioned space?

This barn will cost a fortune to heat.

You sure you didn't mean 15,600 cubic feet? That yields a 1,300 square foot floor plan.

Anyway, your best bet is to call Atlanta Gas Light (if they still exist) and have them estimate it for you.

Ed in Florida

Rule of thumb ''ballpark figure'', from my apprentice days 40 years back.

BTU = Cubic feet x 3.5 normal positions OR 546,000 BTU

BTU = Cubic feet x 4 exposed positions OR 624,000 BTU

Obviously an efficient and cost effective heating system has to be properly designed.

This may be somewhat useful.

http://www.builditsolar.com/References/Calculators/HeatLoss/HeatLoss.htm


You could probably ask locally what they usually figure for their BTU per sq/ft loss. Someone should have some rough chart they use for sizing systems. Might be somewhere around 20-25.

Windows?

What is the total area of windows in building?

Here's another calc method that may help

http://www.pprbd.org/plancheck/Heat%20Loss%20Table.pdf

http://www.pprbd.org/plancheck/heat_loss.html

Delta T is the temp rise needed in winter to get to 68 degrees. Average January low in Atlanta is 33 so I'd use 35 as the delta T.

***

You might also want to do a DIY version of a blower door (or window) test. Winter is perfect because once you start to suck air out of the house it is really easy to feel the cold air leaking in. Sealing the house should be number 1 on the improvements list.

http://www.energysavers.gov/your_home/energy_audits/index.cfm/mytopic=11190

Steve.

eng4turns said:

You sure you didn't mean 15,600 cubic feet? That yields a 1,300 square foot floor plan.

Click to expand...

D'oh ! Yeah..typo... meant 15,600...sorry..

"Gas pack' never heard the term before. is this something to do with propane tank size. on houses the gas company sizes the gas line and meter for you for you. Unless there is some odd gas use like a bakery or welding they use some standard formula for service size. Like 3/4 or 1" pipe is standard supply line to modern houses. maybe 1/2 in older small house.
Or is this a reference to total gas comsumption of house with all appliancies at fuel throttle.
Bill D.

A gas pac is a packaged gas fired heating unit with electric cooling. Typically sits outside on a pad and the supply and return ducts run thru the foundation and into the crawl space or basement. In some areas where houses are built on slabs, the unit can be curb mounted on the roof and then the supply and return ducts come out of the bottom of the unit and into the attic space.

Don, its typical to size a gas pac based on air conditioning requirements. A unit sized to cool the house will always have plenty of heating capacity to keep it warm in the winter here in the south.

A house that's old enough to have 12 ft ceilings likely has almost no insulation unless its been added later. Assuming the 1300 sq ft is correct, you'd probably want a 3 ton unit in the Atlanta area. That said, there are plenty of contractors who'll quote a 2 ton or 2.5 ton unit in an attempt to be the low bidder.

There's a specific procedure for doing a heat loss/gain calculation for accurate system sizing. A form exists, although I can't remember the form number, published by ASHRAE for doing the calculations in a manner that makes sure you don't miss anything. The lowest level of HVAC license in NC requires the demonstrated ability to do the loss/gain calcs using this form, and I'd assume GA's licensing requirements are similar.

If you walk into a house built within the last 30 years or so, its fairly safe to size equipment based on square footage. But, for an old house, the same numbers where they may be figuring 650 to 700 sq ft per ton will give sizing that's too small during the extremes of hot or cold, so the loads do need to be accurately calculated based on exposure, wall and ceiling construction, insulation if it exists, etc etc. Unless its been renovated, most doors and windows don't fit too well, and the combination of single pane glass plus ill fitment can add up to the equivalent of a pretty good hole in the wall at each window or door location.