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# Rules of Thumb and Heating Formulas?

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Member Posts: 1,512
Howdy Wall Citizens,
I have the first draft complete on my new book on Heating Rules of Thumb and Formulas. I was wondering if you have any rules of thumb, secret calculations, or formulas you like to use and think would be beneficial to other wrench twisters like myself. The book is about 180 pages already. I never knew how much we had to know.
Thanks
Ray
Ray Wohlfarth
Boiler Lessons

• Member Posts: 494
edited January 2019
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Ray,
How about the value of 231? Cubic inches in a gallon; add a decimal point & 2.31 feet water column equals 1 psi.
• Member Posts: 1,512
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@MikeL_2 I like that thanks
Ray Wohlfarth
Boiler Lessons
• Member Posts: 903
edited January 2019
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Related, but uses basics to remember it.

A cube of water 1 foot on each side weighs 62.4 pounds
Area of bottom of cube is simply = (12x 12) =144 square inches
So pressure on bottom is 62.4/144 = .4333 pounds/sq inch ( psi)
That's .433 psi /foot of depth

If using oil with a specific gravity of .7 that pressure is .7 x .4333 =0.30 psi/ft
Which means a hose of that oil 10 ft tall will make 3 psi at bottom.
(check SG, gasoline = ~.7 , think #2 oil is higher)

I did so much sonabouy design work I can't forget water weighs ~ 62.4 #/cubic foot ---- ( this is it's density)
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Thanks @Leonard I appreciate it
Ray Wohlfarth
Boiler Lessons
• Member Posts: 903
edited January 2019
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Interesting side note ( for teaching maybe)
0.433 psi /foot of depth .... means 1,000 ft underwater it's 433 psi

And at bottom of Mariana Trench , the deepest known point in Earth's oceans. 36,070 feet depth means pressure is ~15,600 psi
(ignores that salt water is little heavier than 62.4 #/CF fresh water)
• Member Posts: 15,605
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Not hydronic but a piece of ductwork 1 square foot (12" x 12") will carry 1cfm with a velocity of 1 fpm. I use it all the time when I forget/can't find my ductulator.

fuel oil 1" of vacuum for every foot of vertical lift + .5" vacuum for every foot of horizontal run.

1000 btu/lb of steam. lbs of steam =lbs of condensate. lbs of condensate/8.33=gallons of condensate.

Air handle capacity is 400-450 cfm/ton of cooling
• Member Posts: 4,699
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You have the math constant for a 45 degree angle? 1.414? The plumbing pros use the math, the others hold tape measures in the air and give it their best guess
Gary Wilson
Wilson Services, Inc
Northampton, MA
gary@wilsonph.com
• Member Posts: 4,699
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A chart I keep in my cloud
Gary Wilson
Wilson Services, Inc
Northampton, MA
gary@wilsonph.com
• Member Posts: 1,512
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wow Im busy writing notes Thanks Lots of great ideas
Ray Wohlfarth
Boiler Lessons
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@JohnNY My hero lol
Ray Wohlfarth
Boiler Lessons
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Pressure drop = Longest run in feet. Add 50%. Times .04 . This is your head in feet. Dan says figure 6 feet per 100 ft of pipe.
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Formulas used to calculate annual energy costs:
Natural Gas (BtuHr loss of House / AFUE of appliance) X (Htg Load Hrs /100,000) X .77 X Gas rate per 100 cf = cost to heat.

L. P. Gas (BtuHr loss of House / AFUE of appliance) X (Htg Load Hrs /91,500) X .77 X Gas cost per gallon = cost to heat.

Oil (BtuHr loss of House / AFUE of appliance) X (Htg Load Hrs /138,000) X .77 X Oil cost per gallon = cost to heat.

Heat Pump (BtuHr loss of House / HSPF) X (Htg Load Hrs / 1,000) X .77 X Electric rate per kWh = cost to heat.

Electric Resistance (BtuHr loss of House / 3.143) X (Htg Load Hrs / 1,000) X .77 X Electric rate per kWh = cost to heat.

Cooling Costs (BtuHr gain of House / SEER) X (Cooling Load Hrs / 1,000) X .77 X Electric rate per kWh = cost to cool
8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

Two btu per sq ft for degree difference for a slab
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Thanks @Alan (California Radiant) Forbes Appreciate it
Ray Wohlfarth
Boiler Lessons
• Member Posts: 22,244
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Kw to btu X 3.41
Heat= 8.33v (delta t)
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
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Thanks @hot rod_7
Ray Wohlfarth
Boiler Lessons
• Member Posts: 2,282
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Most important rules are maximum fpm for ducts and maximum fps for pipes. Flout them and you'll see.
• Member Posts: 3,113
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I don’t think it’s a hvac formula but here it is who am I making the bill to and will that be cash or check I believe all formulas are nil until it’s fiqured out who paying even when upfront w rates hourly charges are discussed there’s always a air of you charge to come out . Yes sir re on another note I recently thought to myself while look at a job what trade is worse off for the future fitters or tin knockers and which has more hack trunk slammer I came away more confused and realized it’s not that there hacks it’s just about the money and the lack of pride nor care they take in what they do a long lol Peace and good luck clammy
R.A. Calmbacher L.L.C. HVAC
NJ Master HVAC Lic.
Mahwah, NJ
Specializing in steam and hydronic heating