Pipe Volume
- Thread starter tel
- Start date
R
Rancher
Guest
Since you didn't give me the diameter of the pex pipe, you'll have to make the calculations yourself.
Pi x R squared x lenght (500' or 6,000")
Pi = 3.1415
R = Radius of the pipe, i.e. half the diameter.
So for 3/4" pex
3.1415 x (.375 x .375) x 6,000 = 2650 cubic inches
2650 / 144 = 18.4 cubic feet
18.4 X 7.48 = about 138 gallons (7.48 gal per cubic foot)
Rancher
Pi x R squared x lenght (500' or 6,000")
Pi = 3.1415
R = Radius of the pipe, i.e. half the diameter.
So for 3/4" pex
3.1415 x (.375 x .375) x 6,000 = 2650 cubic inches
2650 / 144 = 18.4 cubic feet
18.4 X 7.48 = about 138 gallons (7.48 gal per cubic foot)
Rancher
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Mikey
Aspiring Old Fart, EE, computer & networking geek
Don't forget to subtract the pipe's wall thickness when you compute the radius. PEX complies with SDR 9, so the wall thickness is 1/9 of the diameter. For 3/4" pipe, that's .083", so making this adjustment throughout, and using 1728 cu in per cu ft (thanks, jimmym) I get about 7 gallons.
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Mikey
Aspiring Old Fart, EE, computer & networking geek
OK. For 1/2" PEX, about 3 gallons per 500 feet.
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Mikey
Aspiring Old Fart, EE, computer & networking geek
I need to go back to 3rd grade.
Correcting for lots of screwups, the real numbers are as edited (or as will be edited shortly) above. I think.
Correcting for lots of screwups, the real numbers are as edited (or as will be edited shortly) above. I think.
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Thanks guys..
That was about what I thought.. My problem is I am thinking of having underfloor hotwater heating system installed in my family room, and the contractor is telling me I need about a 30 gal elec hotwater tank, seems alot to me.. Any thoughts?
Cheers
tel
That was about what I thought.. My problem is I am thinking of having underfloor hotwater heating system installed in my family room, and the contractor is telling me I need about a 30 gal elec hotwater tank, seems alot to me.. Any thoughts?
Cheers
tel
R
Rancher
Guest
Opps, not enuf coffee
Mikey
Aspiring Old Fart, EE, computer & networking geek
The problem is you're not just heating the 3, 7, 10, or however many gallons it might be. You're maintaining a flow at a desired temperature. Depending on the flow rate and temperature differential, you need a certain number of BTUs, which translates into a certain number of kVA, kwH, etc., which determines the size of the WH. There are a couple of guys here who can do these calculations off the top of their head, but they'll need more data than we have so far. The odds are your contractor has already done these calculations (ask him to explain) and determined the 30gal WH is appropriate.
Bob NH
In the Trades
Before you look at gallons, you need to consider BTUs per hour.
How many BTUs per hour do you need?
Then you need a heater that will deliver that many BTUs per hour.
1 kW = 3413 BTU per our if you are heating with electricity.
If you are looking at a gas heater, then you need to look at the rating of the heater, usually in Net BTU/hour.
How many BTUs per hour do you need?
Then you need a heater that will deliver that many BTUs per hour.
1 kW = 3413 BTU per our if you are heating with electricity.
If you are looking at a gas heater, then you need to look at the rating of the heater, usually in Net BTU/hour.
hj
Master Plumber
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heater
6 gallon, 30 gallon, or more is basically immaterial. You have to size it for the recovery, not the storage, so the energy input is what counts, not the size.
6 gallon, 30 gallon, or more is basically immaterial. You have to size it for the recovery, not the storage, so the energy input is what counts, not the size.
BubbaBob
New Member
Make it simple and economical
I've just built a 706 sq ft yurt (google them...they are interesting) and for heat I installed radiant floor heating using a Takagi TK-Jr propane tankless heater. My floor has 700 linear feet of 1/2 pex-a in 4 zones, and the expansion tank is a 2.2 gal Watts, which is more than enough.
Inexpensive, economical operation, efficient, trouble free. What more could one ask for?
I've just built a 706 sq ft yurt (google them...they are interesting) and for heat I installed radiant floor heating using a Takagi TK-Jr propane tankless heater. My floor has 700 linear feet of 1/2 pex-a in 4 zones, and the expansion tank is a 2.2 gal Watts, which is more than enough.
Inexpensive, economical operation, efficient, trouble free. What more could one ask for?
Lakee911
I&C Engineer (mostly WWTP)
What's it for?
Gary Slusser
That's all folks!
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We already have 6 solar panels and 6 6volt AGM batteries BUT I'll ask for 2-3 more solar panels, 2-4 more AGM 6 volt batteries and a central vac system for my totally off grid motor home. Then I wouldn't have to run the generator at all. A yurt is immovable LIKE A HOUSE!
hj
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volume
And to mess up the original calculations, PEX i.d. is NOT 3/4". It is between 9/16 and 5/8 meaning that its volume is about 75% of copper tubing.
And to mess up the original calculations, PEX i.d. is NOT 3/4". It is between 9/16 and 5/8 meaning that its volume is about 75% of copper tubing.
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