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# anyone know of a source for heating loss for un-insulated pipes?

Member Posts: 48
I cannot find any reference to show how many btus are lost in things like this:

hot water flowing in 3/4 copper at say 2,3,4 gpm at say 160. 170, 180 degrees;

The same temps in 1 1/4 cast;

what the temp drop is if when the zone is satisfied and the water sits there at x temp in an un insulated pipe in a basement or exposed attic. Trying to figure out how long till it freezes..

Thanks.

• Member Posts: 616
Hydronics inspired homeowner with self-designed high efficiency low temperature baseboard system and professionally installed mod-con boiler with indirect DHW. My system design thread: http://forum.heatinghelp.com/discussion/154385
• Member Posts: 23,894
Unless it is polished or painted, heated metal is heated metal -- and to a reasonable approximation it will radiate 240 BTU/hr per square foot at steam temperature. At lower temps, less -- and I know someone here has put up the numbers but I can't remember them.

So you figure the surface area of the pipe and multiply...
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
• Member Posts: 7,427
edited February 2016
The Grundfos Handbook has charts that give that info.

Following up on what Jamie said: it's 150 btus per square foot of surface @ 170*.

The GPM will only be a factor as the surface temp drops due to the water temp dropping along the pipe. If you know the supply and return temp, then just use the AVERAGE between them. No GPM to factor that way.
Bob Boan
You can choose to do what you want, but you cannot choose the consequences.
• Member Posts: 48
What I am trying to figure out is if one loses power, and boiler is out, assuming pipes were at 170 degrees FHW. If pipe is exposed in an attic and say its 0 F, my question is the time frame to get things back up and running. Sadly sometimes pipes are run in un-insulated spaces.
• Member Posts: 616
edited February 2016
The rate at which a pipe will lose heat depends on the temperature difference between the pipe and surrounding air. The heat loss is greatest when the difference is greatest. As the temperature difference decreases, the rate of loss decreases. The answer can be determined by using differential equations. Unfortunately, my calculus skills are weak. This could probably be closely approximated using a linear regression analysis in a spreadsheet.
Hydronics inspired homeowner with self-designed high efficiency low temperature baseboard system and professionally installed mod-con boiler with indirect DHW. My system design thread: http://forum.heatinghelp.com/discussion/154385
• Member Posts: 23,894
Take a look at @Brewbeer 's reference,

http://www.warrenforensics.com/2014/03/18/how-long-before-the-pipes-freeze/

-- that is exactly the question which it answers.

And the answer is that it doesn't take all that long... a matter of a few hours, if it's really cold out.

And yes, sadly, pipes are sometimes run in uninsulated spaces. They usually freeze and burst.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
• Member Posts: 69
How long has the piping been run in an exposed attic? Has it frozen before?
• Member Posts: 48
no its never been frozen. I did insulate it. I have a generator if power should go off. My thought was if electricity went out overnight would it be frozen in say 6 hours? My guess is probably. Its copper 3/4 probably M.
And in new housing it would be pex. How does that do in comparison to copper when it freezes?
• Member Posts: 22,655
Yes pex and the various blends are more "freeze tolerant" but with a long enough exposure the tube and fittings can and do split or pop apart.
Insulation slows the energy transfer, but no reasonable amount can stop it. Seal up any areas where the wind (drafts) speed up the heat loss.
I have seen fin tube baseboard freeze inside a heated space when infiltration around the wall framing allowed that arctic blast inside.

If you experience or expect prolonged outages, a generator is one option.

Others keep a few deep cycle RE batteries with either a DC circ piped in the loop, or a small inverter to keep a 120VAC circulator going.

With todays low draw ECM circulators that should buy you hours maybe days with enough battery capacity.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream