Heat loss on underground piping

larryjbjr

Member
Jan 24, 2017
122
WI
OK I was looking at this website
http://wood-heating-solutions.com/outdoor-furnace-parts/insulated-pex-pipe/

And I noticed that they claim 1.5 to 1.62° heat loss on their three wrap pex tubing. I emailed Randy and asked him if that was both directions or just on the supply side and how much I would lose with only 50 feet run.

Here is his reply:

" at 50ft you would lose .62 degrees supply and return."

My response:

" so, 1.2 deg round trip?"

And his answer:

"No, hot water goes in cold water comes back the .62 is the hot water line the return cold water line has nothing to do with it."

Can somebody clarify this for me please? I thought the water returning was still hot and therefore if you lose temperature on the return it's still heat loss.



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maple1

Minister of Fire
Sep 15, 2011
10,530
Nova Scotia
I'm not into mind reading but I think he means it would lose 0.62 per 50 feet. Which means supply & return would each lose 0.62 in their 50 feet run. That's how I would interpret.

I would also not buy that pipe or anything wrapped like it is - and find those numbers hard to believe.

Get good stuff - Thermopex or Logstor or that type. This is one place you don't want to cheap out, it will come back to bite.

IMO.
 

salecker

Minister of Fire
Aug 22, 2010
1,126
Northern Canada
Spend a bunch of time reading about underground piping.
I was going to buy the bubble wrapped junk.Then i started reading up on hydronics on this site.
I went with foam in trench method.I used Rehaul pipe and asked for at least 4" around each of my 4 pipes in the trench.
It was an expense,but should be a one time expense.
 

larryjbjr

Member
Jan 24, 2017
122
WI
I'd like to get the good stuff, but my budget gives no room for that.

It would be an extra $450 or so. I don't have an extra $450 right now, and the longer I wait in order to save up the $450 the more it will cost as I lose money paying extra propane while I'm waiting.

I figure an extra cord of wood a year is better than an extra year of burning propane, at over $300/month...




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hondaracer2oo4

Feeling the Heat
Jan 18, 2012
414
Canterbury NH
The problem isn't that fact that the wrapped pipe may lose a little more heat than the logstor or thermopex. The problem is that ground water will end up in the lines. It might be 6 months from now or 5 years but it will happen! The black drain tile will get a small puncture(could even come that way from shipping, no way to see a small hole in that stuff ) and once water gets in you will go from burning 5 cords per year to 10 cords per year. You will have to dig up the pipe again and spend the money to buy the good stuff the second time. Do your self a favor and the extra work and spend the $450 because it is really cheap money at the end of the day.
 

maple1

Minister of Fire
Sep 15, 2011
10,530
Nova Scotia
I'd like to get the good stuff, but my budget gives no room for that.

It would be an extra $450 or so. I don't have an extra $450 right now, and the longer I wait in order to save up the $450 the more it will cost as I lose money paying extra propane while I'm waiting.

I figure an extra cord of wood a year is better than an extra year of burning propane, at over $300/month...




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We don't know anything about any of your system - but when it goes wrong it usually really goes wrong. Usually people end up digging it up & replacing, after a winter of constantly feeding their wood burner & the house being cold the whole time because the boiler water getting to it isn't hot enough. If it was a matter of simply burning an extra cord, that would be one thing - but when your house system needs constant 160+ water and it's only getting 150 max because your supply is losing 30 to the ground between the boiler and the house, that's another. Then there's also the creosote condensation & reduced boiler temp effect on the other end if the return water coming back into the boiler is only 100. Which then in turn lowers your boiler supply temps - a vicious circle typically resulting in at least doubling wood consumption. Not everyone experiences that every time of course, but it's happened a lot. Even if the run only loses a very optimistic (for that stuff) 10° each way, your boiler will struggle - with that 20, and another 20 dt for the house draw, that means your boiler will need to raise the water 40° under constant flow to maintain 180 out & keep return above 140 (point of condensation - does your boiler have return temp protection?). Quite hard to do. Things might be OK at first when everything is new, but moisture getting into that insulation is only a matter of time. The thin layer between supply & return lines will also lead to somewhat lower supply temps in the house, as heat want to transfer from the higher temp pipe to the lower temp pipe when they are next to each other.

Comes down to comfort, easier boiler operation - and peace of mind (what I'd consider the big one).
 

larryjbjr

Member
Jan 24, 2017
122
WI
How can I tell if it has return temp protection?


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salecker

Minister of Fire
Aug 22, 2010
1,126
Northern Canada
If it comes to just $450 extra that you need...
Yard sale some stuff that is collecting dust.Get a second job for a weekend.
Everything that Maple1 said should be seriously considered.
 
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larryjbjr

Member
Jan 24, 2017
122
WI
Unfortunately those things are not an option. I am already working all the overtime I can, plus trying to sell my AR, just to get the money to install it to begin with.

But I will take your advice to heart. Maybe for now I will just try to rig it up someway to get by through this winter.

It is only a short ways from my shed so maybe I will build some kind of wooden trough and run some pex through there and insulate it real good to the shed then from the shed to the house just to get by this winter.

I don't want to bury something that is going to be inferior and cause me trouble later on. But I really cannot find the money to buy the good stuff and install it this year.


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maple1

Minister of Fire
Sep 15, 2011
10,530
Nova Scotia
How can I tell if it has return temp protection?


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What do you have?

Typically there would be a bypass loop on the boiler - a pipe connecting just outside the supply outlet with just outside the return inlet. With either a separate pump & controls on that bypass leg, or a thermostatic valve T where it Ts into the return line combined with proper boiler pump location relative to the thermo valve location.

This is done to maintain 140 return temps entering the boiler. If they go lower than that for any amount of time, the cooler return water will cause excessive creosote condensation in the firebox which can cause the firebox to corrode from the inside out.
 

shawntitan

Member
Dec 7, 2007
71
NJ
Careful with that stuff, I have a friend who used the "bubble wrap in black drain pipe" stuff, must have a leak somewhere, he melts snow on a ten foot wide path from his house to his boiler, and it's buried DEEP. I used the spray foam in trench myself almost ten years ago and still have minimal heat loss.
 
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salecker

Minister of Fire
Aug 22, 2010
1,126
Northern Canada
Unfortunately those things are not an option. I am already working all the overtime I can, plus trying to sell my AR, just to get the money to install it to begin with.

But I will take your advice to heart. Maybe for now I will just try to rig it up someway to get by through this winter.

It is only a short ways from my shed so maybe I will build some kind of wooden trough and run some pex through there and insulate it real good to the shed then from the shed to the house just to get by this winter.

I don't want to bury something that is going to be inferior and cause me trouble later on. But I really cannot find the money to buy the good stuff and install it this year.


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Building the above ground box is better than buried inferior lines.
 
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Ashful

Minister of Fire
Mar 7, 2012
15,715
Philadelphia
"No, hot water goes in cold water comes back the .62 is the hot water line the return cold water line has nothing to do with it."

Can somebody clarify this for me please? I thought the water returning was still hot and therefore if you lose temperature on the return it's still heat loss.
I don't own an outdoor boiler, and really don't even know much about them, but I do know Physics. So, take my answer below as theoretical, not based on experience, but physically accurate.

Heat loss is a function of the temperature difference between the heat source (your hot water) and the surrounding space (earth). Double the temperature difference, and you will double your heat loss. So, when numbers like this are given, they're at some assumed water and earth temperature, which are probably typical for your application.

The reason they might not specify temperature drop on the return line is that the temperature of the return water is much lower, and therefore the loss is so much less than that of the supply side that it is not a primary factor for system design. If you happen to know your return water temperature, you could estimate it's loss as 0.62 times (Tr-Te)/(Ts-Te), where Tr is return water temperature, Ts is supply water temperature, and Te is earth temperature.
 

hondaracer2oo4

Feeling the Heat
Jan 18, 2012
414
Canterbury NH
Yes, you are likely correct and appear smart enough to understand those concepts so you will also understand that throwing good money after bad is dumb. The problem again isn't the fact of how much the lines lose if they were tested side by side at the factory. It is when they get buried underground and when the ground water gets into the drain tile type pipe, at the point the lines are useless.
 
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rowerwet

Minister of Fire
You would probably be ok buying the cheap bubble wrap pipe, and installing it above ground in a box that would insulate it from the ground, and protect it from UV and the elements.
My own idea would be a layer of XPS foam between it and the ground, and a luan box over it.
That way you won't be dealing with the ground water issues, and won't be deep in debt.
 

rowerwet

Minister of Fire

rowerwet

Minister of Fire
In my mind I would use 2 inch XPS for the ground layer, with U shaped blocks every 6 inches to keep the pipe off the ground, then 1 inch or 3/4" foam for the sides and roof.
With mor U shaped foam blocks to support the roof.
Then round the corners off and use PMF to seal it all into one weatherproof box.
 

maple1

Minister of Fire
Sep 15, 2011
10,530
Nova Scotia

hondaracer2oo4

Feeling the Heat
Jan 18, 2012
414
Canterbury NH
The rehau is the same as thermopex 1 inch but smaller in diameter than the logstor 1 inch equivalent. It is good high quality pipe, it's the shipping from free heat that will kill the price per foot.
 

maple1

Minister of Fire
Sep 15, 2011
10,530
Nova Scotia
Had a look around that site. I think I would be wary of buying something from them with the smoke & mirrors talk they have on there about other things, like boilers - but the pipe might be OK.

That site name is ringing a distant bell though, not quite sure why or if bad or good. Spidey sense says not good but without remember exactly, don't really know - so all could be well with getting some of their pipe.

I would go for 1-1/4" over 1" though.
 

larryjbjr

Member
Jan 24, 2017
122
WI
I would go for 1-1/4" over 1" though.
I would like to go 1 1/4". But how would I crimp that? I think I'd spend more on the tool to crimp that than I'm prepared to spend


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maple1

Minister of Fire
Sep 15, 2011
10,530
Nova Scotia
I would like to go 1 1/4". But how would I crimp that? I think I'd spend more on the tool to crimp that than I'm prepared to spend


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Not sure - would maybe be worth it to have someone come in with theirs just for that.

But aside from using that wrapped product above that usually leads to moisture intrusion, heat loss & replacement - likely the second most common problem with underground piping is undersizing it.