insulated underground pex

[Tennman]

Thanks for the reply HM. The big old farmhouse you mentioned pretty much describes our 4800 sf old place. When/if I add storage it will be in the boiler barn where all the piping is 1 1/2" black iron. So I can easily run 1 1/2" to storage for those short runs if needed. I started another post specifically asking about the flow velocity in my PEX with the 0013 and EWD assured me I'm ok at a little over 6 fps. Appreciate the inputs from you guys who are installers helping those of us DIYs. Bottom line I now feel good about foaming my existing PEX and restoring my lawn for the last time.

 

[greenheater]

I'm happy with my 140 feet of logstor 1 1/4 inch... but I purchased it 3 1/2 years ago and understand its tougher to find.

 

[heaterman]

Thanks for the reply HM. The big old farmhouse you mentioned pretty much describes our 4800 sf old place. When/if I add storage it will be in the boiler barn where all the piping is 1 1/2" black iron. So I can easily run 1 1/2" to storage for those short runs if needed. I started another post specifically asking about the flow velocity in my PEX with the 0013 and EWD assured me I'm ok at a little over 6 fps. Appreciate the inputs from you guys who are installers helping those of us DIYs. Bottom line I now feel good about foaming my existing PEX and restoring my lawn for the last time.

Flow velocity in pex is probably less critical than copper because of the fact that there are usually far fewer fittings in a given loop. When you are in the 6fps range with copper you will hear a little flow noise but usually no objectionable. The real issue to me is that when you get much above that 6 range you can start to introduce some noticeable deterioration in the fittings, especially short sweep plumbing elbows. I've seen pinholes in copper ells that were only 5-6 years old and the whole fitting could literally be squeezed and deformed with only finger pressure due to how much material had eroded away. As to fittings for your 1-1/4" pex, or any pex for that matter, the more I read and learn about brass fittings, the more I tend to avoid them if possible and go to bronze. Observing what has happened to a few systems using brass fittings with fresh water has me questioning whether they are a good choice if bronze is available. There are chemical interactions that can cause the brass to "de-zincify" and fail structurally. Do a google for dezincification and enjoy the reading.

 

[ewdudley]

Observing what has happened to a few systems using brass fittings with fresh [emphasis added] water has me questioning whether they are a good choice if bronze is available. There are chemical interactions that can cause the brass to "de-zincify" and fail structurally. Do a google for dezincification and enjoy the reading.

Here's one google result:

http://www.hghouston.com/coppers/brass75.htm



Central heating systems

Water in these closed-circuit systems is de-aerated during heating. This suppresses dezincification, even if the water used to fill the system initially is one known to cause dezincification in aerated plumbing systems. Consequently radiator valves, pipe fittings etc. for central heating systems do not have to be of dezincification-resistant brass.

 

[heaterman]

Observing what has happened to a few systems using brass fittings with fresh [emphasis added] water has me questioning whether they are a good choice if bronze is available. There are chemical interactions that can cause the brass to "de-zincify" and fail structurally. Do a google for dezincification and enjoy the reading.

Here's one google result:

http://www.hghouston.com/coppers/brass75.htm



Central heating systems

Water in these closed-circuit systems is de-aerated during heating. This suppresses dezincification, even if the water used to fill the system initially is one known to cause dezincification in aerated plumbing systems. Consequently radiator valves, pipe fittings etc. for central heating systems do not have to be of dezincification-resistant brass.

Ahhhhh yes. But many of the readers here are using brass fittings in open or semi open systems where O2 can easily enter the system.

 

[ewdudley]

...
Ahhhhh yes. But many of the readers here are using brass fittings in open or semi open systems where O2 can easily enter the system.

Good point! I've been kind of locked-in to a all-the-world-is-a-pressurized-system frame of mind.

 

[HeatGeek]

Heaterman, Your last post made me feel somewhat better about my 1 1/4" piping system. Per the Taco TD10 data sheet I knew I'd be exceeding the TD10 maximum 1 1/4" recommended flow rate of 11.2 gpm. With my computed head loss of a little more than 22 feet and assuming my 210kbtu boiler could consistently put out about 170kbtu I computed a required flow rate of 17 gpm (20F deltaT). Those two numbers flow rate and head put me right on the Taco 0013 curve. I had not read of anyone here using more than 1 1/4" PEX so I presumed others were routinely exceeding the recommended flow rate on 1 1/4" PEX. The existing 115kbtu propane furnace was adequate to keep our downstairs adequately warm during our short heating season, so I didn't attempt to do a heat loss. Since I'm about to dig up my PEX to foam insulate, from your experience am I way over pushing the flow rate in that 1 1/4"? Until recently I don't recall ever hearing discussions about 1 1/2" PEX.

The TD10 document implies the gpm limits are to keep flow noise at acceptable limits. But they also say keep flow velocity between 2-4 fps. At 17 gpm and 1 1/4" I'm at 6.25 fps! Now I'm wondering if I need to add a 1" line to my existing 1 1/4". Geez what a learning experience related to the underground part of this system.

Reading between the lines of what info you have posted here I wouldn't get to concerned about it. 1-1/4" will give you plenty of flow to heat your house. Charging your storage with no other load on the system will be the only time you actually need the 17gpm. ......depending of course on how the piping is configured.
As to the availability of 1-1/2 pex, I would say the the majority of our systems (mostly Garn based) go in with that size tube when the entire load is served via a single underground line, so it's out there if you need it.
Remember also that you can reduce your flow requirements by over sizing your heat emitters. As an example, I just visited a job that was done in 2002 where we did the inside piping and HX's after the customer had installed the underground himself. The building is a big old farm house with 5 bedrooms and 2 full baths and the heat load was/is very high per sq ft of floor space. The guy had run a pair of 3/4" pex lines from the OWB to the house which for all intents and purposes is severely undersized. He didn't want to dig it back up and go with bigger tube so we went with plan B. We used one pair of lines for heating and the other for DHW. I ordered him a custom heat exchanger for his furnace, 24"x24" with a four row coil configuration, to help extract heat from the water. I would say we are lucky if the flow rate hits 5GPM on that system and it should be in the neighborhood of 10 under normal design parameters. Suffice to say the darn thing heats and heats well. We got a little over 30* drop by using that ginormous HX in the plenum and when you increase the temp drop the flow requirement of course, is reduced. More than one way to skin a cat

Hi Guys, I'm new to the forum and am in the process of installing a sizable system. Large non-presureized wood boiler is about 450 feet from the house which is further than any installation I have heard of. I've already got an underground line (PEX-FLEX/LOGSTOR dual 1" ID) from the boiler into my shop in the barn at about 130 feet. (Of course the shop is heated first!).

For the house (about 4500 sq ft) I am planning the same 1" ID line because at 450 ft and around $12/ft, the cost is ginormous just for the line. Boiler and house are very close to the same elevation, except I am going under a (drainable) pond that lies between the two. I plan a large circulation pump at the boiler and one at the house. Heat transfer in the house will be via water heat exchangers one for DHW, one for forced hot water heat.

I've read Heaterman's posts on the heat transfer numbers for various size lines, but have not seen much on getting water 450 feet each direction and how that might play into the water line size to use and the overall design. I think 1.25" or 1/5 " line is around $25/ft. Makes me have $ nightmares.

Any comments are welcome.

 

[Tennman]

I built a spreadsheet to do the flow rates and flow velocities required to get the btus from my boiler barn to our house. Built from the Taco Datasheet. Our home is slightly larger than yours. Unless your home is very energy efficient, which ours is certainly not, 1" will be pretty small to pump the required btus/hr to your home. AND we're pretty far south. If you are spreadsheet handy I'd be glad to send so you can see for yourself how the long runs affect the pressure drop and literally how a 1" line limits you when you MUST push water that's heated to no more than 175-180F. You are creating a pipeline of energy. To get the same quantity of energy thru a smaller pipe means the water has to flow faster, which means more drag, electricity... on and on. People here, myself included, with much shorter runs with houses your size run at least 1 1/4. For my house I was concerned 1 1/4 was too small, the reason for my question to heaterman. BTW read the Sticky about my underground adventure. Any way you do it 450 round trip will be priceyu.

 

[HeatGeek]

Thanks much Tennman,

I appreciate the comments and would like a copy of the spreadsheet. Thanks also for the pointer to your stickey which I've now read. House is pretty well insulated, but I agree that length water line scares me. Think my e-mail is available from my profile. Thanks much

 

[woodsmaster]

$25.00 is a little high, more like $16 - $17 for 1 1/4 logstor or thermopex. Still a lot of money!

 

[heaterman]

$25.00 is a little high, more like $16 - $17 for 1 1/4 logstor or thermopex. Still a lot of money!

You can buy 32mm MicroFlex for about $18/ft and that stuff is about the best I've found. Multiple layers of closed cell encased in a 5" flexible shell rather than the usual 4. Very flexible and easy to work with. Not like wrestling with an anaconda.