The Price of Copper

[Eric Johnson]

The other day I got a quote for a retail copper coil heat exchanger for my tank, just to put things into perspective as I still struggle to decide what to do. This helped: $3,500.

I called my local HVAC supply house, and their price (I assume retail) for 1" soft copper was $5.50 per foot, minimum 60 feet, plus sales tax (9% around here).

One-inch pex-al-pex (no minimum) goes for $1.40 per foot, plus shipping.

The best estimate for replacing copper with pex-al-pex is 3X as much pex to equal the heat transfer of copper.

On paper, I would need about 200 feet of copper coil do do the job, or 600 feet of pex-al, but I think I could get by with less of each.

Something to ponder over the winter as I play around with the much cheaper flat plate heat exchanger option.

 

[titan]

Crazy-Ain't it?The price increases for copper the past couple years are scandalous.....I cringe when I quote projects for customers now as copper prices seem to change on a daily basis.I hope your plate exchanger works out for you,how large is it?I've installed various smaller plate units before(mostly3") and some of those little puppies go for $1600.00.Just thinking out loud here,but if you had to make your own exchanger-would black-iron pipe work for ya?Certainly cheaper but may provide lesser heat transfer.

 

[Eric Johnson]

I've considered black iron, Titan. The fittings are certainly cheaper. I've also thought about a couple of cast iron radiators. I'd say both are possibilities for my 1,500-gallon "expansion tank."

The flat plate I have is a 150,000 btu/hr number that I paid about $350 for about 4 years ago, as I recall. I heated the whole house with it for three years when my old boiler was full of glycol, so I know it can do the job if I set it up right. Currently I have one (3 speed) Grundfos pump hooked up to it on the tank side, so it's either going to be good at stashing heat or recovering it, unless the tank mixes up too much. Of course, the main system pump is moving pressurize water through the other side. But if I can get some stratification, I may try to put in another pump going in the opposite direction, so that I get flow one way when storing heat and flow in the other direction when recovering it. Attached is a drawing. If there are no flow controls involved, do you think these circulators (the Grundfos and a Taco 007) will pump "through" each other, or should I build some kind of a bypass with a check valve?

 

[titan]

Eric,here's my 2 cents worth:I personally don't think that two pumps in such close proximity would work to their capacity,one would likely hinder the other.I'm trying to sort out exactly what you're looking to do with the exchanger and tank,bare with me here;are you planning to heat the tank via the EKO and exchanger,then later redirect the flow to pull the stored heat from the tank via the exchanger and send this water to your house' rads?

 

[Eric Johnson]

A picture probably explains it better. Here's the rough basic outline of what I'm trying to do. Everything is hooked up pretty much per this diagram except for the tank. At the moment, I'm direct piping the greenhouse off of the 3/4-inch line exclusively, and the return water is going back to the EKO, not into the gas boiler as shown. When the aquastat on the return line of the EKO drops to 160, the three-way zone isolates the wood loop to allow the boiler to recover, and the house side of the system essentially goes into heat recovery mode.

This is more complicated than it has to be. I've since learned that two heat exchangers in the tank would be much simpler: water loops between the EKO and the bottom hx; water loops from the gas boiler through the hx on the top. And that may be the way I eventually decide to pipe it. As it is, it works pretty well--just no storage yet.

 

[titan]

So you'd use a couple heat exchangers instead of just having a supply and return line inout of that storage tank to heat whatever?Just curious.

 

[Eric Johnson]

That would probably be the best way to do it, if I had two heat exchangers at my disposal. Which I don't. Instead I'm trying to get the flat plate to do double duty, much like pumping both ways through a coil.

 

[Nofossil]

I never would have been able to do my heat exchanges the way I did if I had to buy copper at today's prices. I still like the idea of immersing a black iron radiator. I think you can get them cheap, they have gobs of surface area, and they should last a good long time. I've also speculated about using an automotive radiator or two. They're designed to work at 15 psi and 180F, which is about right. Again, plenty of surface area, though you'd have to count on thermal convection to move water through them. I expect you'd have to mount them flat to help that work.

A stainless fab shop here had a whole pile of low-grade stainless pipe. It was made to the same dimensions as copper pipe, and was used during WWII as a substitute for copper. Plumbers don't like it because it's hard to solder. It's not as corrosion resistant as real stainless, so you can't use it in applications that require stainless. I wonder if it could be purchased cheaply enough to be interesting. Perhaps there are other stashes of it around the country.

 

[Eric Johnson]

You'd probably want to sandblast and then carefully paint the radiators. Around here they go for about $100 each, if you have to buy them. Often they can be had for the asking or the hauling. You could even use old steam rads (no top pipes) if you mounted them upside down (to vent). I'm thinking some sort of rack with one on the bottom and another one on the top. Piped separately. Any idea how you'd size them, nofossil? Or just go for the max. I'd think the oxy level in the tank over time would get pretty low.

 

[leaddog]

I'm using two heat exchangers in my tank. The bottem one is 1-1/2 in pipe and there is about 45 ft going back and forth on the bottem. It is feed from the boiler and returns to the bottem of the boiler. There is a bypass valve between the two that I can open to just circulate back to the boiler on a cold start.
On the top I have 45ft of 1/2in fined stainless tubing that is manifolded togeather. That is in the loop to the house. I also have the top connected to the boiler with a line that I can turn on and off.
I have a pump that circulates. the boiler water and I have a pump that circulates the water to the house. The house pump runs all the time as it heats my dhw and hot tub. When the house thermostat calls for heat A three way valve opens and circulates water into the heating loop of the house.
I have found that when I'm running the boiler I leave both exchangers open and run heat to the top and the bottem. When I'm out of fuel the top exchanger keeps the flow to the house. the water will stratify so I pull the heat from the top. It seems to work except when I get close to the high temp the boiler will cycle some at the end. But this is wwhen the outside temp is 70 and 80 and I'm not using ANY heat to heat the house except dhw and hot tub. I may have to add more heat exchanger but I'm waiting to see when it gets cold.

The reason I used pipe was that I had alot of pipe and fittings so they were free.

If I had all that 1in copper I would take 100ft and make a top and 100ft and make a bottem and pipe it up the way I did.

leaddog

 

[Nofossil]

I'm using two heat exchangers in my tank. The bottem one is 1-1/2 in pipe and there is about 45 ft going back and forth on the bottem. It is feed from the boiler and returns to the bottem of the boiler. There is a bypass valve between the two that I can open to just circulate back to the boiler on a cold start.
On the top I have 45ft of 1/2in fined stainless tubing that is manifolded togeather. That is in the loop to the house. I also have the top connected to the boiler with a line that I can turn on and off.

Finned stainless - I am jealous beyond words! Sounds like your system is giving mine a run for the money in terms of complexity. You're the first person besides myself that I've heard of plumbing the hot tub as another hot water zone. Great idea - electricity just seems so wrong. Love to sit in the hot tub when it's below zero and bask in the heat of the wood we cut the year before.

 

[Nofossil]

You'd probably want to sandblast and then carefully paint the radiators. Around here they go for about $100 each, if you have to buy them. Often they can be had for the asking or the hauling. You could even use old steam rads (no top pipes) if you mounted them upside down (to vent). I'm thinking some sort of rack with one on the bottom and another one on the top. Piped separately. Any idea how you'd size them, nofossil? Or just go for the max. I'd think the oxy level in the tank over time would get pretty low.

Being an engineer, I'd have to try and do the calculations. The spreadsheet that I sent you has a place for a heat transfer coefficient. I'd find the value for iron (probably not very different than copper) and make an rough calculation of surface area. Of course, at the end of the day, too much is never enough. If I found a pile of them for free, I'd pack them in. Forget a rack - just pile them on top of each other.

 

[hkobus]

Very timely post. I'm just working on designing my heat storage. My main question is how to calculate the amount of tubing needed to get the right amount of heat transferred. The boiler works well now but with the current temps here it has to cycle too much and the house gets to hot. Any help would be greatly appreciated.

Henk.

 

[Eric Johnson]

Welcome to Hearth.com and our new Boiler Room, hogstroker. That 40 is a nice boiler. I'm going to try your suggestion of blocking off one nozzle on the 60 and see what happens, just for kicks.

I'm committed to building a copper heat exchanger out of 1" and 1/2-inch Type M copper tubing. I have the 1" on hand (100 feet) and I'm going to buy 200 feet of 1/2-inch, which is only $1.15 per foot, so it won't break the bank. Then I'm going to drill and solder up a header-type hx. Two, actually--one to stash heat the other one to recover it. I should have it up and running within a month. So I'll let you know how that works out. I'll post some pics of the progress once I get started building it. I talked to a lot of people and came up with what I think is a pretty good design. Time will tell. I don't want to put all that work into the tank and have a half-assed heat exchanger.

It's a great boiler--really a revelation after using conventional wood boilers for the past 15 years. Frustrating that we haven't had cooler temps, and my storage isn't ready, so I haven't been able to open 'er up and see what she'll do. But I have a pretty good idea.

This weekend I'm going to tie up some loose ends on the tank itself, then hook a big old cast iron radiator up in the greenhouse. I have 24 feet of baseboard in there now that won't cut it in the cold weather. But once that rad is in there, I'll be able to dump some heat in a hurry. Then I guess I'll have to get some plants going.

 

[Rhone]

Sometimes in solar applications with huge tanks is to submerge a small tank in the larger one for the heat exchanger. You could get a stainless tank and submerge it and have that be your heat exchanger. The problem though, a buddy of mine at work had that setup and the small tank constantly developed pinhole leaks which would eventually overfill the big tank and start flooding his basement. To fix, the big tank had to be drained, then another pinhole leak would pop up somewhere else several months down teh road and cause the big tank to flood again and the process repeat.

 

[keyman512us]

The other day I got a quote for a retail copper coil heat exchanger for my tank, just to put things into perspective as I still struggle to decide what to do. This helped: $3,500.

I called my local HVAC supply house, and their price (I assume retail) for 1" soft copper was $5.50 per foot, minimum 60 feet, plus sales tax (9% around here).

One-inch pex-al-pex (no minimum) goes for $1.40 per foot, plus shipping.

The best estimate for replacing copper with pex-al-pex is 3X as much pex to equal the heat transfer of copper.

On paper, I would need about 200 feet of copper coil do do the job, or 600 feet of pex-al, but I think I could get by with less of each.

Something to ponder over the winter as I play around with the much cheaper flat plate heat exchanger option.

Eric,
I would grab a six pack and try the cast iron radiator idea you originally suggested... Didn't you say you had one kicking around anyway???

 

[Eric Johnson]

Hey keyman, good to see you! I was wondering where you wandered off to.

Actually, I just loaded two nice ones into the truck bed. But they're for heating the greenhouse. It's piped direct with water going through 24 feet of finned baseboard now, but the plan is to add the extra radiant and make a glycol loop with my flat plate heat exchanger so that I don't have to haul any more old ci rads off to the scrap yard. The PO froze a couple up years ago, and my wife wasn't buying my observation that they make nice heat sinks and plant stands. $50 in scrap, but I hated to do it, even if they were full of holes. I had to break the big one up just to move it.

This tank is getting a home-made copper hx, a la the header design shown here. But tell you what, when I get my second tank (1,500 gal) commissioned next summer, I think I'll try a couple of cast iron rads.

 

[Rhone]

I love studying solder joints. It's so interesting how much they can tell about the person who made them. Plumbers heat the spot knowing the solder will travel towards the hottest part so they mainly heat the middle area. They use just enough flux to get the job done, excess can cause the joint to fail pre-mature or cause the solder to go to places you don't want. Plumbers use a rule that, 1/2" copper pipe requires 1/2" solder. 1" pipe needs 1" solder. They put their torch to the joint until the flame on the other end turns green, that's the sign it's ready to solder. Until it turns green, the solder will fail. Also, it prevents you from burning it.

Inexperienced homeowners use tons of solder, don't know you heat the place you want the solder to suck to, they often heat the whole joint which causes the solder to spread all over the place. They often have solder icicles, don't know you're supposed to clean the joint following so leave it messy, and don't know how to tell when it's ready to solder so they often keep the flame on too long and burn it.

Homeowners with more practice don't have the icicles, often don't clean the joint following, and have excess solder.

Advanced homeowners have pretty much the same result as plumbers, but will use a little more solder than necessary just to be on the safe side it's their own house after all.

Plumbers have perfect solder joints, no burns, clean, no excess solder.

I rate you advanced homeowner or plumber. Darn good solder job in my book, so glad to see you cleaned it up afterward and you got it sucked in perfectly to the inside. A+++

 

[Eric Johnson]

Thank you, Rhone. Good to see you back here. Heck, good to see you in our new Boiler Room.

This design is based on a solar collector I saw in Mexico a few years ago. It had 3/4-inch headers and 3/8-inch rigid copper feeders. Don't know where they got the rigid 3/8-inch copper, as I've never seen it around here. A heating pro told me to use silver solder for a strong joint. This is just a test run with regular solder, but the real deal with be done right.

Right on about the flux. Just enough is all you need. I usually wipe the joints and clean up with steel wool. Makes for a nice looking connection. Another thing most people don't do is ream the pipe before making the connection. This is almost preferable to regular fittings because you can inspect your work. A regular fitting might look fine, but have a weak channel plugged up with a thin membrane of solder, a piece of flux or some crap that's holding the water back. After a few heating cycles, they start to leak. Don't need that with an in-tank hx.

I'll post some pics when I start producing the units (6 4x5 sections). Should be fun.

You may have heard the old joke about too much solder: "Left some for the next guy." I started soldering years ago when we bought our first house because I didn't want to pay some guy $35 (probably a lot more now) to something that I ought to be able to do. One thing led to another and the next thing you know, I'm doing annual "upgrades" to our heating and plumbing systems. Usually in the dead of winter on Sunday night. More exciting that way, and you become pretty resourceful on occasion.

 

[drizler]

Copper, I remember copper. They used to use it for all sorts of stuff, all gone now into the sands of time.................... Now all we have realistically is plastic for better or worse. Not that its really worse for many things, quite the contrary but you could make so many things out of copper tubing and line that is just too much $$$ now. Ah well

 

[Eric Johnson]

Today I decided to buy a drill press, since I have to drill at least 128 holes in the 1" copper. Plus, I've always wanted a drill press.

 

[mkeefer]

Hi All, I was just searching online for info on heat exchangers and I found this thread - what a relief! I have lived with a primitive outdoor wood boiler for 7 years and like it a lot except for all the smoke it shares. This year I built a new building for my office and shop (I'm an environmental consultant who is home based). Below the slab in the new shack I burried a 750 gal concrete tank and superinsulated it - I'm hoping the ODWB will burn cleaner with the heat storage till I can afford a gassification boiler. I'm now at the point of tyeing the system together so I can heat the building and heat storage tank and am shocked by the cost of copper.The access to the tank is 26" so I don't imagine there are many old radiators that would fit through that opening.

I've played with the idea of KiTec or other plastic piping and like the reduced costs; however, I don't detect much confidence it its abilities. I am now searching out options for pre-made copper coil heat exchangers and would be interested in your findings.

The only pre-made model I have found is at (broken link removed to http://www.stsscoinc.com/Products_HeatExchangerCoil.aspx) - these units are costing in at $885 USD for a 180' 1" coil, a grand sum but not a lot more than the price of 1" copper pipe in Canada.

I look forward to your input.

 

[Nofossil]

Hi All, I was just searching online for info on heat exchangers and I found this thread - what a relief! I have lived with a primitive outdoor wood boiler for 7 years and like it a lot except for all the smoke it shares. This year I built a new building for my office and shop (I'm an environmental consultant who is home based). Below the slab in the new shack I burried a 750 gal concrete tank and superinsulated it - I'm hoping the ODWB will burn cleaner with the heat storage till I can afford a gassification boiler. I'm now at the point of tyeing the system together so I can heat the building and heat storage tank and am shocked by the cost of copper.The access to the tank is 26" so I don't imagine there are many old radiators that would fit through that opening.

I've played with the idea of KiTec or other plastic piping and like the reduced costs; however, I don't detect much confidence it its abilities. I am now searching out options for pre-made copper coil heat exchangers and would be interested in your findings.

The only pre-made model I have found is at (broken link removed to http://www.stsscoinc.com/Products_HeatExchangerCoil.aspx) - these units are costing in at $885 USD for a 180' 1" coil, a grand sum but not a lot more than the price of 1" copper pipe in Canada.

I look forward to your input.

Get to know your local scrapyards and metal recycling facilities. Scrap stainless is worth less than copper(!)

A lot of industrial equipment has finned stainless heat exchanger tubing - hard to do better. I've also toyed with the idea of submersing automotive radiators. They can be had really cheap from your local junkyard - explain that you don't care about what make/model - just take whatever they're about to crush.

 

[Chris Hoskin]

Hi all, interesting thread. Just wanted to mention that it strikes me that all of the submerged heat exchangers (and your flatplate, Eric) seem quite undersized. For example, we would specify THREE of the 180' STSS coils to be used with a 60kW boiler like Eric's EKO or our Solo Plus 60. Remember, you are sizing the heat exchanger to the boiler output, not the heating demand of the house. I have not personally done the calcs, but I know the sizing is based on the difficulty of heat exchange into a tank when boiler and tank temps are close to one another (low Delta T). Coils should be plumbed in parallel, not series, by the way.

As you can see by the cost of these coils, there is good reason to consider having one set of coils act as both charging coils and discharging coils as shown in our drawings ("Square Tank", for example). A bit more complicated on the controls side, but saves the cost of a second set of coils and allows you to send heat straight to the zones if tank temps are down. In other words, the heat from the wood boiler doesn't have to go 'through' the tank to get to the zones, so you don't have to wait for tank temp to come up before you can get usable heat to the zones.

hope this is helpful

 

[Ryedale]

Hi all, interesting thread. Just wanted to mention that it strikes me that all of the submerged heat exchangers (and your flatplate, Eric) seem quite undersized. For example, we would specify THREE of the 180' STSS coils to be used with a 60kW boiler like Eric's EKO or our Solo Plus 60. Remember, you are sizing the heat exchanger to the boiler output, not the heating demand of the house. I have not personally done the calcs, but I know the sizing is based on the difficulty of heat exchange into a tank when boiler and tank temps are close to one another (low Delta T). Coils should be plumbed in parallel, not series, by the way.

As you can see by the cost of these coils, there is good reason to consider having one set of coils act as both charging coils and discharging coils as shown in our drawings ("Square Tank", for example). A bit more complicated on the controls side, but saves the cost of a second set of coils and allows you to send heat straight to the zones if tank temps are down. In other words, the heat from the wood boiler doesn't have to go 'through' the tank to get to the zones, so you don't have to wait for tank temp to come up before you can get usable heat to the zones.

hope this is helpful

Thanks... Do you have a link to the "Square Tank" arrangement you mentioned?