# Homemade spiral heat exchanger?



## jimnorth (Jan 28, 2008)

I was looking at the spiral tube copper heat exchangers sold by TARM / STSS for use in their heat storage tanks.  Judging only by the pictures, it seems making one of these is doable for someone with experience sweating copper.    Has anyone ever attempted to do this?   Is there more to these than meets the eye?

Thanks,
Jim

.... forever looking to save $$$


----------



## Eric Johnson (Jan 28, 2008)

They're just regular copper coils. Not much sweating involved, other than the connections. However these days, "save $$$" and "copper" don't belong in the same sentence.


----------



## jimnorth (Jan 28, 2008)

I know copper is expensive, but I was just quoted $935 for a 180 foot DHW coil from the rep at HS TARM.   Last I checked, copper tubing wasn't quite that expensive.  Maybe I should check again?


----------



## Eric Johnson (Jan 28, 2008)

Last time I checked, last fall, 1" soft copper tube (I believe it was Type M) was $5.50 per foot. I bet 3/4 is close to $3.

Four years ago I paid $1 a foot for 1" Type M rigid copper. Now it goes for around 3 times that.


----------



## Bob Rohr (Jan 28, 2008)

I believe this tank and coil is what you are looking for.  www.stsscoinc.com.

Consider a few shorter loops headered together.  Like two 1" header pipes with four 50 foot coils of 1/2" copper.  Similar to how a solar panel is built.  Or the way Thermomax and Ergomax build their indirect tanks.  That should bring the cost down, flow just as well a one 180' loop and actually have better heat exchange.

 hr


----------



## wsurfer49 (Jan 28, 2008)

I have not priced copper lately either.  I had planned on trying to make my own coils though and may still.  Will have to see how much the manufactured runs vs the price of the pipe.

I found a few books on the subject a few years ago and the way they described making the coil was to fill the tubing with sand and seal off the ends, the sand will prevent the copper from kinking.  Sounds like a good idea to me.  

Rob


----------



## bbb123 (Jan 28, 2008)

Mine has 2 180' x 3/4" for HX and one for DH.  As far as DIY there is nothing to them just bend them around something solder ends and 3 or 4  1/2 inch supports up middle.


----------



## jimnorth (Jan 28, 2008)

bbb123 said:
			
		

> Mine has 2 180' x 3/4" for HX and one for DH.  As far as DIY there is nothing to them just bend them around something solder ends and 3 or 4  1/2 inch supports up middle.




Did you make you own coils, or buy them with the tank?


----------



## bbb123 (Jan 29, 2008)

They came with the tank from Tarm I would have made them if I had known what they were.  Heat storage was a foreign language to me 2 years ago (no hearth.com/boilerroom).  Knowing what I know now I would build a tank and HX (wish I put solar in to).  If I remember the copper coils were not alot more than the going copper price so it wasn't that big of deal.


----------



## Bob Rohr (Jan 29, 2008)

Skip the sand, save it for the kids sandbox, or liter box   You really don't want any residual sand in your pumps or components.  Soft copper will easily bend around a barrel or drum for instance.

Actually it comes in a nice coil.  Just pull it apart and make some brackets to hold the spacing you want.

 hr


----------



## mikeyny (Jan 29, 2008)

Master of Sparks,

                        DITTO,

                        That's just too easy.


----------



## Nofossil (Jan 29, 2008)

I just made a wooden form and bent it around that. I used 4 pieces of 1/2" type M as vertical supports. I attached the verticals by lashing with copper wire and soldering.


----------



## Tarmsolo60 (Jan 30, 2008)

nofossil said:
			
		

> I just made a wooden form and bent it around that. I used 4 pieces of 1/2" type M as vertical supports. I attached the verticals by lashing with copper wire and soldering.



Same thing i did pretty much, 22" diameter is what the coils are as per tarm, I used 3 pieces of 3/4 L for vertical supports and utilised one of them to feed the bottom of the coil. Pretty easy to make.


----------



## WRVERMONT (Jan 30, 2008)

I made a wood form and wrapped copper around them.  Worked really well!  Just a note about spiral coils.  If there is enough space in your tank, make more coils (piped in parallel) each having a shorter length. The same heat transfer can be accomplished with less head pressure.  Better heat exchange efficiency.  You can also put one coil within another to save space.  For example you could make three 60' 3/4" soft copper coils that nest together then pipe them parallel to each other.  You end up with a higher flow exchanger.   The real challenge for these exchangers is the PRICE OF COPPER!


----------



## drizler (Jan 30, 2008)

I think the price of copper has come down some lately.  A couple years I was marveling at the cost of a stick of 3/4 copper at Lowes for around 22 and tax.   I saw it was down to something in the neighborhood of 18 bucks.    Still sucks .


----------



## cguida (Jan 31, 2008)

Does anyone have any thoughts about the trade-offs between copper coils and flat plate heat exchangers?

SSTS reports that their 120 foot coil costs about $660, and the 180 foot coil costs about $830.  They recommend two coils, plus shipping.

So it adds up pretty fast.

On the other hand, a 12x5inch 40 plate heat exchanger on ebay costs about 270, including shipping. 

That is a pretty compelling cost difference.  So why do people still use copper?  What am I missing?


----------



## drizler (Jan 31, 2008)

I just swung by Lowes last night and its now $16 and some change for a stick,  definitely coming down.


----------



## Eric Johnson (Jan 31, 2008)

Smee said:
			
		

> Does anyone have any thoughts about the trade-offs between copper coils and flat plate heat exchangers?
> 
> SSTS reports that their 120 foot coil costs about $660, and the 180 foot coil costs about $830.  They recommend two coils, plus shipping.
> 
> ...



There are some interesting discussions here about using a flat plate heat exchanger instead of a coil or some other in-tank hx. Basically, you need to pump water through both sides of a flat plate, and then you have to pipe the tank so that you can both store and recover heat when you need to. It's easier with an in-tank hx but the price differential is, as you point out, a compelling consideration. Search "flat plate" and you'll find the threads I'm talking about.


----------



## SteveJ (Feb 3, 2008)

I think the main advantages of copper coils over flat plate heat exchangers in storage applications are:
1. Heat stratification - see https://www.hearth.com/econtent/index.php/forums/viewthread/13844/
2. No additional pump required on the storage side - important for thos of us off-grid!!

As Eric points out there are several discussions on the flat plate versus copper coils - search on storage, stratification to get an idea.

Others can elaborate more.

Hope this helps


----------



## chuck172 (Jun 1, 2008)

Looking into building my own copper coil HX's coils. Current STSS price is $1,150.00 per 180' . Need 3. I can buy 100' type L copper coils for $300.00
Totals:
STSS-  $3,450.00
540' copper- $1,650.00
Same material, Doesn't seem very hard to do.
I'd like to hear some success stories here:


----------



## DaveBP (Jun 2, 2008)

I'm going to be building my own heat storage tank to go with my  Tarm 40 (picking it up next week) and would like to build my own heat exchangers if I decide the copper coils are the way to go. STSS's markup seems pretty steep for the sort of work required. Comparing prices at CopperTubingSales.com it looks like a nearly 100% margin. I spoke to the owner at STSS about a year ago and he indicated that 3/4 dia. is the most effective compromise between friction, exchange surface per foot and cost of material. The tables I've looked at make me think he was being pretty candid about that. They have done a lot of research and serious testing over the years. One question I have is what are the trade-offs between the different grades of tubing in this kind of application. Refrigeration tubing is 25% thinner wall for 40% less cost (.045/.035,$300/$180). It's rated for 260 lbs. pressure at 400 F. That sure ought to be adequate. What I don't know from experience is how you solder it together. Standard fittings don't work on it because of the different O.D. Is it trickier to work with for those of us who don't have surgeon's fine touch? Flat plates are really cool looking but they require another circulator and a reversible one at that to use the same HX  to extract the heat from storage and I haven't yet seen a definitive answer on how big they need to be. My intuition is that the fittings to and from the HX should be the same size as the pipe from the boiler, 1 1/4 in my case. Flat plate HXs that size aren't so cheap, even on Ebay. I like the simplicity of the copper coils, but I sure would like to spend as little as possible on precious metals. Anybody out there with experience working with the different tubings? Is type 'L' worth the extra cost? For my first post I've rambled a bit, haven't I?


----------



## NHFarmer (Jun 2, 2008)

Dave, Welcome, I am also looking to have my Tarm Solo40,delivered next week.Also building my own storage,7' diam,1000 gal.I have been going between flat plates and coils.I haven't decided yet but the refrigeration tubing sounds interesting,sorry I can't offer any working experience but I am sure someone will.


----------



## Chris S (Jun 2, 2008)

L tubing is a thicker wall than M , and usually easy to find in rolls which would very quickly become... your coil.

How about looking for some actual coils from discarded idirect water heaters, and using them?  A good percentage of the time- the tank leaks but the coil Is sill good.
we usually sell them for scrap.... maybe  a business venture is available here


----------



## chuck172 (Jun 2, 2008)

STSS uses L copper. I think I'd like to have that thickness. Pinholes can be a big problem that can occur if the water in the tank isn't properly conditioned. (acidic?)

I understand STSS uses 20" diameter coils at 43" high. I wonder if they use any type of stand or just sit them on their tank liner. They also have a way that automatically bleeds the coils of air.
Uncoil the 100' type L copper to 20" dia. Using a coupling  or a swage tool to connect and come out to 180' Spreading out the coil vertically to 43" soldering straight copper tubing as stiffiners. 
Sounds like a plan.


----------



## jebatty (Jun 2, 2008)

I remain puzzled over the fascination with large (STSS style) coil hx's when the low relative price and high efficiency of plate hx's is so well known. Without repeating my prior posts on this topic, all I will add is that the cost of an extra circ pump appears to be the primary objection. Addressing that objection:

1) Plate hx on ebay about $225.
2) Taco 007 on ebay about $50.
3) Elec draw of 007 is about 85 watts. Assuming 6 hrs/day, which for my extreme northern clime and heating 1000 gal of storage would be average (some days longer, some shorter), that amounts to 15kwh/mo, or $1.40/mo at our $0.09 rate.

Chuck172 reports cost of copper (I assume 3/4", which I think is STSS) to make your own coils to duplicate STSS: 540’ copper- $1,650.00.

The math: $1650 - $225 - $50 = $1375 / $1.40 = 982 mos = 8.5 years of operation before payback on coils for my installation. If I take that $1375 and invest it at 3% (on average can do much better than this), that is $41.25/hr, and my electric cost (generous) is $1.40 x 6 = $8.40 per year (six months of heating).

Simplicity and time: a plate hx over making coils is no contest. 

Seems to be that the cost and operation of an extra circ pump as an objection to the plate hx is based on erroneous assumptions.


----------



## free75degrees (Jun 2, 2008)

Does anybody think that the amount of coil that STSS recommends is overkill?  540' of 3/4" copper gives about 15,000 square inches of copper surface area.  In another post somebody said that about 4000 square inches was needed for an eko 40.  I hope it is overkill because I am planning on using 5600 square inches (3 section of coil in parallel, each one is 100 feet of 1/2" copper).

Assuming the STSS numbers are overkill then the cost comparison is closer.  I am already committed to copper since I have already bought and coiled a bunch of it, but if I was starting over, I might go with a flat plate.  I will have spent about $500 for all of my copper, including fittings, so I am about twice the cost of flat plate.


----------



## bbb123 (Jun 2, 2008)

free75degrees said:
			
		

> Does anybody think that the amount of coil that STSS recommends is overkill?  540' of 3/4" copper gives about 15,000 square inches of copper surface area.  In another post somebody said that about 4000 square inches was needed for an eko 40.  I hope it is overkill because I am planning on using 5600 square inches (3 section of coil in parallel, each one is 100 feet of 1/2" copper).
> 
> Assuming the STSS numbers are overkill then the cost comparison is closer.  I am already committed to copper since I have already bought and coiled a bunch of it, but if I was starting over, I might go with a flat plate.  I will have spent about $500 for all of my copper, including fittings, so I am about twice the cost of flat plate.



I have the Tarm, STSS setup your saying 540'.  It's 360' for the HX for boiler and 180' for domestic hot water.  Mine handles any heat the boiler makes with no idle.  You should check NoFossils site I think he says how much he put in and he gets some idling.  I wouldn't short the heat exchange one reason for storage is to keep boiler from idling.


----------



## free75degrees (Jun 2, 2008)

bbb123 said:
			
		

> I have the Tarm, STSS setup your saying 540'.  It's 360' for the HX for boiler and 180' for domestic hot water.  Mine handles any heat the boiler makes with no idle.  You should check NoFossils site I think he says how much he put in and he gets some idling.  I wouldn't short the heat exchange one reason for storage is to keep boiler from idling.



I see, so I should compare to the 360' feet from stss rather than the 540'.  360' gives about 10,000 sq inches.

I checked nofossil's site, and it looks like there is roughly 100 feet total of 3/4" copper for the boiler, which comes out to about 2,800 sq inches.

Nofossil - how much idling do you get?  I looked at your example chart and I didn't see anything that looked like idling, in fact it looks like the opposite - i.e. you tank circulators shut of periodically because the boiler water is getting too cool, which implies that the HX is taking away more than enough heat.  I am reading this correctly?


----------



## Adios Pantalones (Jun 2, 2008)

I made a heat exchanger (smaller scale) to be used as a "wort chiller" for beer making.  For a 22" spiral, coul around anything round and roughly 22".  You can also get a spring-looking doohickey that slides over the pipe and prevents kinking.

More efficiency, but way more back ressure, would be gained by introducing right angles in the pipe which would create turbulence inside the pipe and bring hotter (or colder, depending on which exchanger) water to the pipe surface.


----------



## chuck172 (Jun 2, 2008)

I'm correct in saying STSS 's coils are 3-180' coils, that is 540'
bb123, How do the coils sit on the floor of the tank? Is there any special support STSS uses?


----------



## Adios Pantalones (Jun 2, 2008)

I looked at their site recently, and they claim that the coils sit unsupported.  They are 22" wide and 43" tall.  I would guess that they are more than rigid enough that the connectors hold them in place.


----------



## bbb123 (Jun 2, 2008)

I don't remember anything on floor but it has been awhile.  There are 3 coils, as far as HX for excess boiler heat there are 2 coils 180' x 3/4".  The third coil in mine is for my domestic hot water.  There is room for a 4th coil which I wish I put in for solar.  I had a (hot) water maker on its own zone from my oil boiler but Tarm recommend removing that and getting domestic from the main tank (3rd coil).  Back awhile ago we were doin efficiantcy tests and Nofossil obviously has precise monitoring equipment.  His boiler was idling at a lower temp. than mine was.  I have mine set up to heat tank up to 180 deg mine (depending on stage of burn) will not idle till it gets up around 170 deg.  Course when I put mine in i think the coils were under $400 each.  I understand the push for flatplate HX with current copper prices.  I just looked at Nofo's tank he has 50' for his domestic, 70' for solar, and his BOILER HX is 50' x3/4 plus 40"x60" square section.  The square section appears to be 3/4 or 1" with 1/2" paralel going between them.  Plus remember if you do figure out how many square inches he has he only has a eko 25 not a 40.


----------



## bbb123 (Jun 2, 2008)

Adios Pantalones said:
			
		

> I looked at their site recently, and they claim that the coils sit unsupported.  They are 22" wide and 43" tall.  I would guess that they are more than rigid enough that the connectors hold them in place.


They are rigid they have 3 or 4 pieces of 1/2 copper up middle for support so the don't slinky on you.


----------



## free75degrees (Jun 2, 2008)

bbb123 said:
			
		

> Plus remember if you do figure out how many square inches he has he only has a eko 25 not a 40.



Yes, mine (with a Tarm 40) needs to be about 65% larger than if I were using an eko 25 (based on relative btu output for eko 25 and tarm 40).  So 2800 sq inches for an eko 85 would convert to about 4600 sq inches for a tarm 40 or eko 40.

If nofossil gets some idling around 170* then I'll want to add some more oomph than 4600 sq in would give.  I only have baseboard heat with 800 gallons of storage so 170* would only give me about 30* of range.  I'd like to get that a bit higher if I can.

Using 1/2 tube I would need 244 feet to get 4600 sq in.  So my plan is to use about 300 feet, which is 23% more nofossil's system scaled to a Tarm 40.  I know this is probably an over simplification, but to do it right I'd probably have to solve some unsolvable differential equations.  If 300 feet is too small I guess I can add another coil later.


----------



## Nofossil (Jun 2, 2008)

I wish I had more coil surface area - I'm actually contemplating forming up some fins from copper flashing and clipping them onto the coils. It works great until the tank top starts getting near 170. Then the coils can't transfer as much heat as the EKO generates, and I go into temporary idling.

When withdrawing heat from the tank in the summer, I have to restrict the flow rate to get out water that's hot enough to be useful.

Bottom line - more surface are is better.


----------



## jebatty (Jun 3, 2008)

Although I use a plate hx to isolate my Tarm from the pressurized storage, with pressurized storage you can eliminate the coils for tank heating and heat the tank directly from the boiler. With the cost of coils compared to the cost of picking up a used LP tank, it seems that more attention to pressurized storage might be worthwhile. A hx would be needed for DHW, and a plate hx here would seem to be a very economical and efficient way to go due to the difficulty of putting any coil in a LP tank.

Space issues come up with large LP storage compared to a STSS or home-made open storage tank.


----------



## Ron Lloyd (Jun 4, 2008)

That’s the route I’m going only I intend to put a copper coil inside the propane tank for DHW. I ordered a 12” flange and gasket no more than two hours ago from here.

http://www.hydro-eng.com/flanges_gaskets.htm

I will have a short section of 12” pipe welded on top of the propane tank and the above flange will be welded to the pipe. I intend to make my own lid (blank flange) from ½” thick steel. I’m going to bore 2 holes in the lid (in addition to the bolt holes) slightly larger than the outside diameter of a ½”x 4” bronze nipple. Then I’ll have those two nipples brazed in those holes. The first fittings on the outside of the lid will be 1/2” unions (for assembly and disassembly purposes) and then I'll transition to PEX for both inlet and outlet. The idea is for the DHW coil to just “hang” from the lid but if it looks like it needs some additional support I will add it. The guy I’m buying the tank from will take care of all the welding and pressure testing.  

Ron


----------



## Adios Pantalones (Jun 4, 2008)

Is a pressurized tank needed for direct tank heating because the outflow is forced by tank pressure?  Could it be done with 2 pumps instead (I know- more power etc- just thinking is all)


----------



## Ron Lloyd (Jun 4, 2008)

I’m not sure I understand your question either. From my understanding this type of system is pressurized because there is a fill valve that keeps the water pressure in the boiler and therefore in the tank relatively constant. There is only one circulator needed to move the heat from the boiler to the tank. Then you can either use one more circulator and a series of zone valves or a series of separate circulators for each zone to move the heat from the tank to the load.

Ron


----------



## Adios Pantalones (Jun 4, 2008)

Ah- got it- it's open circuit to the boiler (derrr- I should have realized that)


----------



## jebatty (Jun 4, 2008)

I am confused by the question and the answers. A pressurized system does not force water by means of the pressure through the system. The whole system is of equal pressure. It is pressurized to remove all air and seal the water in the system. The pump is a circulator, meaning it is neither pushing nor pulling water through the system. It is not creating pressure, it simply moves water through the system by creating a pressure differential. 

An open system is open to the air and is constantly "boiling" or evaporating water out of the system, thus the need to add water, exposure to air, and thus also corrosion issues. These are avoided or greatly alleviated in  a closed, pressurized system. There are other factors involved in a pressurized system. 

Suffice it to say that a single system cannot be both open (non-pressurized) and closed (pressurized) unless they are separated. Else pressure would alway flow to point of less pressure until pressures were equal, and a pressurized system would lose its entire pressure to the unpressurized, open system.
.
I don't know if this helps anything.


----------

