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[aries9245]

I'm about to add a side arm to my hot water tank.. I have a 15" long type with several tubes running on the inside of the HX .. My question is would this type of HX produce enough hot water as opposed to the 3-5 ft ones I'm seeing im suet there is a btu difference. But will it really matter that much ?

[cando attitude]

HI Aries,

Largely its about heat transfer area.  The more heat transfer area you have, the quicker your recovery will be.  Personally, I would opt for the longer ones.  Not only will the longer ones most likely have more heat transfer area, their length will help the water "draft" or pull the colder water from bottom as it rises from being heated (i.e. turning over the water in your tank).  This works much in the same way a longer chimney drafts better than a short one.

In either case, adding a small circulation pump  on the tank side will greatly improve recovery time....if you feel this is a must.  Personally, I hate the idea of added initial cost and Kwh to run it (even though it is tiny).

Cando

[mlappin]

HI Aries,

Largely its about heat transfer area.  The more heat transfer area you have, the quicker your recovery will be.  Personally, I would opt for the longer ones.  Not only will the longer ones most likely have more heat transfer area, their length will help the water "draft" or pull the colder water from bottom as it rises from being heated (i.e. turning over the water in your tank).  This works much in the same way a longer chimney drafts better than a short one.

In either case, adding a small circulation pump  on the tank side will greatly improve recovery time....if you feel this is a must.  Personally, I hate the idea of added initial cost and Kwh to run it (even though it is tiny).

Cando

 

[aries9245]

Ok I agree with not putting a circulator on. Does anybody have a good website to get a HX at a good price.. I've made my own in the past pipe inside another but not sure if this extracts the same btu's as the other I've seen with many smaller pipes inside..

[juddspaintballs]

I've often wondered about using those stainless steel pool/hot tub heat exchangers for a water heater.  They're shorter but have more tubes inside for more heat transfer surface area.  I hadn't thought about the length not thermosiphoning well.  I think this house, I'll do a long copper sidearm for thermosiphoning and keeping the tank warm and a 10 plate exchanger after the water heater tank for on-demand hot water. 

As for long copper sidearms, I bought my last one from Anderson's Outdoor Wood Furnace (http://www.freeheat4u.com/) through eBay, I believe.  I also got my 22x22 water/air heat exchanger from them.  I have no complaints with their products or service.  There are other sellers out there, however, if you choose not to use Anderson's.

[mlappin]

I seen one that had a spiral wrapped around the inner pipe so the water had to circulate around the inner all the way to the top.

Found it: http://www.altheatsupply.com/side-arm-heat-exchanger-34.html

Unfortunately only has 3/4" ports.

[juddspaintballs]

I know the Anderson's side arm is "rolled" to help turbulate the water inside.  How well it works, who knows.  It isn't soldered together, though, so it would be easy to braze a piece of copper wire to it before assembling it if someone were so inclined.

[willieG]

some can make their own coil in a shell...I have scrounged the outer pipe and just had to buy the copper coil and the fittings...I ended up with 50 foot 1/2 coil inside a 12 inch pipe about 22 inches long....endless hot water for under 100 bucks...and no (or very little) added head pressure

[aries9245]

Thanks guys I'll ck them out! Willie how did you make yours I've made tube inside bigger tube before but never coil type

[LittleJohn]

I have made a Tube inside Tube before also...  not so much fun to prep and solder up, but once install nearly endless hot water!!!