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Old 02-02-2017, 07:16   #1
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Heat exchange from reflek flue

I was wondering if anyone had thought about making a heat exchange unit to heat the calorifier and towel rail . Using soft copper pipe coiled around the flue of a heater because there is such a waste of heat . I realise I would need an expansion tank and some careful planning but it must be possible or shall I carry on dreaming while this gale is blowing !
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Old 02-02-2017, 08:40   #2
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Re: heat exchange from reflek flue

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I was wondering if anyone had thought about making a heat exchange unit to heat the calorifier and towel rail . Using soft copper pipe coiled around the flue of a heater because there is such a waste of heat . I realise I would need an expansion tank and some careful planning but it must be possible or shall I carry on dreaming while this gale is blowing !
Yes, I've been planning it for use on my Sig heater, very similar to the Refleks. I had a soft copper coil in my old boat, in which I also had a Sig. In that installation I had the coil in the firebox and always worried about corrosion of the copper from fuel contaminants.
On this one I'm thinking of doing what you described making a coil that wraps around the flue. I will enclose the coil wrapped flue with a larger diameter flue pipe so that it concentrates the heat. I'm pretty sure it'll work. My chimney flue is 3" so I'm going to use 3/4" copper and a 6" SS flue pipe to enclose the assembly.
The picture is of the heater with the fin radiators I made, which cool the flue pipe by at least 100 degrees F, the heat at the deck head was reduced by 100 + degrees the rest still goes out the chimney. I expect that I'll harvest most of that heat using the water jacketed flue. The trade off is maybe that I'll have run the draft assist fan a bit longer, and, that I'll not have quite so much heat from the chimney fin radiators. But the head compartment and forward compartment will be warmer. I'm not yet sure if there will be enough transfer from the heater coil to heat the water heater (calorifier).
With the coil in the firebox it took a while to to get the convective water flow going or it would boil the water and create a steam lock up, I finally put in a small aquarium water circulator pump that only needed to run for a little while to ensure that the convective flow started properly and then it could be shut down. And yes you will need an expansion tank and a water venting valve at each end of the water piping.
On my old boat I was harvesting enough heat to distribute to radiators I'd installed under the cabin soles and still had plenty going up through the flue. I enclosed that flue pipe with a 12" diameter fiberglass insulation pipe with a 4" diameter tee top and bottom and harvested a huge amount of heat that way. The heat sharing of the insulated flue pipe was so great that it melted the muffin fan I had installed incorrectly on the heat outlet rather then the inlet and almost caught the overhead on fire at the deck iron.
As I write about the old installation I suspect that there would be enough waste heat for the water heater if the coil was long enough and enclosed correctly.
I've also installed a truly excellent down draft cap called the Vacuvent. I can't praise it highly enough since I installed it I've experienced no blow backs and no fire box explosions. (photos below)
Enjoy the dreaming, I've often enjoyed the winter gales snug below with the heater running.
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Old 02-02-2017, 09:02   #3
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Re: heat exchange from reflek flue

it seems we are thinking on similar lines I was worried about water boiling as the flue pipe gets extremely hot that was the thinking of a towel rail and calorifier connections . Pipe runs would be aprox25 foot long to heater this could be extended as required ( underfloor heating] if found to be too hot.im sure this would work on gravity as top of flue would give about 6 foot of head the other thing was how many coils to go around the flue , could be a bit of experimenting. I will have a go in the next couple of months ready for next winter. will keep you informed
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Old 02-02-2017, 15:07   #4
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Re: heat exchange from reflek flue

Do you currently have an engine loop through the water heater? If so there's another thread re: a very simple way to add the coil from the Refleks into that line. Sorry, but I don't remember the thread title but if you do a seach you should find it.
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Old 03-02-2017, 08:04   #5
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Re: Heat exchange from reflek flue

Yes I do have an engine loop to calorifier should be easy to tap into still cant decide how many coils to wind around flue . will try and find other thread
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Old 03-02-2017, 08:35   #6
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Re: Heat exchange from reflek flue

I'm not sure but I think it was a post by Sailorchic that had the description of how to tap into the engine loop safely and easily.

On the old boat I used in 5 turns of 1/2" copper inside the firebox for this one around the flue pipe I think I'll try for 9-11 turns of 3/4" as I have a draft balancing damper 12" above the stove top and I want to stay below that.

I've got a bus heater already plumbed off the engine loop so I'll extend those hoses to heat the forward compartment and head. I think I would want the towel heater to be on the return leg to the heater since the water gets so hot.
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Old 03-02-2017, 10:41   #7
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Re: Heat exchange from reflek flue

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I'm not sure but I think it was a post by Sailorchic that had the description of how to tap into the engine loop safely and easily.

On the old boat I used in 5 turns of 1/2" copper inside the firebox for this one around the flue pipe I think I'll try for 9-11 turns of 3/4" as I have a draft balancing damper 12" above the stove top and I want to stay below that.

I've got a bus heater already plumbed off the engine loop so I'll extend those hoses to heat the forward compartment and head. I think I would want the towel heater to be on the return leg to the heater since the water gets so hot.
I thought I'd posted a photo of the heater on an earlier post but it's not here now so:
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Old 03-02-2017, 10:54   #8
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Re: Heat exchange from reflek flue

Refleks has a diagram and description of how to do exactly what you are describing. It uses tubing wrapped around the chimney pipe and convective circulation of the water, ie no pump required.
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Old 03-02-2017, 10:55   #9
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Re: Heat exchange from reflek flue

Also, if you find you need more thermal conduction between the flue and the copper tubing, silver braze the copper to the flue. This will increase the heat transfer dramatically.
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Old 04-02-2017, 07:38   #10
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Re: Heat exchange from reflek flue

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Refleks has a diagram and description of how to do exactly what you are describing. It uses tubing wrapped around the chimney pipe and convective circulation of the water, ie no pump required.
I found that I would need to pump the water for about twenty minutes or I'd boil it. After that I didn't need to run the pump at all for as long as I was running the heater but for my installation it was necessary. I also needed bleed valves at top ends of the piping runs, and a header tank at the highest point in the system.
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Old 04-02-2017, 08:29   #11
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Re: Heat exchange from reflek flue

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Refleks has a diagram and description of how to do exactly what you are describing. It uses tubing wrapped around the chimney pipe and convective circulation of the water, ie no pump required.
Can you post a link to the diagram of the chimney wrap, I was unable to find it on the site?
Thanks.
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Old 04-02-2017, 10:24   #12
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Re: Heat exchange from reflek flue

i looked on their website and didn't find a chimney coil diagram. I bought a Refleks several years ago and it came with the diagram showing the coil. if I can dig it out I'll scan and post it.

The Refleks website does show a set up for water heating systems using one of their water heaters, for both convective and pumped setups. They spec a minimum rise from the heater of 1" vertical in 20" horizontal for the water line.
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Old 04-02-2017, 14:21   #13
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Re: Heat exchange from reflek flue

Who is the supplier for the VACUVENT draft cap pictured?

Looks very nice.
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Old 05-02-2017, 04:01   #14
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Re: Heat exchange from reflek flue

I'd also like to know the vacuvent supplier should anyone know. I've searched with no luck so far.
Thanks in advance.
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Old 05-02-2017, 09:07   #15
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Re: Heat exchange from reflek flue

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Who is the supplier for the VACUVENT draft cap pictured?

Looks very nice.
My apologies, I had the name wrong it's Vacu-Stack.
I formerly had problems with high winds, 25 to 35 knots, downdrafting and blowing out the flame and then the the hot burner reigniting explosively, there were times when I was fearful the the heater would be damaged by the explosions and I would shut down. Not too happy on cold nor'easter nights.
I tried other solutions: a draft fan, other types of chimney caps: Dickenson "H", and a feather cap that weather cocked. This one cured the problems of a straight down blast of wind. I haven't had a backdraft or flame out since I installed it. I sound like a commercial but I have no connection to the company, but I'm just so happy about finding a solution to a very annoying and possibly dangerous problem.

Wind Resistant Chimney Caps | WoodlandDirect.com: Chimney Caps & Dampers

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