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Community and Q&A

Hot Water in PH (passive house)

Steven Landau | Posted in PassivHaus on

I am designing a PH as a vacation house in Vermont. We will have a peak load of 10 persons over the weekend.

This is a lot of hot water.

Can anyone point me to a Wood Stove/Hot Water heater with:

Outside Air Intake
Hot Water Coils
Oven
Cooktop

in Modern Design with a large percentage of heat going to the water?

Like this:
http://www.wodtke.com/momo.html (hw only)
http://www.euroflues.com/products/fireplaces/woodstove/pallas-back (cooking & oven)
http://www.twlag.ch/index.php?option=com_content&task=view&id=51&Itemid=78&lang=en (hw only)
http://www.edilkamin.it/en/it/termostufe_a_legna/stufa_a_legna_warm_scaldavivande.aspx (food warmer + water)

http://www.esse.com/stoves/multifuel_wood/ironheart.html
(does all but no outside air intake)

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Replies

  1. User avatar GBA Editor
    Martin Holladay | | #1

    Steven,
    I don't have answers to all of your questions. However, I'll do my best to suggest ways of heating domestic hot water using wood fuel.

    1. One option is to insert a stainless-steel water coil in the firebox of a conventional wood stove. There are two ways to do this: (a) with or (b) without the approval of the manufacturer of the wood stove. Either way works, although there is a risk that you might violate the terms of the manufacturer's warranty if you choose option (b). A hot-water coil can be hooked up to a second-floor water tank, creating a passive thermosyphon loop that requires no electricity. Be sure you understand plumbing and PT relief valves before installing your system, though, or the loop can explode.

    The Thermo-Bilt stainless steel coil for wood stoves is manufactured by Hilkoil (www.hilkoil.com). Another coil manufacturer is the Hot Rod from Alpha America (http://yukon-eagle.com/FURNACES/THEHOTRODWATERHEATER/tabid/61/Default.aspx).

    2. You can replace a section of your stovepipe with a Fluemiser -- a section of double-wall stainless-steel pipe that produces hot water. The Fluemiser is manufactured by Hamco Tank Systems (www.fluemiser.com). This will not produce as much hot water as a firebox coil.

    3. Lehman Hardware sells a steel wood-fired water heater (http://www.lehmans.com/store/Stoves___Cook_Stoves___Hot_Water_From_Your_Stove___Hot_Water___System_Two___26845?Args=).

    4. As your probably know, wood-fired boilers (for example, the H.S. Tarm from Denmark -- http://www.woodboilers.com) can be used for both space heating and hot water.

    If you have access to a good library, you can learn more about these options by looking up an article on the topic in the June 2006 issue of Energy Design Update.

  2. Riversong | | #2

    Steven,

    You're on the right track to find a quality manufactured unit that does all you seek (if such is available).

    I would strongly caution against installing an aftermarket water coil, either inside the firebox or in the exhaust flue of an existing woodstove, particularly an EPA-certified unit. They are meticulously designed for optimum clean burn with preheated combustion air, flue-gas circulation and secondary burning. Anything which alters that will reduce the stove's efficiency and potentially increase the condensation (creosote) potential with resultant chimney fire potential (this is particularly true of flue-pipe water jackets which cool exhaust gasses).

  3. User avatar GBA Editor
    Martin Holladay | | #3

    Robert and Steven,
    Concerning the possibility that hot-water coils can increase creosote buildup: here's what I wrote on the topic in the June 2006 article in Energy Design Update:

    "Some critics claim that, since a water coil lowers the temperature of the firebox, it can reduce the wood stove’s efficiency and increase the rate of creosote formation on the walls of the flue. Yet many users of firebox water coils have enjoyed years of trouble-free operation. According to Dave Tjosvold, the owner of Alpha America, the manufacturer of the Hot Rod, “We’ve never heard of any problems due to creosote.” Murray’s experience has been similar to that of Tjosvold. “The coil does take heat away from the firebox, but the amount of heat is very marginal,” says Murray. “It does not create any creosote problem, and it does not lower the stove’s efficiency.” "

    I installed a stainless-steel coil in the firebox of my wood stove in 1992, and have used it all winter, every winter, for the past 17 years. I have no problems with creosote. I clean my chimney once a year.

    Moreover, several wood stove manufacturers recommend the use of hot-water coils. Another quote from the article:
    “[Some] stove manufacturers offer water coils as an option. According to [Thermo-Bilt manager Adam] Murray, “Keystone Manufacturing and Alaska Stove Company in Pennsylvania will predrill their stoves at the factory to accommodate a Hilkoil. We sell coils to just about every stove manufacturer, including Harman Stoves and US Stove.” ”

  4. Riversong | | #4

    From the DOE (by way of chimneysweeponline.com/hocoils.htm):

    "Although it may be physically possible to retrofit some woodstoves with a water heat exchanger, it is not advisable for certain types of stoves. EPA-approved wood-burning appliances are sophisticated in design, and a "do-it-yourself" retrofit may negatively affect their performance. Woodstoves with catalytic converters ("cats") require high temperatures to protect the catalyst from sooting up and losing their ability to work effectively. Non-catalytic woodstoves rely on a high temperature in the firebox for efficient and clean combustion. A hot water heat exchanger placed inside the stove can lower the temperature so far that it might reduce combustion efficiency and thus increase the amount of smoke produced. In any case, all of the manufacturers of woodstoves will void your warranty if you make such changes or alterations."

    While a flue-mounted coil will not effect firebox temperatures, it will lower the flue temperature and reduce the draft, which can have a deleterious effect in a marginal chimney.

    I recently responded to a chimney fire caused by heavy creosote buildup from a large (non-EPA) woodstove with water coil (they claimed they clean the chimney annually).

  5. User avatar GBA Editor
    Martin Holladay | | #5

    Robert,
    Well, if some EPA wood stoves are so finicky that they can't handle a hot water coil, I blame the wood stove engineers. That's reason enough for me to avoid that particular model of wood stove.

    As my article makes clear, plenty of wood stove manufacturers produce wood stoves that can handle hot water coils. If you want your wood stove to produce hot water, those are the models to buy.

  6. Riversong | | #6

    Martin,

    Can you name one EPA-certified woodstove that has a water coil option? All the wood-burning websites I've found claim that they don't exist.

    It's not that those stoves are "finicky", it's that they are highly engineered. For the same reason, you wouldn't install aftermarket "improvements" in a highly-engineered car engine without risking altering the carefully-programmed balance of the combustion system.

    Wood cookstoves are exempt from EPA emissions standards, and they often include hot water coils.

  7. User avatar GBA Editor
    Martin Holladay | | #7

    Robert,
    There are good reasons why someone might want an EPA-certified wood stove; they are clean burning and good for the environment. You're probably right, however, that these stoves don't allow the use of a hot-water coil.

    I never claimed that hot-water coils should be used in EPA-certified wood stoves, however. If you want to install a hot-water coil in your stove, choose a wood stove where such coils are appropriate. I offer this advice based on my personal experience. If you are burning wood, obtaining hot water from your stove is a great feature.

    A little bit of quick Web surfing reveals that some wood stove manufacturers still recommend (and provide) hot-water coils for use in a wood-stove firebox. One such manufacturer is Nippa Stoves. Here's a link to a Web page offering hot-water coils with Nippa stoves:
    http://www.nippa.com/shopstoveacc.html

    [Later edit: The Vermont Bun Baker can be ordered with a hot water jacket:]
    http://www.vermontwoodstove.com/vermontbunbaker.htm

  8. Steven Landau | | #8

    Well, we had a lot of discussion on wood stoves, but nothing of the class of engineering of the Swiss or German Units. I guess I will have to find a way to import.

  9. Riversong | | #9

    Martin,

    All air-tight wood stoves sold in the US since 1988 (with stricter standards in 1990) are EPA certified. The exceptions are furnaces, masonry stoves and cookstoves.

    You seem to be promoting the use of antique 30% efficient stoves, in order to heat water (which will make them even less efficient), rather than use the modern 70% efficient stoves.

    An external water jacket can be used on any stove, though this is far less efficient in heat transfer than an internal coil. And, of course, a pot of water can be heated on top of most stoves.

    More information is available at: http://www.woodheat.org/dhw/dhw.htm

  10. Glenn | | #10

    Steven Check on the Sedore woodstove. They're built in Canada but recently set up shop in Minn.They are predrilled for coils

  11. Steve Landau | | #11

    I checked Sedore, They don't have outside air intake.

  12. Dwayne | | #12

    Steven On your quest for hot water supply, have you checked out Joseph Lyman's external bolt on boilers. They do not affect your emmisions because they are external. They are sold on e-bay. I have talked to the inventor personally a year ago. Predators Choice Energy Alternatives tries to help consumers with new products and referals.

  13. Lucas Durand - 7A | | #13

    Steve, I'm not sure what the PH standard requires but check out: http://garn.com/content/Products.aspx

  14. STEVEN LANDAU | | #14

    Finally Found it.

    http://www.broseleyfires.com/Contemporary/ThermoRossella-Forno_Woodburning-Boiler-Stove.html

    Now, I need to find a way to buy in Europe and Bring it over. Any European passivhouse fans willing to take shipment and re-ship privately to usa?

  15. Dwayne Ruether | | #15

    Hi. Steven , have you checked out the Joseph Lyman add-on boilers designed for this specific problem. These units are quite interesting and an economical alternative. If you have any questions e-mail me.

  16. Suzanne | | #16

    Has anyone investigated and rated the Pacific Energy Water Coil Option wood stove?

  17. steve | | #17

    I haven't found anything on Joseph Lyman, other than patent applications.
    Pacific Energy stoves don't offer outside air combustion intake.

  18. Dwayne Ruether | | #18

    Hi.Steven . If you go to google and search Joseph Lyman Add-on hotwater boiler watertank it will give you an e-bay site in which the new units are sold. The site has a brochure type add explaining the product. Let me know if you find it. It's worth the time. Also being a designated spokesperson for Sedore Stoves in Saskatchewan Canada I believe you should check those out . I believe in Canada they have an outside air bar for fresh air intake. They are also available with hotwater coils. check it out. Keep in touch.

  19. Dwayne Ruether | | #19

    Hi. Steven this is Dwayne Ruether at Predators Choice Energy Alternatives. I haven't recieved a reply as of March 17/10. I have been thinking about your hot water needs and so I recalled a product I came across on my google travels. Your hot water needs are probably quite substancial, and so depending on your budget you should check out Woodpecker boilers on http://www.woodpecker.com . They have three different products, pellet indoor boiler, pellet outdoor boiler and a indoor wood gasification indoor boiler. Check them out.. Get back to me see what you think.

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