Radiant heating/woodstove

Discussion in 'HVAC Heating & Cooling' started by Supervisor, Feb 28, 2012.

  1. Supervisor

    Supervisor Construction Supervisor

    Messages:
    7
    Location:
    Lunenburg ma
    Hi Guys, Gals,

    Not sure if this is the right place to ask this...(Frickin newbie)-I am a carpenter/construction super that has worked just enough with HVAC pro's to be dangerous, I am looking for some feedback about my latest idea, that is I have just finished installing all of the pex in my basement slab, 36X48, now I am starting to think about the zoning of my first floor and how I am going to run my circuits and I start looking at my hearth where my wood stove is going and I thought....instead of running around the hearth maybe I could run some 3/4" copper tubing through the mud slab of the hearth and help the boiler with the heat load, that being said I do understand that the floor temps that are needed are about 90 degree's for the basement slab and 120 degree's )for the first floor(pex in Extruded plates attached to sub floor with 3/4" hardwood on top), I am not sure of the water temps that I could get back through this "copper loop of radiant" if I assembled it, that being said I also understand that after about 200 degree's things get downright dangerous,=steam Pressure) so obviously safety measures have to be used, but I thought I might ask for thoughts on this project.....anyone......anyone....Bueller.

    Lastly I am working with a Licensed tech for my boiler install, I just hoped to have a better handle on my scope before getting him to price this out. I don't like wasting his time so I can figure things out.



    Thanks Chris
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,319
    Location:
    New England
    Not sure trying to engineer a way to add heat to the water from a wood stove is worth the engineering costs to make it safe. I'm sure you'll get some other opinions.
  3. Hackney plumbing

    Hackney plumbing Homeowner

    Messages:
    1,174
    Location:
    Alabama
    I love this kinda thread. I live in a hot climate but we need heat a few times a year. Anyway I was reading a few nights ago about a kit you can buy that installs inside a woodstove I believe used to heat the water for potable domestic or whatever. cant remembr the name but will try to find it for you.

    I considered building a wood fired boiler and installing a water to air heat exchanger in my duct work. With a gazillion controls to operate it all. LOL
  4. Hackney plumbing

    Hackney plumbing Homeowner

    Messages:
    1,174
    Location:
    Alabama
    Here is the link. I'm not sure if they work or not or if their worth it? Seems like it would be easy enough to build it yourself. Looks like its just bent stainless tube.

    http://www.hilkoil.com/
  5. Dana

    Dana In the trades

    Messages:
    3,028
    Location:
    01609
    He's talking about using the heat from the hearth, not direct from the wood stove. (SFAIK there are no wood-stove boiler hacks kit or otherwise that meet MA code.)

    Simply running PEX in the hearth has no safety consequences. (If the hearth is above 220F it means your house is already on fire, eh?;-) ) But the heat transfer rates won't be ultra-high.

    If you want to run your radiant with wood, there ARE code-compliant high efficiency wood boilers out there. (A buddy of mine just a few miles down the road from you in Ashby is running his radiant heated house off a wood boiler.)
  6. Hackney plumbing

    Hackney plumbing Homeowner

    Messages:
    1,174
    Location:
    Alabama
    Yeah I think taking it from the stove would be better. Maybe they could make it legal. For me personally at my house I can do anything I want,so I may buy one just to play around with.
  7. Hackney plumbing

    Hackney plumbing Homeowner

    Messages:
    1,174
    Location:
    Alabama
    Yeah I think taking it from the stove would be better. Maybe they could make it legal. For me personally at my house I can do anything I want,so I may buy one just to play around with.

    Its listed by the "Energy Testing Laboratory of Maine" Southern Maine Vocational technical institute.
    Last edited: Feb 28, 2012
  8. Dana

    Dana In the trades

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    Location:
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    If Hilkoil will cover the cost of what the insurance company refused to when your house burns down or floods after the steam explosion, GREAT! ;-)

    Seriously, to later sell your house in MA you'd probably have to yank the thing out (as well as your hacked-up woodstove) first.

    To do wood-fired hydronic systems legally in MA you need to use an outdoor wood boiler, that appears on the approved list. I'm not sure if Lunenburg has any further restrictions (probably not), but many higher-density towns restrict wood burning appliances for local outdoor air quality reasons.

    But this is beyond the scope of the initial question. Bottom line, yes you can give a modest boost to the hydronic systems embedding a PEX loop in the hearth to utilize the wood-stove heat in it's thermal mass, but it's probably not worth the effort.
    Last edited: Feb 29, 2012
  9. Hackney plumbing

    Hackney plumbing Homeowner

    Messages:
    1,174
    Location:
    Alabama
    So is the Hilkoil approved in Maine or not? I'm about to call Hilkoil and ask. I'd hate for you to run them through the mud because you dont like Hilkoil. Its either approved or not........no probably.

    Ok I called Hilkoil. The guy was really nice and said the tubes are tested by UL and to check with ALL local code departments before installation. He said they are schedule 40 stainless pipe. You can add as many safety devices as you want.
    Last edited: Feb 29, 2012
  10. Supervisor

    Supervisor Construction Supervisor

    Messages:
    7
    Location:
    Lunenburg ma
    Hey Guys,

    Thanks for the input, I am simply thinking to use some of the heat that gets driven into the concrete/brick mass that is my hearth, and circulate water through it and back to the manifold that is connected to my slab in the basement, It did not seem to me as if it would be something that would be "against code", as I am not actually interfacing the two combustion systems, but simply using the hearth as an air to water heat exchanger, I was thinking using copper instead of Pex because of the unknown(to me) at this point of the actual temp that the hearth will get to, But I will be checking that link you sent Hack, I would like to understand more....especially the controls side which seems to have no end.

    Thanks again, Chris
  11. Hackney plumbing

    Hackney plumbing Homeowner

    Messages:
    1,174
    Location:
    Alabama
    Thanks for posting. I understand your not looking for the coil I posted a link to but thought it could be a consideration of yours if you had not seen it. I was thinking of going solar for water heating and some space heating but during long periods of no sun I could fire an outside stove off with one of those Hilkoil tubes in it to make hot water.

    It seems the hearth floor wouldn't get hot enough if you put the pipes in the floor because the heat would mostly be rising.
  12. Supervisor

    Supervisor Construction Supervisor

    Messages:
    7
    Location:
    Lunenburg ma
    Thanks for the input Hackney, Dana, I think that Hilkoil coil is rather interesting, I think if set up properly could be very useful, but also a coil inside the firebox has a potential to create steam.

    I am going to send something through the hearth to attempt to capture some heat, I may set it up with a temp sensor on the supply and return to see what I can get out of it.

    I spoke with my balancer (air/water) and he stated I should get the primary hydronic system up and running for at least a year before I start "screwing with supplemental stuff" as I might be opening Pandora's box if there are any issues with the new boiler/radiant/controls etc, even reputable qualified contractors run into situations where they have issue's with getting a system to function in the manor that is expected, adding this wild card could complicate the troubleshooting process and actually cost extra.

    Thanks again guys, I will let you know how the temp reading go.

    Chris
  13. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,319
    Location:
    New England
    MA is VERY particular about anything plumbing, and first, if caught, you'll get in trouble if you do any plumbing if you don't have a license, even in your own home. So, doesn't really matter what approvals things may have on a national basis, local control trumps that. Things that don't have a national approval are unlikely to make the MA approved list, but it is definately not certain to be approved for use in MA, even with a national approval. Not sure if they separate HVAC/hydonic from potable and waste plumbing...you'd have to check.
  14. Dana

    Dana In the trades

    Messages:
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    Location:
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    The heat in the hearth is already inside of conditioned space, so the only thing you're achieving with the coil is the ability to move that heat to another room/zone. I'm not sure it's worth the trouble- the heat tranfer rate between the woodstove and the hearth is only about 2 BTU/hour per square foot per degree of temperature difference.

    Say the bottom of the woodstove is 4 square feet, the surface of the hearth directly beneath the stove is a pretty-warm 120F, and the wood stove is a way-too-hot-to-touch 300F. That's a delta-T of 180F, times 4 feet = 720 BTU/hr. If the hearth is warmer than that, the transfer rate drops, if the wood stove is hotter than that you have to put on an asbestos suit to get near it. Considering your whole house heat load at a modest 30F outdoors is probably 15,000BTU/hr, how much of a boost is 720BT/hr? A 300F wood stove in 70F room is already pouring more than 5,000 BTU/hour into just that room. (Say it's ~4 square feet per side, 6 sides, the side facing the warm hearth is putting out 720BTU/hr, but the other 5x4 =20 square feet times a delta-T of 230F for 4600BTU/hr, giving a total of ~5320 BTU/hr, enough to heat a substantial sized room/zone. Ideally what you'd want is to be able to pump away a larger fraction of it's total output to remote zones, but with primarily just the bottom of the stove facing the hearth it's just not in the cards.

    The Hilkoil folks claim "Exceeds ASME, ASTM and US boiler codes", but they don't have any of those certifications. They also claim, "You're covered by product liability insurance", but offer no details. I couldn't find any test report listings other evidence of ETLM testing & labeling in online searches either (where did you find that?), so I'm not sure what that means relative to legal installation in Maine, but it's doubtful.

    Even if the components might meet some sort of spec, the manner in which you hack up the stove is unlikely to meet any sort of safety agency spec, and any user-modified system would likely absolve the manufacturer of liability. At the end of their installation instructions is the disclaimer:

    "We make no warranty covering consequential damages, incidental
    damages, or incidental expenses, including injury to persons or
    property, which may occur during the use of this product.
    "

    I'll believe that part, eh? ;-)

    If the fuel source for your radiant is oil or propane, you might want to consider putting the "supplemental stuff" money into a mini-split air source heat pump, the output of which costs about half that of oil or propane at current Nat'l Grid electricity pricing (a bit more than natural gas heating, but not a LOT more), and it'll air-condition at high efficiency too. It's not a cushy as warm floors, but you can raise the temp to make up for it on comfort-factor and still save big on the heating bills. Even if it's only covering half your space heating energy it's a measurable dent. (During the spring/fall shoulder seasons it's more efficient than geothermal, and CHEAPER than natural gas at current MA gas pricing, and more likely to cover the entire heat load then.)
  15. Hackney plumbing

    Hackney plumbing Homeowner

    Messages:
    1,174
    Location:
    Alabama
  16. Dana

    Dana In the trades

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    Location:
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    [​IMG]

    Couldn't find an online access to the ETLM listing for 80-08-109 to know what level of UL testing was performed to know what it really covers.
  17. Hackney plumbing

    Hackney plumbing Homeowner

    Messages:
    1,174
    Location:
    Alabama
    So what did they do...listed it and give it the stamp but then in the fine print say it cant be used? LOL

    Until you can find somthing that says it cant be used.......I'd drop it.

    I cant prove everything.......lol
  18. ballvalve

    ballvalve General Engineering Contractor

    Messages:
    3,261
    Location:
    northfork, california
    Before anyone buys a hilcoil - PM me, I have govt surplus SS rigs with about 3 or 4 loops, looks like submarine quality. Also a pile of palleted heat exchangers, also gov surplus, about 4x4 feet with a beautiful 120v long and quiet fan included. Top quality brass and copper coils. had so many, scrapped a few - but they are new. Think I got 450$ for one rig. We - our govt. paid over 12,000$ for each. I'll try and post a pic soon of these - really useful for utilizing wood heat with water.

    A great system would be a section of stovepipe wrapped with that sewer water flat copper pipe that Dana has posted for shower drains.

    I'll carve a potato "UL" stamp and mark my rigs for you. Like the chinese do.
  19. Hackney plumbing

    Hackney plumbing Homeowner

    Messages:
    1,174
    Location:
    Alabama
    I would love to see some pics of those exchangers when you get a chance. Very cool.
  20. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,319
    Location:
    New England
    As I said earlier, MA is very particular about what gets used and approved in their state... http://license.reg.state.ma.us/pubLic/pl_products/pb_pre_form.asp

    If it's not on their approved list, you'll have troubles. Not to say you can't try to get it approved, but if not already done, it can be a pain. Hilcoil gets no hits for approved products.
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