when will geothermal work with hot water radiators?

Discussion in 'General Discussions' started by Bill, Jun 30, 2011.

  1. Bill

    Bill New Member

    I am interested in switching to geothermal for my heating and AC, but live in an old house (built 1928) with a natural gas/hot water radiators system. Geothermal will require installing duct work for the forced air heating. We have some ducts, since we installed central AC, but not enough for heating.

    I am told that geothermal cannot produce enough heat for hot water radiators, but that the technology is improving. Does anybody have any sense of when it will be able to work with a heating system such as ours? I know this is difficult to predict, and nobody out there has a crystal ball, but is this something that seems to be a year or two away, or is it over the horizon? My current systems work fine for now so I could wait.
  2. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    It does

    Climatemaster/carrier has a 150f unit for this purpose. Waterfurnace has one coming out as well.
  3. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    Cop not very good a that high, better to augment th radiation.
  4. docjenser

    docjenser Well-Known Member Industry Professional Forum Leader

    High temperature units with plate exchanger are available. It depends on what kind of radiators you have, and what your heatload is.
    While COP is not great at 145 F load temperature, the unit comes with an outdoor reset, lowering your load temperature when it is not extremely cold out side. At the 32 EWT AND 104 LOAD TEMP the unit has a COP of 4.2, which is extremely high compared to the 3.0 energy star minimum.
    What kind of radiators do you have, and where do you live? Climate?
    Last edited: Jul 2, 2011
  5. Bill

    Bill New Member

    I live just outside of Washington, DC. The average low temperatures in Dec – Feb are 29, 24 and 27. The mean temperature for those months is 39, 34, 37.

    Most of the house has old-fashioned cast iron radiators. The kitchen, which is in an addition, has a separate zone with baseboard radiators.
  6. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    If you have old cast Iron radiators, you may find you have enough extra capacity for lower water temps.
  7. Designer_Mike

    Designer_Mike Member

    Side question from an "observer".
    Could he replace the radiators to improve the heat transfer (if the piping is large enough)

    Also are their any radiators with small circulator fans built in to move some air?

    I have a friend in a similar situation that would like to go Geo
  8. Mark Custis

    Mark Custis Not soon. Industry Professional Forum Leader


    Yes to both of your questions.

    I think Joe's first response to this thread is the best idea. The Dead Men all used boilers and usually sized stuff to handle 180* or higher water temperatures, so sending geo warmed water to said radiators may not provide enough BTUH on a design day.

    If the home has been upgraded with insulation windows and sealing the envelope it could work as Joe mentions later.

    There are now low temperature radiators in the market. One would need to look at how the system is piped and add radiation carefully so what is existing will work with the additional stuff to be installed.
  9. zacmobile

    zacmobile Guest

    low temp rads

    as stated above outdoor reset is key, you may only need the maximum system temperature for a week out of the year, the rest you will very likely be well below that (depending on tightenss & insulation of your house & square footage of installed radiation). i have a condensing gas boiler with panel radiators in my place and I think the rads have only hit 120F a couple of times that I can remember, most of the winter they are 90-95F or so. My dad has original old cast iron rads in his place that were running off of an old R-22 ClimateMaster GSW and likewise I don't think they ever went above 120F. Mind you when design outdoor conditions hit the system could only do a couple of hairs below room temperature. He has since upgraded to the ClimateMaster THW for that extra oomph during cold spells (100% geo DHW too!)

    You would do well to do a room-by-room heatloss calculation & figure out how much square footage of radiator surface area is in each room too, that way you can get a good idea of what kind of temperatures you really need. There is some good info on figuring out radiator square footage over at HeatingHelp.com, also the Burnham heating helper handbook has some tables for this as well, if you e-mail them i'm sure they would send you a free copy.

    Also, a good manufacturer of low temperature rads is Jaga North America
    Last edited by a moderator: Jul 4, 2011
  10. Designer_Mike

    Designer_Mike Member

    I will assume any attempts to use the radiator system for cooling would result in lots of condensation issues.

    Are there any cooling options for a hot water radiator system conversion without the expense of adding a lot of ductwork?
  11. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    Are there any cooling options for a hot water radiator system conversion without the expense of adding a lot of ductwork?

    Controls to monitor humidity and allow radiant cooling until the dew point is met.
  12. Designer_Mike

    Designer_Mike Member

    More detailed please?..
    Are you are saying that you monitor the dewpoint and then restrict the radiator fluid to stay above that temp (thus no condensation)?

    I'm sure your cooling potential is somewhat limited BUT it sure beats the cost of adding a bunch of ductwork and in a primary heating climate, like New England, cooling requirement is probably minimal anyway (otherwise you would probably have AC ductwork)
  13. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader


    It is more an on/off feature. Cool until condensation would be an issue.

    In my climate that would mean slab cooling diverted to fan coils by a humidity control.

    It is very climate dependent (it is arid here). If you are predominantly humid you may have minimum useful run times for radiant slab/radiator cooling. I'm lazy enough tonight to not look up your specifics. But that is the idea presented as an option to your original question.
  14. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    One could look at hydronic consoles if the floor plan is relatively open. Much like installing mini splits you can cool without a duct system.
  15. zacmobile

    zacmobile Guest

    radiant cooling

    as stated by urthbuoy keep fluid temps below dewpoint and all will be well, going further though you can keep the humidity down by adding some ventilation like an HRV or ERV and for even more dehumidification you could add a chilled water coil in the return air from the space. this would be about 1/4 of the ductwork of a fully ducted geo forced air system.

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