can you do geothermal and radiant floor heat?

mrb123October 15, 2004

I am confused. We are looking for a cost efficient and comfortable way to heat the house that is also as clean and dust free as possible. Which is the best option? Do you do both? What is the source of the heat for the radiant floor heat and does it work to cool the house or must you do a forced air A/C unit anyway? Most important, which is the most economical at installation?? Please help!!!! Thanks!!

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I'll tell you that radiant heat is by far less prone to be dusty / dirty etc. It's comfort is unbelieveable. You will want water at about 120 deg F or so; geothermal can easily generate that. Geothermal is just a way of generating heat . . . . it is not necessarily connected to radiant type heat; but it does lend itself to it very well. I happened to use a conventional 50 gallon water heater for heating my entire house here in central New York state.

As with most things; up front costs can be high with geothermal; though energy costs are quite low. How well the system holds up will likely be a big determinant of the overall cash picture.

You CANNOT do cooling with radiant type "heat" . . . it will do a poor job of dehumidifying the air; and any cooling that does take place will tend to condense moisture at the coolest point . .. that would be the floor. Not a good scenario to set up.

" Most important, which is the most economical at installation?? " Don't think this should be the major factor at all. A cheap forced air furnace would likely be the cheapest to install, or electric baseboard. While cost is a factor to all; will you be uncomfortable with results of the cheapest system; and derive comfort from the fact that it was cheap ? I think not. Many times spending more up front will give long term benefits in more ways than financial.

I did my own radiant heat install; it was NOT the cheapest way to go. But, it indeed is quite efficient and without question exceptionally comfortable and clean.

I can answer further specific questions about radiant heat if you're interested . .. . .


    Bookmark   October 15, 2004 at 6:43PM
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thanks Bob..I guess I was wondering which was going to be more economical between the 2 systems. I have heard geo-thermal(on this site) may be only as much as a $3000-3500 more investment than standard HVAC. If radiant heat is much more and then I have to add on the cost of a/c and duct work I am wondering if i am not better off with a duct system that is purely geothermal for both heating and a/c but cleaner b/c it is a truly closed system that does not involve a furnace exchanger that will draw in dust from the house and expel it back out EVERYWHERE, which is what we had in our new house 3 years ago and HATED. Any thoughts? I am not against radiant in floor at all but am wondering if I want to get into a seperate a/c situation. Thanks.

    Bookmark   October 15, 2004 at 9:00PM
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Forced air blows whatever is in the house; around. Period. If you have to have A/C; don't know any way around ducts etc. Geothermal is cheap to run; initial installation is more but that depends upon what type. It also depends upon having a good, properly done design by someone who knows what they're doing.

There are some places out there that charge absolutely outrageous amounts for radiant heat and installation . . . it can be had quite economically . . . and if DIY installation of it is within your abilities ( time more than anything ); it's tough to beat in the overall picture.

If you're doing new construction; don't forget an ERV or HRV; in a tight house you HAVE to have it. A tight house will tend to be "cleaner" as the only outside air coming in will be THROUGH the ERV / HRV which are filtered. In an older, less tight house you are sucking air in through all kinds of little leaks all over the place . . . this may well be a source of much of the dust etc. Also consider that any type of carpeting is going to contribute at least some amount of fibers etc. Again; radiant and hardwood floors are inherently very dust free.

Don't know enough about geothermal to say if it's capable of generating hot enough liquid to do forced air via a heat exchanger . . . we are all accustomed to forced air being quite hot. A warm mass of moving air can feel cool; especially in winter when humidity levels tend to drop. You need hotter air for it to "feel" warm if it's moving. No such issues with radiant heat.

Don't know if I've answered your questions or not . . . if not ask again . . ..


    Bookmark   October 17, 2004 at 7:47AM
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I asked my contractor the same question yesterday and was told that his "systems engineering guy" recommended against combining the too as this may lead to the system being out of balance. Does this make sense? Most of our first floor will be hardwood. I have spoken with flooring reps who proclaim their wood floors are designed to be used with radiant heating. Anyone with experience with radiant heat under wood floors (and a geothermal heat system as well)?



    Bookmark   November 3, 2004 at 4:29PM
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Radiant in-floor heat and hardwood floors play JUST fine together. I've got nothing but hardwoods; maple and white oak. Been here 5 years now with nothing BUT radiant heat. I used real hardwood flooring installed completely normally EXCEPT installed directly upon the subfloor . . . no paper or such of any kind.

Geothermal is simply a way of obtaining heat other than by burning fuel or an electric heating element. Radiant heat doesn't care where it's hot water comes from . . . it could be a wood burning stove, a conventional water heater by propane, NG, or electric or solar or whatever . . or a geothermal heat pump. If the g-heat pump can supply sufficient hot water to provide your heating needs; then it is indeed ideal for radiant. I have no idea what "out of balance" means other than the guy hasn't done one / isn't very familiar with them.

Radiant heat is incredibly simple technology; though some "versions" put in all sorts of doo-dads to make it seem more impressive. Geothermal is very basic principles as well; in a PROPERLY designed system the cost of operating can be very low. Installation is usually quite steep compared to other systems . . . . step over that dollar to save a dime . . .

Anyway; I see nothing BUT inherent compatibility between radiant heat and a properly designed / installed geothermal system . . . . find someone who KNOWS the stuff to work out your design . . .


    Bookmark   November 3, 2004 at 6:35PM
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We just moved to CNY and are planning to build a home in the spring. Wondering if you have any recommendations on contracters, builders or retailers in the area who can consult with us on geothermal, wind power (we're not too far from the always windy Tug Hill Plateau) and other forms of renewable energy.

We're your basic untalented, unmechanical, not-too-bright homeowners who have to hire everything out, so the option of DIY just ain't there.

Are you off the grid?

Thank you.


    Bookmark   November 8, 2004 at 1:15PM
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I was in a shop once where they had run cpvc pipes in sand and then, over that, poured concrete over rebar for a concrete pad. I don't really remember how they heated the water, but they pumped it through the pipes and they really, really liked it. Is this what you folks are referring to when you speak of radiant heat? If so, it doesn't sound like that should be so expensive. Still, I suppose everything does "add up" doesn't it? I plan on building a new, small house and I think this is something I want to try. Encourage me, please.

    Bookmark   November 12, 2004 at 9:53PM
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Yes, that is essentially radiant in-floor heat. The Romans used it . . . they didn't have PVC pipe or boilers or such; but they ran heated water through channels under the floor. So, it is by NO means "new" . . . uncommon perhaps or unknown; but not new.

Sand, concrete etc all offer a "thermal mass" . . . which helps to make a place feel comfortable. It can also be done underneath a conventional wood framed floor as well with the use of plates and such to hold the tubing up, and to help it spread it's heat evenly over the floor. Which method is best depends upon your actual construction and layout. The tubing can be layed directly IN the concrete; PEX is a very commonly used material and has a good, known, long history of successful use for radiant heating. If you do a slab on the ground; you'll want to insulate the slab FROM the ground; lest you be trying to heat the planet. Also know that this type of heat is inherently NOT good at doing quick temperature changes such as a forced air system can do. Set the temp where you want it; and leave it there. Toss out that programmable t'stat as well . . . .

It never ceases to amaze me; the amount of money you can pay for such systems if you want to. But; I believe you are inherently correct in that it need not be expensive. You can add all kinds of frills to it; but nothing beats a well-done design, properly installed; for a great combination of comfortable / efficient heat; and long term trouble-free system.

I did 1800 sq ft about 5 years ago for $2200 matl's; water heater and installation not included in that as I did it myself. Not tough to do; does chew up some time but nothing complicated. Email me if you have more specific questions . .. I'll try to answer them for you . . .


    Bookmark   November 13, 2004 at 7:41AM
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Yes, now that I think of it I saw the Roman system on a History channel program or somewhere like it.
The shop I was in was an auto shop and they were always opening the doors, so I thought the system was out of place, but they wouldn't be without it even though they had a big gas furnace, too.
If you put the pipe or PEX in the concrete are there expansion-contraction concerns?

    Bookmark   November 14, 2004 at 1:16AM
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I know that copper in concrete DOESN'T work . . . PEX is done all the time. It is even done in outdoor situations to melt snow from sidewalks etc. It must be tied up properly with the rebar, and must be pressurized at the time of the pour to keep it from collapsing. Beyond that; I can't give you much detail as I did not do mine in concrete; I have staple-up.

The people in the business certainly can; they've got the experience / knowledge; and it's obviously in their best interest that it works right and well and is reliable. I'll suggest Radiantec; I did my system through them and they were a great bunch of people to deal with. There are others out there too to touch base with . . . no matter who you go with; there should be a concensus of how to do it properly in concrete.


Here is a link that might be useful: Radiantec . . . .

    Bookmark   November 14, 2004 at 6:00AM
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Thank You, Bob!

    Bookmark   November 14, 2004 at 11:41AM
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Geo works great for hydronic pipe in cement but is problematic when put with hydronic pipe in wood. Wood embeded systems realy need a little higher temperature than heat pumps can efficiently manage to do satisfactorily in colder weather.

    Bookmark   November 24, 2004 at 6:17PM
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Bob ,

I am DIYing my own Geothermal / radiant system and I had a couple of questions for you . You mentioned a water heater - did you use a geothermal
heat pump in addition or instead of ? I am using a McQuay water to water
pump . I have a fairly large home so I have a lot of costs in materials but I
didn't see your excavation costs . Mine is going to work out to roughly
20k in materials - Pex , manifolds , loops and pump . The excavation will
be 1500.00 for the trenches . I have done a great deal of research but I
am a little worried about installing the ground loops . That would be very
costly fix if I mess it up ! LOL How difficult was your installation ? Any info
you can give me about your experience would be helpful . Thanks Faye

    Bookmark   September 9, 2008 at 1:21AM
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In my new home we have a 5 ton geothermal heat pump and 6 zone radiant heat system. The geothermal also dumps over into a hot water tank to supplement our instant hot water so that it only has to heat from 110degrees to 130 (no small children in our house).

I will say that we have some kind of new system...only the second one in the state of NC to get it. The company rep had to come out for the install...and it looks like it belongs on Star Trek.

Our builder quoted us $15k for the traditional forced hot air. We paid approximately $41k for the ground loop (Not vertical) install of the geothermal. We got 6 zones to alleviate the marital stress caused by the thermostat wars.

We pay an additional $200 per month for the cost of the geothermal on our mortgage, but expect to save about $250 in utilities. That will be a net savings of $50 per month.

We moved in this past August, so I won't be able to say how wonderful the radiant floor heat is until sometime late November, early December here in North Carolina.

I will say, even with the red clay surrounding me the dust hasn't been that bad with the forced air A/C. We got an energy star rating of 54 to give you an idea of how well our envelope is sealed. BTW the Air is run thru the geothermal heat pump, so it is running our AC, and cooling very well. No extra heat pump at all.


    Bookmark   September 14, 2008 at 12:34AM
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You mentioned water getting condensed on the floor if radiant floor cooling was used.
Can this situation be avoided by taking care that the cooling is above the dew point of air and complementing the system by installing small, cheap, easily replaceable but effective hygroscopic substances?

    Bookmark   October 15, 2008 at 2:11PM
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egrigby, I am also in NC and considering geothermal and radiant heating. Would you mind sharing who the installer was for your system?

    Bookmark   October 18, 2008 at 9:54PM
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Sorry Percip, I didn't get back until just now. We used Bowmen Mechanical. He is Raleigh area based. Hope that helps.


    Bookmark   November 26, 2008 at 3:30PM
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I sent a separate message or comment on your web page. I was wondering how the winter is going in NC with your Geothermal/radiant heat system. I live in SC now but probably moving to PA closer to where I grew up and considering building a new home with geothermal / warmboard system as well as A/C and desuperheater. Winter we'll use a tankless water heater backup. Any comments about the comfort level in the winter would be great. I'm also thinking of Tulikivi radiant fireplaces in several locations in the house.

Dave Cline

    Bookmark   January 11, 2009 at 7:14AM
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I have a basement and first floor with radiant heat. Since it is a closed loop system with approximately 17,000 linear feet of PEX, would there be any value or sense to using Geothermal?
The Geothermal salesman pushed and pushed, but could not explain to me why I would need to create 55 degree water when the water in my radiant system will never get that low.

    Bookmark   January 26, 2012 at 9:48PM
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Alex House

How are you heating the water with your present system? I'm going to assume that you're taking city water and heating it in a boiler and then circulating the water or using a heat exchanger to transfer the created heat to the water.

When you turn on your tap water and release cold water, that water is usually not a tepid 55 degrees, it's colder, which means that your system has to input heat from, say 40 degrees, up to what is needed. Geothermal brings two advantages, 1.) the water is sent into the ground and picks up heat, bringing it up to 55 degrees, or whatever the temp is in your locale (the sun heats all the earth around you and you're extracting a little bit of this solar energy from a cubic footprint of ground) and 2.) the heat pump compressor creates additional heat more efficiently than heating direct by electricity and natural gas.

In a nutshell, here are the two stark alternatives:

1.) Let's assume that this is your system. Take city water at 40 degrees, burn natural gas to heat it to 120 degrees, meaning you have to burn natural gas to create BTUs which are then transferred directly to the water.

2.) A geothermal system with a loop field, starts at, say 55 and then the Heat Pump uses electricity and refrigeration principles, to heat the water up to 120 degrees but does so 3-5x more efficiently than a direct electric heater would.

You're getting free heat from the ground (55-40) and the 15 degree differential (or whatever it actually is) is exploited by the heat pump which uses the embodied heat within that water to boost its temperature even higher and then sends the cold water that the process produces back into the ground where it soaks up the solar energy that has been "planted" into the ground and the process starts all over again.

    Bookmark   January 27, 2012 at 6:36PM
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