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geothermal hot air

Posted by astace (My Page) on
Wed, Oct 29, 08 at 18:16

I'm looking into a geothermal conversion of my house which has forced hot water. I'm worried it will be too dry with the forced hot air. My old house had hot air and we hated it. Humidifiers never worked. We'd love to have radiant floors but would have to tear up 4600sf of floors to convert. Do people find the geothermal hot air system too dry? Is it worth doing even without the radiant floor system? Thanks

Follow-Up Postings:

RE: geothermal hot air

It's the combustion and venting of a gas-fired warm air furnace that tends to dry the air because the exhaust air vented out is replaced with dry cold air that infiltrates or is brought in purposely to replace the vented combustion products.

Being that a geothermal unit, typically has no gas-fired stages, this would not occur. If your gas boiler is not sealed combustion, then in fact the geo thermal by theory would be better, yet air-movement and the process of enhanced skin evaporation may be confused as dry but the indoor RH would be about the same.

With regards to adding a humidifier, perhaps you had a drum unit that required maintenance, but today a good humidifier would work well for you with no issues as long as simple maint is performed.

I can't answer the radiant easily, however I'm sure it's close in cost to a geo unit or more with ductwork installed. Radiant can be installed on top of flooring if willing and able to give up about 1" or from below if accessable.

RE: geothermal hot air

I have Geothermal heat and needed to add humidifiers to them because the house was too dry in the winter even without combustion as Z points out. I installed Honeywell humidifiers which have drip filters - not the drum kind - and they really work well.

I purchased 2 Honeywell 225B units, each which came with a auto control humidistat and also allows for an external thermometer to be connected - which you definately want. The humidistat/controller will use the outside air temp, inside air temp, and inside humidity level to control the humidity level. I saw the humidity increase from about 33% to 44% in about 2 days after we installed them.

I would also recommend the purchase of a few standalone tstat/hydrometers which cost about $20 to $25. Put them around the house so you can monitor what the humidity is in various rooms.

Honeywell makes a 225A and 225B unit - the B unit has the Auto Contoller but only costs a few dollars more than the A unit. The outdoor thermomter is an accessory and costs about $29. Check out for pricing and more details.

Best of luck.

RE: geothermal hot air

Hello ~ I just had geothermal installed in my home this fall. I used to have radiators and while I did love them, I felt I needed to switch. So far, we have had a mild fall/winter, but I have not noticed the house being too dry. I know that geothermal air comes out of the ducts at a lower rate (i.e. it doesn't blow as hard) and also a lower temperature. In other words, you don't get very hot air blowing out of it like traditional systems. So, I thought this was why I haven't noticed it being dry. Obviously others have noticed this though... just thought I'd add my 2 cents worth.

Also, thanks for giving me the idea of recording humidity. I have been recording the geothermal energy use as well as outdoor temperature data, I will now add both indoor and outdoor humidity.

Good Luck!

RE: geothermal hot air

I figured geothermal would have quite a bit higher register temps than a conventional heat pump would. I know my heat pump register temp is great at 50 degrees out and very mediocre at I figured using the 50+ degree earth to pull heat out of would be similar to a 50 degree outside temp with a heat pump.

RE: geothermal hot air

The output tempertaure at my registers is about 85 degrees with the GT heat pump running properly and No Auxiliary Heat. I measured this last winter during very cold outside temps (~20 deg) at a time when we were having some start up issues with the GT system. I am not sure how that output temp compares with gas,oil, or conventional heat pumps.

The humidity issue has a lot to do with outside air temperatures and the capacity of air to hold moisture. Cold air has less capacity to hold moisture then warm air, so when the temperatures drop outside the humidity will tend to drop (unless you have a rain or snow storm blowing in ). A combustion furnance which will have a much higher output air temperature will only compound the humidity problem by further drying the air. Since GT heat pumps have lower output air temps, they dry the air less than a gas or oil furnace will.

I recommend getting humidifier units with geothermal systems if you live in a cold region. Make sure you follow the instructions carefully since the ducts for hunidifier have to be installed differently than you would for gas/oil heat.

I would also check the basement humidity levels frequently to see if you need a de-humidifier as well. I found that in hot/humid summer, as well as in winter when there was precipitation, the moisture levels in the basement were very high (above 70%) and I started to get moisture spots on the concrete floors. In time this would have led to mould issues.

I have quickly come to realize that I need an IAQ system to manage the humidifiers, de-humidifier, and a future ERV that I will be installing. I am looking at the Honeywell Vision Pro IAQ contoller that can manage all of these components from a single programmable contoller. Currently I am doing a lot of manual checking and adjusting which was initially OK while learning, but now that I understand what is happening and why I am ready to automate it all.

RE: geothermal hot air

We bought a 2 year old foreclosed house with geothermal heating. The man that built the house was an engineer an dreally put a lot of elite mechanics in the house--including geothermal and a honeywell humidity system
My husband and I are pretty much clueless to this system. We live in Indiana, which is about 13 degrees right now. Our lowest level (basement) usually would be the warmest in the entire house. It would be at 74 degrees while the rest of the house was @67 degrees. (We have a two story with a basement)
Lately, the basement just has been hanging out at 59 degrees. Does this have anything to do with adjusting or needing to adjust the humidity control? We have never really even known what to do with the humidity controler.
Can you tell us how to set in the winter and summer?
Thanks, Jodi

RE: geothermal hot air

Hi Jodi,

The temperature drop probably has nothing to do with the humidity system. Your system should have an electric plenum backup heater, is there a call for backup or Aux heat on your thermostat? Is there a circuit breaker in your electrical panel for auxiliary backup heater; is it On? It may be the largest (capacity) breaker in the panel, probably 60-amps at least.

Has the previous owner left any info as to what comprises the geothermal system, i.e., type of ground loop, how may feet, installation start-up data, loop temperature/pressure data. Do you know who did the installation? Perhaps they kept and have a record of all the installation data. What make & model heat pump do you have? Is the house zoned, how many square feet is it? Thats quite a temperature differential between floors! The more info you can provide, the better guidance were able to offer.


RE: geothermal hot air

Re the quote by sniffdog: The output temperature at my registers is about 85 degrees with the GT heat pump running properly...

Our system was installed 3 years ago. That first season, I made baseline temperature readings for both heating and cooling modes, using the register nearest the unit. Heat output was 97 degrees, cooling 55. However, this winter we seem to have an issue. the best I see is about 89 degrees. If the unit runs for an extended period, the temp may fall to 86. I realize that the output will fall off a bit when it's very cold outside (it's been in the teens), but losing 10 degrees of output temp seems excessive, at least to me.

Anyone have a thought on whether this is normal?

RE: geothermal hot air

Yikes. Could a moderator, if there is one, please delete my email address from the previous post? Thanks.

RE: geothermal hot air

If you have HWBB now I would look into geo hot water so you don't have to go through the expense of running ductwork. If your floors are warm enough now I would say they will still be warm enough even if you change your boiler for a heat pump. We just put in electric mat under kitchen tile to see how it works before we put it in the master bath. We never use it - the toekick vent my geo installer put under the sink warms the floor there enough we don't need to turn on the radiant heat. We will put in in the bath though since vents are in ceilings upstairs.

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