Installing geo thermal in an old house with boiler?

September 28, 2009 8:07 PM

Installing geo thermal in an old house with boiler?

I am considering buying an old (1910s) house with a boiler and radiators installed. I was thinking it would be great to convert it to run off of geothermal. How difficult/expensive would this be? I live in Kansas, so we need good heating as well as cooling for summer. I was hoping to accomplish both with a geothermal system.

posted by idyllhands to technology (8 comments total)

According to this Canuck site it's likely to need a fair bit of work, as well as additional radiators (assuming you have the old iron ones and not the newer rads with fins.) Most of the geothermal retrofits I've heard of have involved installing new and larger ducting (source: the neighbour at our old place does this for a living and told us about a few he's done, including his own 1915 two-storey.)
posted by Hardcore Poser at 8:58 PM on September 28

You're talking about a heat pump with a geothermal loop, correct? I priced it awhile back out of curiosity and it'll run you about $10-15k for the heat pump and ductwork, plus $15-25k for the geothermal loops, depending on how they're installed.
posted by electroboy at 9:57 PM on September 28

I doubt if you'll get any cooling from an ordinary geothermal system in the summer. Unless you use an drilled hole and a system where you can reverse the heat exchange (ie loading the hole with heat during the summer). Even that wouldn't be very efficient, I believe.

Regarding the radiators: Here in Sweden our installer was delighted that we had the old, clumsy radiator-type since its more suitable for the (reatively) low heated water that our heat-exchanger produced. Our house is from 1942, and is situated in the south of Sweden (about the same latitude as Riga, in Latvia).

As for how difficult it was: Not very. The installers yanked out the old boiler and put in a new shiny refridgerater-type of closet, made some new pipework and that was all for the inside-installation. Outside they drilled a muddy hole and later we had to fill up with dirt and sow grass.
posted by Rabarberofficer at 11:26 PM on September 28

I'm assuming you mean a ground source heat pump.

If saving money on energy bills is your goal, spend money on windows and insulation first. You'll get a much better ROI. Once your house is nice and tight, then start thinking about a GSHP system.

In order for a GSHP to work well, you need to think of the entire system. Ducts should be well-designed and allow for smooth air flow. This means smooth ducts, not accordioned flex-pipe. You want well-designed air flow otherwise you're wasting money. Or you could do hydronic floor boards, but that'll cost a lot more. I don't think you can do it with radiators, though I could be wrong. It won't work for cooling, in any event.

You can do cooling with a GSHP. All you do is reverse the flow during the summer. It's way more efficient than a regular air conditioner and central A/C is awesome.

You'll need plenty of space in your electrical panel. When the heat pump starts up (which it'll do a couple times an hour in the winter) it uses a lot of current. You also might have back-up resistance heaters in the ducts which will use a lot of current if you need them. I have mine shut off, since we use the fire place as backup.

Shop for a company that has been doing GSHP for a long time. These systems are all the rage now so HVAC companies are sending guys out for 1/2 day training classes and then selling systems. These guys aren't going to do it right and you'll have a poorly-designed system that'll cost too much to run.

Additionally, the ground loop, either open or closed, will need to be sized properly. Like the HVAC companies, a lot of well drillers are jumping on the GSHP bandwagon and selling people undersized ground loops and not grouting them (in the case of closed loops) properly. They do this because the cost of a properly sized ground loop often scares people away.

If you already have a water well you might be able to do it all on the cheap. If you need to do a closed loop, a horizontal or slinky will be cheaper but you need to have the land for it. A vertical closed loop is the most expensive.

It can be done, but expect a retrofit to cost a lot. Again, with an old house you should first focus on tightening it up.

There are a lot of green energy and geothermal / GSHP enthusiasts out there posting on green energy forums. You should search them out and ask around.
posted by bondcliff at 6:42 AM on September 29 [2 favorites has favorites]

yeah, using the old cast iron radiators actually requires higher temp's (not lower temps) in order to create a circulation of air against the wall (the rad should be about 1-2in. forget the formula - from the wall) the old cast iron rad's are great, but getting water (assuming not steam rad's) to ~180 deg takes more than most "green" systems can do...

The geothermal takes advantage of a particular range of heat/cool differences (not talking technically here (check out wikipedia for a better overview)... so you'll need an exchanger of some sort - a heat pump.

Forced air is generally your only option for this.

If you wanted to go heated water for winter - using an "add on" system with an extra hot water tank to store heat and run across a water-to-water exchanger - these guys have the beginnings of a nice solution on the market: Radiantec.

But that's off topic a bit... the geothermal stuff is cool, deep well geothermal is great if you're not near areas where you have to worry about what's below your property.

If you really really wanted to keep using your radiators and use the GT or other systems to simply raise the heat level of the water, then use something else to "do the rest"... I've done an odd hybrid system for a part radiant floor, part cast iron radiator heating system that used an electric booster unit (the ones sold for restaurant/commercial diswashing) piggbacked onto a water-to-water exchanger that took heat from another system and raised the overall temp to the required 180 deg for the rad's... so it is *possible* though there's always loss in transitions between fluids in systems - just as there are losses between the Geothermal water running through the water-to-air exchanger in the blower/air handlers....

dunno if any of that was helpful?
posted by Jiff_and_theChoosyMuthers at 9:23 AM on September 29

Another benefit of the heat pump/geothermal setup is you can use a desuperheater to use the waste heat from air conditioning to heat your hot water.
posted by electroboy at 9:55 AM on September 29

The house doesn't have duct work, which is why I thought I would use the existing radiators if possible.
It comes on a large lot (half acre), so I think I could bury a lot of piping.
posted by idyllhands at 6:23 PM on September 29

well... I think you'll need to read up on what Geothermal can and can't do...

the ground simply cannot heat water to the temp required for where radiators work best.

GT works on the differential (just like the crappy heat pumps that electrical co's like to have installed in further and further north areas)... using the the ground/ground water as the vector to something like a water/water heat exchanger (better surface area, better transfer of heat - in quick/loose terms) where the air heat pumps that use the delta in outside air temp for their heat sink (air is a much worse performer in heat transmission)... both these systems rely on an exchanger inside the house though... they use a blower behind an exchanger/evaporator (same function, named evaporator for what's going on inside the tubes... but still a form of heat exchanger)... where fins/tubes are getting heated/cooled.

See How Stuff Works.

And here's a company in the DC Metro area that has a little quick info on how the system compares to other (also AIR HANDLER/DUCTWORK systems - doesn't compare to radiant, as GT doesn't work in those heat ranges):
GT Options
posted by Jiff_and_theChoosyMuthers at 9:31 AM on September 30