Geothermal radiant heat

[nemise]

Has anyone done this that can weigh in on exactly how it's done and if it's worth it? Doing a garage addition and I plan on doing radiant heat inside the slab as well as on the 2nd floor. Looking for the most economical way of heating the spaces. How would geothermal work, and is it worth it over getting a high efficiency tankless water heater to heat the water?

 

[anthony666]

i've done tons of those jobs .. a general rule of thumb in HVAC, the more efficient and the lower the cost of operation, the bigger the buy in

geo is typically at the pinnacle of buy in cost .. unless you have a lake/large pond or artesian well real close to your house, or you own a back hoe the ground source cost is gonna kill ya

 

[kd3pc]

how big is your garage...the cost of the system may dwarf the entire build of the garage. Where are you? Anything cold is going to render the tankless, useless.

IN my experience, there is NOT a tankless water heater that can raise the delta in the residential system, enough to heat it. You will just be burning $20 bills to maybe warm the water. Concrete is one doozy of a heat sink.

It is only worth it, if you think so.

 

[nemise]

Garage is 26x32 with living space about, so about 1700 sq ft. I want to size it to do the existing house too, about another 2000 sq ft. I am in new england (MA).

I called someone to get a price of a geo system, and I think when I see it I'm probably going to end up sticking with a high efficiency natural gas furnace/water heater rather than going geo.

I currently have an Eternal tankless water heater for my hot water needs and in the summer when I use gas for the stove/oven/grill/dryer/water my bill is only like 15-20 bucks a month. I'm thinking if I add this system on and stick with a HE heater I should be fine.

 

[anthony666]

Eternal tankless water heater for my hot water needs and in the summer when I use gas for the stove/oven/grill/dryer/water my bill is only like 15-20 bucks a month. I'm thinking if I add this system on and stick with a HE heater I should be fine.

i cannot stress this enough .. make sure the manufacturer ok's that unit for space heating .. a regular tankless water heater is not the right animal for the job

 

[nemise]

Correct - I plan on purchasing a separate unit for heating. They said not to use this one for radiant heating.

Any recommendations on what I should use? Water heater or boiler? Brands?

 

[theoldwizard1]

i've done tons of those jobs .. a general rule of thumb in HVAC, the more efficient and the lower the cost of operation, the bigger the buy in

geo is typically at the pinnacle of buy in cost .. unless you have a lake/large pond or artesian well real close to your house, or you own a back hoe the ground source cost is gonna kill ya

Correct !

If you have natural gas available, it is very hard to beat the installation and operation cost.

The exception is areas of the country that have large annual cooling loads. I can not believe that there are not more geothermal units installed in places like FL, TX, AZ, NM and SoCal.

 

[anthony666]

Correct - I plan on purchasing a separate unit for heating. They said not to use this one for radiant heating.

Any recommendations on what I should use? Water heater or boiler? Brands?

yes i do .. navian ncb series .. it's a combi, which means it has a circuit for heating and also an independent circuit for domestic hot water .. you can ditch the eternal, sell it on craigs or something, and put this one unit in it's place

trust me, you won't regret it

 

[yeldogt]

In my area (rock) the costs for drilling the wells make the geo very expensive. Even with the tax credits and propane back-up air heat pumps still win the price war. It becomes even more out of each with NG.

anthony666. How does the Navian work with colder well water for DHW? I bought a winter vacation house about 7 years ago with a tankless and we did not like it .... I understand some of the newest variable output ones are supposed to work better with the colder winter water input. I put one in a bathroom addition for a summer place and it worked great in that application.

The long wait and the difficultly with doing a loop has me thinking of maybe a Veissmann with a small HW holding tank for my new build. #222-F

 

[anthony666]

anthony666. How does the Navian work with colder well water for DHW? I bought a winter vacation house about 7 years ago with a tankless and we did not like it .... I understand some of the newest variable output ones are supposed to work better with the colder winter water input. I put one in a bathroom addition for a summer place and it worked great in that application.

most of my jobs are rural and i haven't heard any complaint about the navs not heating well water properly .. what was the unit you had the bad experience with ?? could it have maybe been a problem with scale build up on the heat exchanger ??

ive done some jobs with a small holding tank and circ pump .. kinda defeats the purpose of having a tankless

 

[jives]

We have a Baxi Luna propane dual (domestic hot water and radiant floor heating) tankless
heater and it does both without a hiccup. 2200 sq ft house, 8 persons, tons of laundry
and showers and it supplies hot water from our well without problem. Now, if the cost
of propane would fall. . .

 

[yeldogt]

most of my jobs are rural and i haven't heard any complaint about the navs not heating well water properly .. what was the unit you had the bad experience with ?? could it have maybe been a problem with scale build up on the heat exchanger ??

ive done some jobs with a small holding tank and circ pump .. kinda defeats the purpose of having a tankless

That house had a Rinnai. In the winter the water (heat) was marginal and the summer it was too hot ... and it took too long for the hot water to get to the most distant bathroom.

They are the rational product.

 

[anthony666]

Rinnai

rinnais are usually great .. the tankless lag is usually the reason for the looped storage tank

kind of a stretch, but did the water pass through an unconditioned space ?? like through the attic or something .. that would **** the heat right out of it in winter, it might have gotten cranked to compensate and then in summer with no cold area to chill it ....... i guess it's academic now, you don't have the place anymore ??

 

[yeldogt]

I still have the house. The problem was that the water was just too cold coming out of the ground in the winter. It worked OK or better ... in the summer. The house really needed two units .. each closer to the areas needed .. impossible installation.

The previous owner installed it ........ my solution was to put back a 30 gallon oil fired unit that the on demand replaced. The house had two oil fired heaters .. and big oil tanks .. so it was an easy retrofit. It's a weekend house -- the oil unit heats the tank in 15 min ... and I installed one of the loop pumps.

I really want to use the on-demand units on my rebuild ... but a small tank unit may be better.

 

[anthony666]

thinking on the problem, it couldnt have been an unconditioned space, woulda probably burst the pipe if it was cold enough to drag the heat out of it

must have just been undersized for your location/requirements .. here's rinnai's online water heater calc http://calc.rinnai.us/ .. plug in your location info and maybe see if that model comes up in the results

 

[Jackfre]

Anthony is correct on this. The touch pad on the Rinnai can read not only the flow through the unit but the output temperature. It is very accurate. Read that and then the temp at the faucet. Generally the output temp drops about .4gpm per 10* temp reduction. Putting a tankless out in the north 40 is ridiculous. What model Rinnai is it? Get some temp/flow info and report back. The number one mistake on tankless heater installs nationwide is inadequate gas line sizing. There may be some of that going on as well. DO NOT use a Rinnai tankless for radiant. It is a great water heater. It is not a boiler. They have combi boilers for that.

 

[yeldogt]

We had two issues going on. One was the long distance to the bathrooms, the other was that it was an "on" or "off" unit ..... it had to be sized for the colder incoming well water in the winter. It was a big unit ... so it liked the hot water faucet open all the way otherwise the flow was not enough. It would cycle too much at any flow in the summer ... the winter was better.

While I like the idea of them ... the wait for hot water and the sizing of them has me worried.

The smaller holding tank of the Viessmann -- coupled to a hot return sounds like a reasonable compromise. I would only activate the return when we are using the house. I turn the oil unit off when we leave.

 

[Jackfre]

Find out the model number. The earliest units had a minimum flow of .6 gpm and 15kbtu to initiate flow. Later models, about 2004 on, had .4 gpm and 10,000 btu and hold operation down to about .25 gpm. Distance and pipe size are the culprits frequently. The real answer is to move the water heater closer to the point(s) of use. That saves water, reduces energy consumption and minimizes wait. Keep in mind that the cross sectional area of 1/2, 3/4, and 1" pipe is .19, .44 and .77 inches and you can see how to large a pipe exacerbates the problem.

 

[Jackfre]

As well, my apologies to the OP. This post went sideways for him. We should take this to a separate post.