hydronic heating 'versus' RMH || +thoughts on hydronic heating/cooling versus geothermal earth tubes

Years before I finally actually got moved out of the city and to this little piece of land where I now live, I dreamed of a rocket mass heater... about a year ago I finally got things established enough to move into a very small house and almost froze the first winter, so it's time to get back to thinking about heat (at least for NEXT winter, as for this one looks like I'll be hauling more propane). I would love a masonry type RMH with a vertical feed like these https://www.dragonheaters.com/content/dragonheatercastleweblit.pdf, as I could use 1-2" diameter branches of which I have SO MANY that fall to the ground of the forest,,

yet, then the other day I started down the exciting rabbithole of hydronic heating and cooling. and got to thinking... as elegant as such heaters (above) can be, couldn't it maybe be even neater to just pump and heat some water I already want to use in barrels in the greenhouse for keeping plants alive over winter, and run it through a heat exchanger / radiator fan type deal? (loving these videos:  https://www.youtube.com/user/desertsun02  )

It seems like even without crunching astronomical amounts of data it's probably safe to say the electricity needed to run such a heating system would be CONSIDERABLY lower than electric or propane heating, but would it be low enough to compete with the efficiency and permaculture of a RMH? what about the more obvious pros/cons like having/not-having to deal with masonry, bulk, weight of a RMH...?  --for example, even if RMH is much more efficient (which I'm not sure if it's more or MUCH more efficient than hydronic heating), perhaps the cost and effort (and having to reinforce my house's foundation with additional footers under the masonry heater I would want as opposed to a barrel thingy)...might make hydronic heating the clear choice in my case.

In the back of my head for some years I've also had this plan of maybe some day trying earth tubes for heating/cooling air, and then recently found out about what I guess is more common: liquid / heat exchanger/ heat pump type geothermal systems... and while i'm not opposed to almost killing myself digging trenches in the forest (if you haven't trenched in the middle of the woods, pretty sure you haven't really lived :P), the thought of simply pumping and heating water with solar thermal means of some kind and then heating my house's air with that... seems potentially like a big AHA! moment  (especially when you consider such massive earth-moving exercises are a BIG what-if you might have to dig up again no matter how well you plan it out, it seems to me).

So far I've only done something like level 2 (of 10) research on this so far, so a little more than scratched the surface, but now hitting lots of forking info and possible paths!

I'm more interested in solving for heating, but I am also super curious how an electric chiller for hydronic cooling might compare // if there's ANY hope of that being worthwhile compared to electric AC (plus good old heat acclimation, which I do try to utilize as much as possible). Again, cooling seems more iffy/tricky. without an additional chiller, cooling a 400 sf house on 105 degree days with just earth cooled air/liquid might be a challenge, or maybe not. I mean even 80 or 90 is better than 105. But I don't want to do massive earth moving just for cooling (if I can accomplish heating without digging at all), and I'm not sure if a chiller+fan would be any more efficient than a conventional window AC.

would love to hear others' experiences / thoughts!!

I have NO EXPERIENCE with earth cooling, but I have with Geothermal Heating and Radiant Floor Heat.

In my chicken coop, at one time I dug a 100 foot trench, 4 feet underground where here in Maine it is 57 degrees all the time. Using a fan, I blew air from one end that started in the coop, out through the tubing to the other end that was in the coop as well. No matter what the temperature was outside, it increased the temp in the chicken coop by 20 degrees. For MOST days, this meant the coop was above freezing, but not always. For instance, if it got down to 10 degrees outside, it was 30, or below freezing in the coop. So the number of days of having frozen water in the coop was much, much better, but it was not perfect. The coop size was 8x12, 8 feet high, and insulated. It had no other heat...

As for radiant floor heat, I have pex running through my home which is 2200 sq ft of heated space (total my home is 2600 sq ft). Last year it was vacant because we moved to a Tiny House. Because of the inherent geothermal heat, my home never went below 44 degrees. This is cold, but it was a VACANT HOUSE, and the temp outside was -7 degrees (f) below zero. That is pretty cold. At the time I drained my heating system, but now realized I never had too because the house never got below freezing.

Before I drained the floor I just ran the "heating" system which was the water flowing through the floor, but with no boiler warming the water. In this way the water in the center of the floor was 57 degrees, but of course on a radiant floor home, you only lose heat in the outer 3-4 feet of the home, not so much in the center. By running the floor's pumps, that 57 degree water is lowered as it circulates through the outside parts of the floor, but my home never gets below 63 degrees as long as the floor is circulating. Again that is pretty good.

My cost to run my circulators in my heating system (3 of them) makes my electric bill go up by $10 in the winter.

It makes little sense for me to try and get hydronic cooling in the summer because it would only warm my floors since the vast majority of my square footage is already at 57 degrees. It does get warm in my home, but only about 4 PM to 8 PM when the heat in the attic eventually settles down enough to make my home uncomfortable. I live in Maine so it does not get hot here often, but if it did, attic vent fans would be cheaper, and work better than trying to use geothermal cooling; but that is just me, and where I live.

Most heating advice begins with: "Plug the leaks" and "insulate". Then cover the windows at night when it's cold out so you don't lose by radiation. And wear a sweater and get good blankets. IOW, conserving warmth pays back faster and cheaper than any heating options.

Choices: Make a list of what each option requires and what it offers. Ie. RMH requires the proper prepared wood and a certain amount of space and structure in the building. Forced air heat usually requires a gas energy source, a small light furnace and some way to push the hot air where you want it - w/or w/out ducting. Hydronic requires a boiler with a heat source (wood, oil, gas), piping to carry heated fluid to the radiators you decide on; radiators can be the traditional type, tubing in the floor or ceiling or walls, maybe a heat exchanger in a duct if you want blown hot air. IOW, hydronic requires plumbing. Fireplaces of various types require space, structural support and more or less line of sight to areas they need to heat; in theory you could also plumb in hydronic heating into a fire place but now we're talking rocket science and monopoly money. Passive solar heat requires glass and mass and like the fire place, direct line of sight to the area you want heat in; also sufficient sunlight. Electric baseboard heat requires baseboards and wiring and a grid hook up. This is usually the cheapest to install and maintain and one of the more expensive to fuel (electricity, at the moment, is more expensive than gas or, in the right place, wood). But, it's very small light foot print in the house, heats instantly and regulation  room by room is trivial allowing very fine control w/in the house. Geo hydronic requires a heat sink/source reachable by excavation, plumbing, and sophisticated heat transfer system, pumps, etc. The ground loops need to be carefully engineered. It's another version of hydronic, on steroids.

The above is no way inclusive, of course. Make a spread sheet of requirements, features, pluses, minuses, costs, availability, politically correct or not... Add rows and columns as you remember stuff you're interested in.

Other thoughts: Consider KISS - Keep It Simple Stupid. That's always a good idea. Cheaper, more reliable, more people will understand and not screw it up, more repairable.  Who will you trust and believe in to build your system? Who will repair your heating system for you? Somebody less than a day and a $thousand away, hopefully. What heating system fits the character of the house and of the neighborhood?

Regards,
Rufus

Hey there Travis,

Thanks for sharing your real world experience! That geothermal chicken coop setup is pretty much exactly the simplest heating method I'd really wanted to be able to do just that --project my models into real space/time and see if it's as functional and efficient as imagined. My house is almost 4 times as big as your chicken coop, so conceivably I could do 4runs of 100 ft. I realize temp differentials are going to be different for me/I would need to do my own adjustments, but this is very heartening!

And that radiant floor heating sounds ideal --your experience gives me a real solid idea of what kind of benefits and return I might expect if I were to install radiant heat flooring. 44 degrees when it's -7 is pretty darn impressive!!

Hiya Rufus, thanks so much for your insights. Yes, I keep learning this more and more myself-- "Plug the leaks and insulate". Each time I ride out a very cold night I learn more how true this advice is. I mean when it's 70 degrees outside you just don't think about the windows or this or that tiny hole, but when it's 20 degrees and no amount of blankets are doing the trick, suddenly things like a simple thick blanket to cover windows... jump out at oneself. And though I've lived here full time a year now, I'm STILL learning things you just don't when you are encapsulated in a constant climate controlled environment, like "just put on more clothes!". Too true!

And thanks for your breakdown of some pro/con requirements of the various heating types. Exactly- electric is expensive, definitely trying to avoid having to use that, unless it's just to run a fan portion of heating perhaps.

My house is 384 SF (ceiling avg 10ft) and has sprayed foam insulation (1/2 depth on walls and ceiling, just enough to seal drafts under the floor -maybe 2-3 inches), and utilizes typical post and beam construction.

Interestingly, I'm seeing a combined sort of inspiration from overlaying both your posts... radiant (water in tubing) heating but rather than in the floor (not keen on cutting holes in my joists or scraping underfloor insulation), I could run heated tubing in the walls, since I have the wall insulation only about 1/2 depth.

Running radiant heating in the walls would be much simpler in my situation (than floor). I'm also still thinking even less work would be required to heat the water and run it through heat exchanger to blower, but obviously it wouldn't be as efficient...

#1 (radiant heat in the lower walls) - would clearly be MUCH more efficient --as the medium doesn't need to be as heated and doesn't lose that heat as much as #2 (using that same medium to heat air and blow it into the house), but #2 would be much simpler to set up and I wouldn't have to cut holes in wall studs.

I suppose I could do a pretty simple experiment without getting in too deep: make a solar heated exchanger / blower thing and see how hot I can get that air in the wintertime. Because that seems like the missing piece for me now, to answer the question... "just how hot COULD I get that blowing air without supplemental boiler/ how much supplemental boiler might I need?"

So here's where I'm at:

1: plug and insulate: Before I go crazy trying to decide or even calculate more about heating methods, plug and insulate more. >> This house is up off the ground on piers (1.5-3ft), so just adding skirting around the bottom would help significantly. Finishing insulation inside, and making good insulating window covers for winter nights, will make a HUGE difference.

2: ...then the amount of required heating would be so reduced it may be such a game changer that the smallest most efficient heating method would be perfectly adequate. I could start by trying out the heated water to exchanger/blower.

..for now it looks like I'll winter with the existing electric oil radiator plus propane heater on coldest nights, then set about finishing insulation and heater experiments for next winter. I'm trying to lower cost of living all round, and still getting some basic infrastructure established, and it's just me doing all this, so I think in the hopes of maintaining sanity I need to keep heating as simple as possible, meaning even if it costs a bit more to run, going with an option that requires less setup work since I have no shortage of labor intensive tasks needing doing.

Loving how your contributions are fleshing out my models and helping me decide stuff! Thanks guys!!

Yes, you have to finish insulating. Since radiant floor heat does not heat the air, but rather heats the objects in the room, there really can be no drafts with that kind of system. But any drafts should be stopped on a home first.

There are ways you can install radiant floor heating tubes inexpensively, but as you said, by the time you get done plugging the holes, you may find the return on investment is just not worth having what is probably the best heating system out there with the current technology that we have (This Old House Magazine: November 2019 Issue). What I tell people to do is; picture their home filled with water and tuned upside down. Anywhere water leaks out...fill with insulation. My radiant floor heating system is state of the art, but my home is also super-insulated, so there are reasons I am getting pretty good numbers

As for my chicken coop, just keep in mind that was a chicken coop. I suppose a person could heat a home like that too, but in order to keep out the earthen smell that will inevitably come from driving air through the ground and back around again, a person would have to filter it. I am not sure how to do that, or what would work, I suppose a charcoal filter of some sort?

Cassie

You got it. Seal those leaks.

But here's a thought: Consider your existing house carefully and investigate in detail before taking any action. I don't know from your posts how much you know about design of habitat shells, nor what you may have already done. But you say that your house is insulated with sprayed foam and _that_ should make you think carefully _before_ spending time/money on more steps. Sprayed foam of any thickness is used to stop and plug leaks wholesale. It's one of the best uses of foam. Properly applied, 1/2" of sprayed foam should seal the whole wall, wherever that foam goes. You or somebody appears to have "taken steps" to seal your house. Additional insulation can then be installed over the foam to raise R-value. Thus, try to find out all the details of your shell, what was done and what is working. IF the foam is working as it should, that means that when you feel cold air blowing in, you need to look elsewhere for the source - or find that the foam was not installed properly and isn't working. Other leaks _may_ include:

- under the exterior walls where they sit on the floor
- up through the floor if there is no foam on the bottom of the subflow and joists
- around or through the window framing (not the windows themselves)
- "through" the windows, around the glass or sash holding the glass
- ditto for all exterior doors; weather stripping all the way round the door can stop all drafts there
- flues; hopefully the propane appliance has a flue so you don't die of CO poisoning and that flue is conducting your warm inside air up and out
- above the exterior walls where they meet the ceiling
- if there is an upper story with a stair door that you can use to isolate the upstairs, use it and seal it properly, just like an exterior door; I'm assuming here you can kiss off the upper level mostly until spring

Sealing is NOT the same as insulation. Sealing s/b done _first_ _before_ insulating (except in the case of blown foam which, when done properly, seals everywhere it's applied). Were me, I'd leave the skirting for last, especially if you decide to do anything under the house. MUCH nicer environment under there if it's not closed in. Skirting, depending on what you do, often remains mostly animal-permeable. It's nice and warm (relatively) under there and animals appreciate that... Insulate the floor from the crawl and make sure the craft paper or foil backing is stapled tight and true all over; this helps prevent wind washing the insulation that prevents it from working as planned.

I could go on, but really if you are planning on spending on this house, you should search "building science insulation", limit to the last 2 or 3 years and hunker down for some hours of reading, following links. Latest and greatest direct from the experts. Then concentrate on those approaches that look proper to you. People have been working _hard_ on these questions for the last 10-15 years but it's not all that difficult to understand and figure out what applies to your values.

One last quick/dirty ploy: Masking tape stops leaks, both air and water. Use the blue stuff or something even more expensive if you don't want to leave adhesive behind when comes time to remove it.


Cheers,
Rufus

Hi again Travis and Rufus!

Travis, yes, I get it: stop drafts :-) I don't think I'd mind the earthen smell actually, but I see what you mean.

Rufus,

But here's a thought: Consider your existing house carefully and investigate in detail before taking any action. I don't know from your posts how much you know about design of habitat shells, nor what you may have already done.

You said you can't tell my experience from my posts, so I'll flesh that out a bit... I think I said but certainly I didn't clarify I mean the house too, so: I'm doing all this on my own. I know everything there is to know about this shell . And I believe I understand the concepts of shells and insulation, since I was the one who chose and sprayed the insulation myself (so pretty sure I'm beyond the part where I need to spend more hours researching basics of heating and insulation), and would have thought it rather clear I have at least basic understanding of heating and insulation by the specifics of my original post. But thanks for playing it safe and assuming I might not know anything about heating or insulation whatsoever :P Here's a thought, if you're not sure about my experience, as you said, maybe ask instead of assuming someone else sprayed my foam and someone else decided it was best etc etc etc

I appreciate you making sure I go back to cover the basics, and as I mentioned, I agree those are worth considering yet again before sinking money into new heating system... and then beyond these basics, I was talking about wanting to compare RMHs and hydronic heating...

I appreciate what you say about skirting, and that was my thought (animals housing there) when neighbors told me how much more easily they heated their house once skirting went on... so maybe I'll just leave it open like I sort of wanted to to begin with, or make sure it is not animal-permeable.

Happy trails!

For cheap efficient heat, an rmh is hard to beat. Really, it is one of the most efficient heaters you can have and can be made for FREE, at least no money out of pocket but plenty of time. It does take a little skill to run it right, but any wood stove does.

Hydronic is really awesome, but there is a minimum level of complexity and cost that make it uncommon.  And most systems end up way more complicated than they needed to be.  I have seen complete off grid solar heating using a large water heat reserve, but nearly a quarter of the house cost went to the heating system.

I am thinking about it for my next house for the cooling, I have abundant spring water that is 60 degrees year round.  But that has condensation risks you have to be careful about or you turn your floor into a petri dish.

Cassie

The confusion I have is that a good spray foam insulation job should stop all leaks from the area where the foam is applied. But I had the impression that you find the house unpleasantly cold and that drafts are a real part of the problem. Drafts can be caused by cold surfaces like windows or by air leaks; in most buildings, we have both, but most buildings do not have spray foam insulation. That seemed peculiar. But then maybe it's the cold windows that cause all your drafts and you don't have any leaks. What I said was based on a best guess at your situation where it seemed the foam may not have stopped the leaks.

> RMH vs hydronic (broadly generalized)
They do different things. Have different footprints. Different costs. Impact the living space differently. Are operated differently. Use different fuels. Those things are already clear and understood, right? Which is a better fit for you?

It seems you have good willingness to speculate outside the box and dig in and address issues. Just beware the details. You know what they say about those...

Good luck,
Rufus

Hydronic Heat and Rocket Mass Heaters are actually very similar in a lot of ways; they both use intermittent firings to heat up mass that helps to heat your home. The problem with them, is that the heat is limited to wear the mass is located.

With a rocket mass heater, the cost is minimal because the mass is minimal. And the firings are made manually, and the performance based on the dimensions of the stove because there are very few controls...the burn defines the performance. And what can be used as a fuel is limited, not to mention a sizeable mass located inside the living area of a home.

With hydronic heat, the cost is more expensive because the firings are all automated, and the heat is distributed to the mass remotely. This requires the use of a boiler and controls. However these controls also allow a lot of options when it comes to fuel sources, and the size is incredibly small, my boiler for instance, is the size of a microwave and hangs on the wall.

In either case, neither is wrong, it just depends upon what the homeowner wants. If a homeowner is a homebody, and is home for most of the winter, then a rocket mass heater will work out fine, but if a homeowner travels a lot in the winter, then they may want automation so that their home can be heated when they are gone. That does not mean there are not work arounds; a person can get someone to babysit their rocket mass heater, or put electric heaters in each room they do not want to get below freezing, and go on vacation, but it is something that has to be done. With a hydronic heating system, it is automated, in fact it works bet when it is left alone.

If it seems I am negative towards a rocket mass heater, I assure you I am not, it is a low cost option, so a person is also going to get limited performance. With a radiant floor heating system, you pay for what you get as well. There are a lot of ways to heat with hydronic heat and save a lot of money, but there is also going to be less performance with those systems over ones they utilize more expensive controls. Again, you get what you pay for. Sometimes good enough is just that, good enough. Myself, I spent more up front, and reaped the savings over the long term instead.

If you plan to add other forms of heat like compost, firewood, co-generation, solar, etc, then hydronic heat would be a better option because you can just tap into the system and heat your home that way, but if those are things that do not appeal to you, then going with a single-source heating system may be better.

So, what's your floor plan like?
If you have an open floor plan, that lends itself to an RMH.
Heck,  you could do radiant heating with an un-insulated tank in the center of an open floor plan, but without much control.

Are all of your walls insulated/ sealed or only the exterior walls?
Either way, unless there is an aesthetic objection, a lot of work could be avoided by running radiant heat pipe on the surface of the walls.
An old school radiator or a spiral of PEX pipe could offer a lot of comfort.


I like digging, but I find myself avoiding plans that require  a lot of digging,, deep digging,  or any digging involving roots, rocks and other obstacles, so real geothermal is out the question for me.


I like solar, but the space is an issue in my urban yard.
In a place with more space, I could see building huge solar collector.
As things stand, any collector would have to be mounted on the walls of my home,  which is limited amount of square footage and already adsorbing solar, however poorly.
What is your land/yard like?


Maybe a rocket water boiler would serve you best.
A big un-pressurized, insulated vessel full of water heated by rocket stove exhaust.
Run a coil heat exchanger through this water to  preheat your DHW, tap off that same exchanger to  to feed your hydronic loop(s).
If you want to do solar thermal, add a coil for that.
Hydronic heating accepts all kinds of inputs.
One early retirement guru , Mr. Money Mustache, has a hydronic system that uses a conventional water heater.
If you have enough solar PV,  electrical resistance water heater would work as a source for a hydronics system.

If I had a pond, stream or such, I would use it as a heat sink, with a coil heat exchanger being cooled in it.
That I would tie into the forced air system, experience suggesting to  me that a even a room temperature  breeze cools me off better than standing kinda  near something very cold.