Existing Homes, Rocket Mass and Heat Flywheels

ONE of the HUGE problems I face is, my unfinished basement doesn't lend itself well to the  common rocket mass heater.  However, always a fan of the "if there is no solution, there cannot be a problem" approach (within reason, of course). Mindful of that, here I go:

(1) My house sits on a first story of cement blocks. Those blocks are totally uninsulated on the outside.  

(2) I rented a house on the coast of the Pacific Northwet. It, too, had one story of concrete blocks exposed to the weather. Like my current daylight basement, there was no insulation outside.

(3) I enclosed that Pacific Northwet rental's basement by installing a double pane picture window (1/4" tinted glass from a skyscraper project purchase mistake) and a door (to the elation of the landlords).  After that, I installed wood heater. The basement was, otherwise, unheated.

It would take about three days for the wood stove to heat the concrete blocks AND the concrete floor. When they come up to temp, they would hold the heat for a couple days. The heat was a nice, comfortable heat.  In other words, the basement was like a heat flywheel.

(4) Had I or the landlord insulated the outside of the concrete blocks, the efficiency of the heat flywheel, a/k/a basement floor and walls, would have improved even more.

(5) Were I to insulate the exterior of my current concrete block walls (upper third on the east wall and all of the west and south walls, those walls, along with the concrete slab floor in my house, could be made into a worthwhile heat flywheel (I could add 2x6 framing for the insulation, and flashing would protect it well, from water penetration via the top, under the deck).

(6) Once all that was done, instead of the standard rocket mass approach, I MIGHT be able to press the piping against the concrete blocks, use a heat conductive packing to help transfer heat to the blocks, ALL while limiting the amount of mass the actual stove gets.

Essentially, instead of, for discussions sake, a long, 24" x 24" mass, I would build a mass just a bit deeper and taller than the pipe and try to move as much heat into the block.

It might even be the mass could be built outside and, again, up against the cement blocks, then WELL insulated to move the heat into the blocks.  

With the proper approach, the tunnel could still be feed from inside.

(7) In the end, one of these approaches or a variation of them may be an ideal solution to the problem of establishing safe, emergency heat.

( From the emergency point of view, there is also the matter of storing water. The large, 250 gallon and up toes would be ideal for this, but they have to be protected from freezing weather.

A small room, with a removable wall, to allow installation and removal or swaps of the water totes could tap that heat source. In our situation, the tote could be hidden under the deck to maintain the aesthetics of the property.

Any ideas on improvements, yea's, nay's. . . .?

There are a lot of different styles of RMH so it seems that one might work for you.

To me, the way most folks solve the insulation problem is by adding insulation to the interior.

For insulating outside, maybe some hay bales put next to the exterior would offer some help.

Insulation is a science, so to speak, of its own.  Until recent decades, no one insulated between concrete slabs and the ground they are poured on. Now, in recognition of that the contact with ground creates major heat transfers, many do.

If on the Washington coast, where electric cost is off the charts, the investment into insulation under slabs can pay for itself quickly.  On the east side of the mountains, where I can run my house and my 1,800 square foot, temperature controlled shop for $120.00/month or less, one might be less inclined to think about insulation, but will the cost of electric always be cheap?

Next, there is that it has become very common to insulate the outside of poured concrete and concrete block walls for the improved efficiency of heating and cooling.

Finally, take note of hotels, motels and many other commercial buildings being built. You'll see every one being built with not just interior wall insulation, but a layer of [closed cell] foam insulation over the exterior sheathing.

In my situation, bales of hay would be impractical. Properly installed, they'd be no less expensive than just adding 2x6's, insulation and sheathing.  

The bales would be under the second story deck on all but the north side, where the only choice is the interior insulation we are all familiar with (with allowances made for ridding the insulation of moisture).  This would mean sealing the top against moisture penetration would be more complicated than simple flashing needed for stick construction. Especially because the bales are so much wider than the 5-1/2" 2x's.  And there is that the bales would reduce the area under the deck used for yard equipment and ladder storage would be reduced to a walk area with some wall storage.

Anyway, yes. That was the reason for the post - using rocket mass heat, but not in the usual way (i.e., using existing mass by insulating it on the outside of the house) with only a minimum of added mass needed to pull off the project.

Anne Miller wrote:There are a lot of different styles of RMH so it seems that one might work for you.

To me, the way most folks solve the insulation problem is by adding insulation to the interior.

For insulating outside, maybe some hay bales put next to the exterior would offer some help.

The insulation on concrete slabs is just plastic so maybe wrapping your foundation with plastic would work.

Actually, they use rigid, closed cell foam under slabs. Because of the thickness of the concrete, area of slabs, and that footings around or through the slab carry the weight of structures, the foam is not totally crushed. It isn't a super high R value, but it reduces heat transfer through direct contact slabs normally have.  

That aside, plastic could have its uses too.  It could be treated like the moisture barrier on insulation. Depending on climate, the barrier would go on the inside or outside. Here, as you indicated, it would be inside.

The plastic would go a ways toward sealing against air movement, so would improve insulation quality and soundproofing, since sound is just movement of air.

Anne Miller wrote:The insulation on concrete slabs is just plastic so maybe wrapping your foundation with plastic would work.

That insulation is foamed plastic of one sort or another. Plastic sheets would be no more than a vapor barrier.

Running the hot exhaust channel (whether duct or linear bell structure) tight to the existing concrete wall would put a lot of heat into mass; as long as the wall was heavily insulated on the outside near the channel, it could work. The channel would have to be isolated from the floor, though, as except in newer high-quality construction that is highly unlikely to be insulated from the ground and would suck heat away from the interior forever.

Glen, I sealed up the daylight basement of a house I rented. It's walls were concrete block and floor was a slab. I installed a wood burner which, when used, took about three days to move heat into the slab and uninsulated walls to a point you would notice a difference with the stove not btu-ing.  When the stove was first started, the room would become very comfortable quickly, IF you still had your shoes on. After the three days, walking barefoot was comfortable.

No doubt a LOT of heat that didn't go up the chimney got lost to the uninsulated floor and walls, but it did take a couple days before you felt like you needed to fire up the stove.

So even less efficient construction can benefit greatly from the flywheel effect. I even notice the flywheel effect in our poorly built stick built upper area, above the concrete slab and block basement.  It takes a bit of time for the HVAC to heat the mass of the wood construction walls, vinal covered floors, furniture and such.  If you pay attention, you'll notice the difference after a few days of moving heat around into the fibers of the couches, chairs, the poorly insulated walls and so on.

Glenn Herbert wrote:That insulation is foamed plastic of one sort or another. Plastic sheets would be no more than a vapor barrier.

Running the hot exhaust channel (whether duct or linear bell structure) tight to the existing concrete wall would put a lot of heat into mass; as long as the wall was heavily insulated on the outside near the channel, it could work. The channel would have to be isolated from the floor, though, as except in newer high-quality construction that is highly unlikely to be insulated from the ground and would suck heat away from the interior forever.

You can't do much about an uninsulated slab, and it will eventually get comfortable if you keep heating the space; but heating the slab directly under the duct is just loss with no benefit of comfort underfoot. I would rather put the heat out into the general space and accept that some of it will be lost to the earth later, than send it directly to the earth.

Our slab acts like a thermal mass because it helps heat our house in the winter.

Our only heat is a propane heater in the living area though the slab keep our unheated laundry room at 60 degrees all winter. It also keep the bedroom warm because it is unheated except for an electric heater at night.

Of course I am in sunny Texas though it gets down to minus 7 degrees for a day or two.

I did what was suggested to some degree. I insulated the ground with 2 inch Styrofoam in sort of a box. then added 400 tons of crushed rock to act as a heat sink to my concrete slab. I then poured a slab with the concrete having pex tubing running through it. Using a program logic controller and a boiler, I heated the concrete.

It sort of worked.

There is no free lunch because physics does not change. Energy can neither be created nor destroyed, only moved or converted.

It kind of worked because once the concrete and rock mass was injected with heat, it radiated it off. Radiant floor heating works different because it heats the OBJECTS in the room and not the air. It is like having a four-hundred-ton radiator under your house. If the power went out, and the boiler went down, I only lost 1 degree inside for every day the power was off. And even unheated for a winter season, the coldest it ever got inside was 40 degrees on a -7 below zero (f) day. The ground had enough heat to keep the house above freezing. But it was not warm enough for comfortable human occupation.

But it did not work in some ways because that big radiator has to be heated. In the fall it was hell. The boiler would run when it was cold at night, then shut off during the day when it was warm out. Then the cycle would start again at night, the slab and rock adding heat and releasing it in an endless, useless, expensive way. The only way to combat it was to wait until it was cold both day and night, making for some cold living situations. Then I would turn on the heat and in about three days of hard core operation, heat would start getting into the slab so we could start to feel it.

Incidentally, I had the same thing putting rock behind a pot bellied stove. It really was not worth doing because controlling the fire was easier than trying to use massive rock behind the stove to take out the highs and lows of an intense fire.