Thermal mass

I'm also debating adding a steel plate that spans the top of the stove across the blocks that would stop heat from instantly rising and hopefully force it outwards

 

Even some pavers on top to close them off will help against the convection.

In the end this (closing the top) is not a storage change but a rate of heat release change. I.e.do you want a little per hour for longer or a bit more (still relatively little...) fora bit shorter.

Adding water would increase the storage.

 

Just flipping the top row on their sides would block the rest of the stack off...

 

Yes, I had thought that at first, but given that he says the top ones get hottest, that likely is due in part to higher radiative load (and heat from the bottom ones rising up).
Putting the top ones sideways allows that radiation to "escape" through the holes.

I'm not sure how much all this in practice will affect things, but it's the principle that counts

 

You could fill those blocks pea gravel and top them off with solid blocks. That’s what I did with my sauna stove.

 

I’ve been trying to figure a way to use water for thermal mass besides setting a pot of water on top. I like the idea of using PVC. In my sauna I’ve measured the block temps as high as 350 so not sure if that’s too hot?

I’ve also looked into cast iron radiators but they are very pricey, even old used ones. My 5 gal pot of water on top of my stove is still warm 24 hours later after a good fire. Water can really hold the heat for a long time!

 

It's gonna boil and make steam...either be gone, or if captured make high pressure.

 

The wife is not thrilled about how this looks.
She made sure it wasn't (permanent)
She wants her house to look nice when we're not heating.
So even though I like the pea gravel idea if better not do that.
I'm hopefull she decide this is a battle not worth having once spring comes around.

 

The way it is now it could be removed for the summer pretty quickly/easily...you could also get end cap blocks for a cleaner look too...and/or use concrete stain to "paint" them, that would spruce things up if done correctly

 

Yessir, removing 35 cinder blocks ain't no biggie, if I added pea gravel or solids or water things would start to get irritating.

 

Any red bricks available? They'd fit in the cinder block spaces quite nicely.

 

Right, but I don’t know how hot the insides would be. Anyways I was thinking about the water thing for the OP. If I did it in my sauna it would freeze when I’m not using it.

 

Of course it all depends on the temperature inside the blocks. One would have to add a safety margin too; in case of a runaway fire you don't want to end up with also melted pvc and water everywhere (at least, if the fire is still contained in the stove )

The water should not boil. For humidity reasons, but also because it really doesn't contribute to the goal then: energy storage.
But it's easy to get there; move the water farther away or have it cool a bit faster. The energy "load" going into the water decreases quadratically with distance. So, you could set filled pipes on the outside of the blocks if you need them farther away. The goal is to get them to 180 F or so (a fairly safe margin below 212). I would always add a 1/8" hole in the top; some steam or boiling is preferable over a hot explosion. And its sputtering/bubbling serves as a warning that hings are getting too hot.

 

Keep us posted on how this works out. Did you try burning the stove after you removed the side shields before adding the cinder blocks? That alone may have given you what you were looking for? You also have the mass of your home and everything inside that the stove can heat up instead of a more convective stove that mostly heats the air.

 

No sir did not burn it with no side shields before I put block up.
Was worried about melting the couch

 

Yes. That would be counterproductive to the whole thermo mass experiment!

 

Water is 8+ pounds per gallon. Most home floors have a weight limit of 40 pounds per square foot. (40 pounds includes people and their stuff)

Bare minimum your extra support also needs (more) blocking to help stop the beams from twisting.

 

What R value is in your walls? Add any exterior insulation? Does your basement have any insulation? What about windows single or dual pane?