space heater question

[iFred]

Mind experiment.. Lets say that I have a standard 50,000 BTU space heater.

And sitting on top of this space heater is a solid block of rock 1x1x1 ft. I figure that once the block gets hot from the space heater that it would retain for a longer period the heat inside the block and be able to heat the room more efficiently for a longer period of time. So the question is, would doing something like this pay or not? And would I be increasing the efficiency and using less fuel as a result. Am I wrong or what am I missing? Thanks in advance.

[tecker]

   I would have to say that the block would do a good job of a kind of slow release of heat to an area .I started using concrete blocks to keep my green house from freezing

in early spring but abandoned the project because a compost pile worked better.I'm going to move the blocks close to my shop and give it another look .

[hiker]

come to think of it those compost piles do generate a lot of heat ,towards the

middle of the pile[been know to self ingnite]..

what about putting some copper tubbing in there--might be good for a small cabin..

can"t beat  that for heat[heat your cabin with garbage]..........

  the city here filled in an old city dump--built a small airport on top of the

old dump...a few years later you could allways smell this strange oder each time

you drove by..turned out to be methane gas!![one way to get airborn]..they had

to drill down into the old dump site and add a lot of vents and collecters..

not sure of what there using the gas for...thougth i might toss that in there....

[veewee77]

About efficiency and heating a rock. . .

While the idea seems like it would work, consider this. . .

It takes heat that would have gone to heating the room to heat the rock so during the hreating of the rock, you don't have as much available to heat the room.  Then when you turn off the heater, the rock dissipates heat into the room.  But over all, you have used the same amount of fuel to heat the rock and the room as it would have taken just to heat the room.  So it won't add any ( and probably less) efficency using the rock.

Unless. . .  You use solar to heat the rock then move it into the room. . .

DS

[nothing to lose]

If like other dumps I have seen, then they are probably just venting it to the air unburned!

 Yes compost piles produce lots of heat and methane, both can be used. I think the trick is building an encosure to catch the methane, building the pile so it has plenty of air and does not need turned, and not cooling it too low when extracting the heat or the process may slow alot.

With 12 acres of trees, it's on my list! I could use the compost anyway, and I hate the dry leaves laying around. I leave em lay now, but a fire hazzard when dry and they breed bugs, stop other growth etc... And I don't want to just burn them off.

I figure an electric or gasified tractor and blower to gather them for composting later.

[nothing to lose]

I think you neither gain nor lose anything except spreading out the heat over time, which may be a good thing itself.

Since it's all in the same room, it's all the same heat. Rock should be room temp to start and cool to room temp when done. If like me, a space heater provided to much heat too fast, then turned off the room got too cool to fast, then evening the heat out over a greater length of time would help alot perhaps.

When I used a kerosene space heater in an old trailer house for a weeks camping I had that problem. 5 minutes the room was too hot, 10 minutes after turning it off the room was too cold. SO rocks would have been a good thing for me. Actually I sat a couple old hot water tanks next to it full of water and that worked the same to spread out the heat. Plus  it had the advantage I could sit the space heater closer to the wall since the tanks protected the wall from excesive heat, so I actually got more living space too.

Bought it brand new for about $100 and used about 4 gal kerosene total probably, $2 a gal then! Haven't used it for about 6 years or more. Hmmm, I wonder if it would work on Veggie oil?? Thanks for reminding me about these things, gives me an idea, I'll dig it out of the shed, take it far into thte woods and see what happens!

I don't use it anyway so if it ruins it, nothing to lose

.

[skravlinge]

If you use fuel I don't think it is anything to win. Storing from say day to night may be good if it is solar, from  night to day if it is electric and there is night reduction on prices. If you use wood it is always good to store, the harder you push the heater  better will you use it, as tar or other stuff will be burnt and not  pass the chimney. It will be less not healthy stuff to the air. If you run the heater below its best working temperature it  seems to me, its better to push it up to the best level and store the heat for later use.

[Roamer195]

Any heater, electric or combustion based, will have a very high peak temperature if measured directly at the point of origin.

By the time this heat warms a room, it's dropped from something above 500 degrees F down to around 70 degrees F.

By placing a thermal mass directly on the heater, that mass will come up to a temperature somewhere between room temp and the heater's peak element temperature. It will reach it's own intermediate temperature and then will stabilize based on how well it can reradiate the heat into the room.

This has the effect of "smoothing" the rate of temperature change in the room, since the thermal mass will be reradiating at a fairly steady pace at a lower temperature.

[Gary D]

Hi Fred, oil filled space heaters are basicly the same thing you are thinking of. They heat oil, releasing it slowly into the air after the unit is off. But a watt is a watt.... or is it? How about a microwave heating oil, water etc. more work done with less watts? Gotta love brain teasers! Gary D

[picmacmillan]

hi fred.....pickster here........there is someone in barrie who put loads of rock under his house, first he put piping inside concrete foundation blocks(the 8" ones with the holes in it)... he runs heat through the pipes that heat his house and dryer , wood stove etc.., and the rocks stay warm he said for a long time...days or weeks i  forget.....pickster

[skravlinge]

The oil supplied electrical heaters, are most valuable if you load them on time when electric is cheaper and use the stored when its  not so. Electric heaters are as I know not  less  demanding of power than microwaves equipment, (unless you rather put the radiation on yourself  than heat the whole house). Dont try.

[Ex Mek]

 In some parts of Europe they pipe the Gass from garbage pits to gass turbines to generate electricity

  he block idea will work its just colecting the heat that otherwise would go into the room,and releasing it when the heater is turned off , same as a electric storage heater , sory there is no such thing as a free meal where energy is concerned

[skravlinge]

Right there is no free meal, but a meal can cost more or less.

[Gary D]

Without changing the heat mode, instead of a block on top of the heater would laying ceramic floor tiles in front work better? The radiant heat could fool the unit's thermostat (microclimate?) while the ceramic tiles would absorb a slight ammount of draft? Possibly allowing you to drop the thermostat a degree or two? Down side could be a cooler airflow on startup as the tiles absorb some heat if the heater has a fan making you want to turn up the thermostat... as you said braintease!

[finnsawyer]

So goodbye trees.  You seem to have the idea that your supply of trees is inexhaustible.  It's not.  As an example:  Where I live I figure an acre of woods produces 100 board feet of marketable lumber per year.  Double that for branches, etc.  A cord is 4 ft by 4 ft by 8 ft or about 1500 board feet if it was a stack of lumber.  De rate your cord by 50% because trees are not square.  So it takes 750 divided by 200 acres to produce a cord of wood in a year or about 4 acres.  So, when I was burning 5 cords of wood a year I was harvesting, in hardwood, the yearly growth from 20 acres of woods.  Since I had 40 acres at my disposal, it might look like I had it made.  I didn't.  Firstly, what about those trees that were producing good saw logs.  Can't touch them unless I sell the logs.  O. K. I started with a trash species called ironwood (Hop Hornbeam). Then poor grade trees.  Well, after a few years plus one small logging operation, the stand showed the effects of my attention.  Also, a good part of the 40 acres was in soft woods, which are not so desirable for heating, but might be alright for you.  I hope you get the picture.  Since you are planning to move in the near future, you're probably not too concerned about running out of trees now, but when you relocate you should make sure you buy enough land to support your operation.

Disclaimer: I make no claims about the accuracy of these numbers.  Check with your local forester.

[iFred]

Yes, it's a puzzler. But with all this info it suggests that it would level out the heat more evenly over time within a given space or as Roamer195 & nothing to lose;  stated; that it has the effect of "smoothing" the rate of temperature change in the room, since the thermal mass will be reradiating at a fairly steady pace at a lower temperature.

Which leads to the next statement with Gary saying, How about a microwave heating oil, water etc. more work done with less watts?

 Which I take it as "Latent Heat" - The energy absorbed or released during a change of state or the phases of equilibrium -  solid, liquid, gas. Would transitions create more work done with less watts over time span using different fluids, solids or gas's??

.

[TomW]

GeoM;

I tend to disagree with your opinion here. Not that I have any hard figures but I have been heating with wood my whole life. I happen to live in hardwood country so we burn a lot of oak, hickory, ash, etc.

We do have a substantial woodlot and with regular, necessary harvesting that keeps the timber healthy I find I can heat with wood on a completely renewable basis from logging waste [tops & culls] combined with deadfalls.

Even after an intense logging of the woodlot where I can see the huge holes in the canopy from harvesting the big guys after removal of a huge amount of biomass within 2 years the canopy has filled in and I believe the biomass is replenished in a couple years. I heat pretty much exclusively with tops or dead falls and seldom kill a tree for heat.

The other thing with a woodlot is it produces more cash from logging than the same area in crops. It also requires little or no input to do so.

Harvesting trees is quite important to a healthy timber if done properly. It opens up the canopy and allows sunlight to reach smaller trees and you remove trees that would eventually die and fall to the ground to rot. The bulk of the minerals and nutrients are in the leaves so hauling off the logs and firewood does not appreciably deplete the soil nutrients. We basically utilize about 50 acres of trees for heating simply because it is the easier part for me to get to than the rest of the farm. Just that 50 acre plot can produce $10,000 to $15,000 in logs in a harvest. Depending on weather, etc we can rotate harvest on that plot from 5 to 10 years. Not numbers from a theory but real world stuff.

Oh, we harvest a couple of deer per year from the timber, too which increases the value of the woodlot. We probably use about 5 cords a year altho I don't measure it just keep the wood shed full from year to year and it holds maybe 35 cords completely full.

I guess my point is that done properly on a suitably sized wood lot wood heat is completely sustainable and more. Just the view from here.

Cheers.

TomW

[iFred]

.

Heat is energy flowing from a high temperature object to a low temperature object. When the two objects are at the same temperature, there is no net flow of energy or heat.

Does this mean that once the room is at a certain temperature, that heating it further would be more or less a waste of energy since both the heat being radiated from the space heater and the heat of the room are at equilibrium?

This would then indicate that using such things as different materials in either solid, liquid or gas form during phases of equilibrium would help to increase the efficiency.

Another mind puzzle.. Thank you in advance for any comments!

.

[iFred]

I'm going to trow in some calcs here...

.

1. KW= 3,413 Btu/hr
   
1. KW = 1.3415 hp
   
1. Cubic Foot Natural Gas= 1,032 Btu's
   
   

c = specific heat for water = 1 Btu/lb/ F

c = specific heat for concrete = 0.2 Btu/lb/ F

Energy = Power x Time           Power = Energy/Time

Specific heat of air = 0.24 BTU/lb

Density of air = 0.075 lb/ft^3

Heat required to raise 1 ft^3 of air 1 degree F = 0.018 BTU/ft^3 *

degree F

[Gary D]

Hi Fred, Glad that you tossed this teaser out there. A phase change solid to liquid was put out by a poster to this board a few weeks ago... supposedly wax per kg. using a phase change could hold much more heat than water(did not research this myself). Don't know if wax expands much, but paraffin wax doesn't shrink during cooling (or wouldn't be good for sealing jam). Don't know if microwaving a sealed batch to the melting point would be safe tho...perhaps less total watts in than btu's out, similar to a heat pump ? The original thread was about solar heating storage I think. Gary D.

[finnsawyer]

Well basically, that's my point.  Scale your usage to what the forest can provide on a sustained basis.  It's a pretty subtle situation and the results of abuse may not show up for a generation.  Considering that the crown of a mature tree may cover a radius of thirty feet, when that tree is removed a sizable area stops producing wood.  The closing of the canopy helps, but regeneration is probably more important.  If the wood lot consists only of mature trees and one keeps removing them by successive loggings, in time the lot will be greatly impaired unless new trees are established.  Anyway, that's my view.

[TomW]

GeoM;

If the wood lot consists only of mature trees and one keeps removing them by successive loggings, in time the lot will be greatly impaired unless new trees are established.

I have seen this very situation on our other lot. It is from livestock grazing killing off the understory. Since we do not run livestock in the timber this problem does not apply to this lot I get firewood from. Anyway we use no real management other than keeping it free of livestock, cutting out the trash trees as i notice them while cutting wood and harvesting the mature trees and letting it grow the way it wants. Must be millions of small trees in there and as soon as they get some light in the smaller trees magically shoot up to great height in short order.

I am pretty well sold on wood being a viable, renewable biomass resource and also a source of cash on a rotating basis. Lots of people think of a woods as this open park like space under tall mature trees. A real woods is very nearly impassable from the thick understory. Thousands of trees per acre just waiting for a patch of sunlight to grow into. Harvesting a mature tree simply opens up a space for a few of them to really grow.  The difference is probably exponential. One big tree growing compared to dozens if not hundreds growing towards the spot cleared by the loss of a giant.

We have a fairly substantial area we let go completely other than harvesting occasionally because it had been heavily grazed and we are trying to let it rejuvenate. In 10 years of no cattle and no intense harvesting it has come a long ways back from being on the way to destruction. When I first started living here that area that was heavily grazed was like a huge park. Big trees and no brush and few smaller trees. After 10 years it is getting pretty thick in there and all we did was restrict the cattle and let it go the way it wanted. The way land is selling here I think all my effort will be wasted when we are gone and the farm gets chopped up for building lots "in the woods" and that will be the end of the line for a real woods.

Cheers.

TomW

[finnsawyer]

Yeah, let the cattle in for one year and you set back the growth of the woods for twenty years.  Another thing they're doing around here is growing Ginseng in the woods.  This requires removal of all the softwood and the undergrowth.  The space between the mature trees is then cultivated damaging the surface roots.  Yech!  I didn't buy into this, but maybe I should of as the soil here is very rocky with hard pan and I'm getting a lot of die off.  Lot of regrowth of ironwood, though.  Still this area is becoming a bedroom community and there really is no hope for the forests long term.  Land prices are high here too (that's my retirement account).  The bottom line, though, is that anyone considering using their own wood long term should be aware of the fragile nature of the forest.  Treat it right and it'll take care of your needs indefinitely.