Thread: Shed heating options

Originally Posted by jack620

Eskimo,
I'm no expert in the area, but my understanding is that the efficiency of heat pumps drops as ambient temperature drops. In Canberra, where it regularly gets below 0C in winter, they spend a significant amount of time and energy defrosting their coils. At what ambient temp were the figures you quoted measured?
Chris

all manufacturers quote nominal heating capacities at 7C

take the Hitachi nominal 7kw heating/cooling wall split....on heating mode and at 7c it puts out 8kW...
at 0c it is 7kW.
at -5c it is 5.7kW
as you can see heating output capacity does drop away at lower ambient temps, but as the unit uses less input power at lower ambients say 0C, the cop's would still be around very high eg +2.5...this is still more than double the heat than from electric elements

these figures must also take into account defrost cycles...the new Meps regs has assured us of the fact that manufacturers can not cheat

Originally Posted by A Duke

I personally would would worry about dust and fumes being sucked into fan heaters and getting onto the elements and/or blocking the screens.

Bob, 14 to 17 C have been our maximums the last few weeks with -5 the low. We have known -10 (well within a couple of decimals.)

Regards

I want to live in the act you are in!
Granted today was real nice once the fog lifted, but my van thermometer hasn't registered above 13 all week. That's mostly tuggers though......
My fire is on now, just beut, warm and cozy......the kids still want to run around outside in the cold while there is still light though..

Originally Posted by Ueee

I want to live in the act you are in!
Granted today was real nice once the fog lifted, but my van thermometer hasn't registered above 13 all week. That's mostly tuggers though......
My fire is on now, just beut, warm and cozy......the kids still want to run around outside in the cold while there is still light though..

I did not say every day and I think your van is about right for this week.
Regards

Originally Posted by 19brendan81

"Any chance you can run a mains gas pipe to the shed? How far is the shed from the nearest gas pipe on the house?"

About 1 meter...

In that case I would get a quote for having a gas outlet put in the garage. Actually, I would run the pipe myself, but don't tell anyone.

Originally Posted by eskimo

personally, I have a 4 panel suparay.....and for info only, these dont heat the air directly..they work by the items eg lathe, mill, and other stuff in your shed absorbing the infrared rays and then those items release that heat back into the space by convection.

Hello,

Am intrigued - is this an expensive toy ?

Off to do some googling ...........

Bill

After seeing Ueee's diesel furnace heater that he recently scored and the amount of heat that diesel heaters can put out versus their running cost, Id be keen to look at something like that!

Living near Melbourne, my main complaint about this time of year is if I am trying to paint any pieces of machinery. Turns out crap and takes weeks to dry.

Mind you, I like that rocket wood heater too!

Simon

I had a look at a couple of rocket heater video clips and I'm having trouble working out "how they work".

A strong draft like that is great for getting (and keeping) things burning but it's also going to be sucking a lot of hot gas right up the flue. One video showed someone making one from an old air cylinder ended up with the cavity between the fire box and the outer skin being filled with foam insulation. I can understand insulating if you wanted to reduce the amount of heat escaping from the firebox (especially if you were heating water tubes or something), but the idea of a fire is to warm up the surrounds.
It seems that the heat is mainly being passed to the environment from the flue via conduction rather than radiation & convection from the fire box as well. The slow combustion heater or pot belly would be a more efficient option I think - rocket heater looks to me to be not much better than a small open fire place. Yes, it heats but does not seem to be a great leap forward in efficiency.

Michael

Originally Posted by Michael G

I had a look at a couple of rocket heater video clips and I'm having trouble working out "how they work".

A strong draft like that is great for getting (and keeping) things burning but it's also going to be sucking a lot of hot gas right up the flue. One video showed someone making one from an old air cylinder ended up with the cavity between the fire box and the outer skin being filled with foam insulation. I can understand insulating if you wanted to reduce the amount of heat escaping from the firebox (especially if you were heating water tubes or something), but the idea of a fire is to warm up the surrounds.
It seems that the heat is mainly being passed to the environment from the flue via conduction rather than radiation & convection from the fire box as well. The slow combustion heater or pot belly would be a more efficient option I think - rocket heater looks to me to be not much better than a small open fire place. Yes, it heats but does not seem to be a great leap forward in efficiency.

Michael

Hi Michael,

I have been trying to work out the theory behind them as well. The few youtube vids I saw of them described them as being "extremely efficient" wood heaters but I tend to agree with you. I thought you would want some sort of baffle system inside so that the gases impart some of the energy in the form of heat to the heater before disappearing up the flue. Unless as you say, that the flue is the integral part of heating the room via radiant heat.

Cheers,

Simon

I was also at a loss to understand these heaters considering the poor examples shown on YouTube but I found one video that seems to explain it fairly well. I am not saying they are a good thing yet but at least they look feasible.

Do a search for "The principals of a rocket stove and how to build one" on YouTube.

Some of the examples I saw looked just like a minature fireplace and chimney but once you watch this video at least you will know what is meant to be happenning.

I would like to try one but I am pretty busy so will not get a chance for quite a while. If anyone else attempts this.... well you know.

Dean

I think there is more than one "rocket". The idea behind insulating the fire box is to get better combustion. You then use a long flue to radiate the heat.(or a big lump of concrete as thermal mass) There is a problem with condensing flues though...... what do you do with the condensate? I'm lead to believe its not very nice stuff, but they seem to say that about most thinking these days.

Stuart

Originally Posted by Oldneweng

Do a search for "The principals of a rocket stove and how to build one" on YouTube.

Well, that video did explain a little more of how they are supposed to work. The idea of using the flue gases to do extra work seems more sensibe. It reminds me of a stove design that was used by Mawson -


So - the "pretend" rocket stoves keep the flue gases hot and rely on the flue to radiate out the heat (and probably waste a fair bit in the process) while the proper ones run those flue gases past a basic heat exchanger to try and extract additional heat from the process. The key measure of success would seem to be the exhaust output temperature. If it is low enough then a reasonable efficiency could be assumed. Having read about some of the design principles used in slow combustion stoves I don't think these would necessarily be anymore efficient than a good SCS. Their main attraction would be that they can be made by an average person from recycled or cheap materials. While the video showed one being almost thrown together I'm guessing that there are dimensions and ratios in there that will affect efficiency dramatically as well.

Michael

Just an option for you - I noticed someone in Canberra is selling the Jetfire heater Jetfire Gas heater 25A | Other Tools & DIY | Gumtree Australia Tuggeranong - Banks
(i do not have any affiliation with the seller)

Originally Posted by Michael G

Well, that video did explain a little more of how they are supposed to work. The idea of using the flue gases to do extra work seems more sensibe. It reminds me of a stove design that was used by Mawson -

snip

So - the "pretend" rocket stoves keep the flue gases hot and rely on the flue to radiate out the heat (and probably waste a fair bit in the process) while the proper ones run those flue gases past a basic heat exchanger to try and extract additional heat from the process. The key measure of success would seem to be the exhaust output temperature. If it is low enough then a reasonable efficiency could be assumed. Having read about some of the design principles used in slow combustion stoves I don't think these would necessarily be anymore efficient than a good SCS. Their main attraction would be that they can be made by an average person from recycled or cheap materials. While the video showed one being almost thrown together I'm guessing that there are dimensions and ratios in there that will affect efficiency dramatically as well.

Michael

"Pretend"? Not a good name for them I thought.

It is supposed to be the sharp bends that improve the efficiency.

"The key measure of success would seem to be the exhaust output temperature."

I would agree. I did see one document showing a built in design for a geo dome which had lots of options for heat removal including 6 heat tubes coming up thru the floor. The exhaust temp was quoted for this design and was very low, but this was a lot more than a heater for the shed.

I am still waiting for details of construction and test results from a forum member.

Dean