Author Topic: workshop heating (Read 16583 times)

shipto · « **on:** October 14, 2013, 06:08:51 PM »

I can put it off no longer so I nipped to our local B&Q and picked up a garden burner. (pic 1)
The plan is to place it outside the workshop and fit a heat exchanger to draw warm air into the shop thus the fire will not be endangering my shop.
So I took 2 plates and marked and drilled 9 holes then plama cut the holes for the exchanger tubes using a simple circle jig. Then it was just a case of welding in the tubes and that how far I got today.
Now here I would like advice should I flue around or through the pipes? the origional plan was to mount the exchanger with the pipes horizontal and the flue would be going around the outside of them but as luck would have it the 9 tubes equal around the same area as the hole in the top of the burner. so the question is do you think the unit would be more efficient drawing air through the pipe or from the area around them?

vtsteam · « **Reply #1 on:** October 14, 2013, 08:01:23 PM »

I'll vote for around them because you'll increase turbulence of the hottest gasses. But you'll need to box it in and insulate, and also make it accessible for cleanout. The more heat you extract, the more you will collect ash and creosote because you'll cool the smoke in contact.

shipto · « **Reply #2 on:** October 15, 2013, 05:18:07 PM »

thanks vtsteam I am going to box it in but havent got to that part yet. However you mentioning creating turbulance gave me an idea, so I have placed a plate on the top layer of pipes right in the middle. The reason being that now none of the hot gasses from the fire will be able to go up the chimney without hitting some part of the heat exchanger on its way out.

vtsteam · « **Reply #3 on:** October 15, 2013, 10:17:57 PM »

Baffles are good, they increase residence. You can use more than one if you alternate them. Since you have a central one at the top, the next row down could have two side plates with a central space, etc. More complexity, though does increase clean-out difficulty. Everything is a compromise.

btw it's tough making tube plates. You did a good job with thin stock there

shipto · « **Reply #4 on:** October 16, 2013, 12:53:03 PM »

Quote from: vtsteam on October 15, 2013, 10:17:57 PM

btw it's tough making tube plates. You did a good job with thin stock there

I wont show you the other side where the tubes stick out by 30mm then

not pretty.

shipto · « **Reply #5 on:** October 16, 2013, 03:34:33 PM »

todays progress:
cut the rest of the plates and started to weld them together then ran out of gas for the mig welder

.
I dug out my old hobby arc welder and did a few practice welds but decided I wasnt confident enough in the rather rubbish unit, The (probably) damp rods and the fact I havent touched a arc welder for donkeys years, to carry on. so I will wait until I get some more gas friday probably.
Being the impatient person I am I tried a test burn with some kindling and have to say I was pleased with the heat that even this small fire put into the exchanger.
edit: sorry for the big pic have replaced it with smaller one.

RossJarvis · « **Reply #6 on:** October 16, 2013, 05:22:34 PM »

It might be too late, or just stoopid, but could you put fins on the pipes or maybe get perforated mesh in there, contacting the pipes to increase the surface area further? A bit like an old Scammell radiator.

shipto · « **Reply #7 on:** October 16, 2013, 05:41:56 PM »

not stupid at all but yes its a bit late for fins now and I dont have any perforated plate. I am following the advice of vtsteam and putting a access panel on front so might be able to add more metal to soak heat if needed later.

vtsteam · « **Reply #8 on:** October 16, 2013, 07:41:21 PM »

You don't want to restrict the exhaust too much, and clean-out becomes a problem with small stuff. A few nice big baffles with big spaces to let the smoke travel are helpful, and can be more easily cleaned.

In something this small, fins won't work well if too thin. The heat may be picked up on the broad surfaces, but then must travel through a thin cross section to reach the pipes. The thinner the cross section, the slower it travels. Mesh or thin sheet metal would provide little assistance to heat transfer to the pipes unless there was a very large number of them -- as on a baseboard radiator pipe or car radiator. A few won't do much. And they are hard to fabricate and very difficult to clean where used with a wood fire which produces tars and ash in the smoke. They soon build up an insulating layer and become ineffective.

shipto · « **Reply #9 on:** October 19, 2013, 07:13:09 PM »

So got more gas and cut the access panel out of the front and welded it to the exchanger along with the ends and the air pipes.
I will get the access panel sorted tomorrow and if the rain holds off I can sort out where it is going to sit.

vtsteam · « **Reply #10 on:** October 19, 2013, 08:52:40 PM »

Looking good!

And green leaves on the trees, no less... they've all turned color and most are fallen here. I haven't even started a shop heater yet. But split two cords of wood so far.

shipto · « **Reply #11 on:** October 20, 2013, 01:52:29 PM »

Not for too much longer vt they are starting to turn now so wont be long and it will all be bare.
today I:
sorted a place for it all to sit.
sorted out the access panel.
Painted the exchanger with stove paint.
and for my day off tomorrow I am going into work to make use of the plasma to cut the bottom from the chimenera to save me have too much trouble clearing the ash out. Tried with a jigsaw but would have took ages.

shipto · « **Reply #12 on:** October 21, 2013, 10:45:48 AM »

It works and works well

I know its a bit lop sided but the ring which has fitted well all the way through decided it didnt want to fit but I was on my own and it took a lot of effort to get it in place so didnt want to take it of, I will let it cool down and get my mate to give me a hand to fit it properly.
I temp fitted the fan blowing air into the exchanger with cardboard and tape and let it rip and it works very well the flue pipe arrived today as well and I have started to make the fittings for that.

vtsteam · « **Reply #13 on:** October 21, 2013, 12:36:39 PM »

Looks good!

The door vent looks huge -- will you be modifying or fitting a solid door with adjustable vent(s)?

As it is, it will draw in excess cold air, and at full burn might make for a cooler heater than a slower burn would provide.

Other suggestions:

If you could put a second skin over at least some area of the outside of the firebox case and draw combustion air through that before going through a vent into the fire, it would pre-heat it, as well as utilize some of the large radiant heat losses that the firebox will have .

This is all icing on the cake for your more moderate climate probably, but around here it would probably be necessary.

shipto · « **Reply #14 on:** October 21, 2013, 04:23:59 PM »

Thanks vt I did think about a solid door with breather holes but not sure now. A slower burn would be nice however I think I went a bit too far with the hole in the bottom to clear the ash I think I will have to replace it with a removable plate.
As far as preheating the combustion air I dont think its needed when it puts plenty of heat into the shop as it is.

vtsteam · « **Reply #15 on:** October 21, 2013, 09:12:39 PM »

Quote from: shipto on October 21, 2013, 04:23:59 PM

As far as preheating the combustion air I dont think its needed when it puts plenty of heat into the shop as it is.

That's great! Good feeling to be able to work through the winter, and creating your own stove is very cool!

shipto · « **Reply #16 on:** October 22, 2013, 05:14:45 PM »

Put the plate over the hole and started it tonight and it burns lots slower and still puts plenty of heat into the shop.
If there is one quibble the heat is very dry (if that makes sense) and dries the throat a little but nothing plenty of tea wont solve.

awemawson · « **Reply #17 on:** October 22, 2013, 05:28:30 PM »

Make sure that dry throat isn't escaping fumes you are breathing

shipto · « **Reply #18 on:** October 22, 2013, 06:08:28 PM »

Its a thought and I will get a carbon monoxide detector but I dont think it is fumes I made double sure that the tubes and case was sealed, it could be some fumes are coming from the gaps in the eaves as I didnt get chance to add the rest of the chimney. The shed is at the moment well ventilated as I havent got around to plugging the gaps at the eaves and there is no other signs. I have experienced low level fume inhalation before from a boiler that the council appointed repairers insisted was ok 5 times until i got my wifes compact mirror and checked the back and saw the flue was rotted away so bad you could see the flames in the boiler, words where said

vtsteam · « **Reply #19 on:** October 22, 2013, 11:01:48 PM »

Pretty hard to miss wood smoke fumes if they are coming into the shed. It's not like most other combustion exhausts which are more or less odorless and colorless. And a smoke detector does a good job of letting you know if there is a leak if you don't notice, so a monoxide sensor may be superfluous. Plus a smoke detector can also warn you of a fire, which is a more frequent hazard with a wood stove.

And yes, an external wood stove hot air system will definitely dry your house or shop out. It raises temperature at the lower relative humidity level of ambient air, thus drying it out substantially. In winter at freezing temperatures, the air is normally low in humidity anyway. So it dries it even further.

On the bright side, It's a plus for preventing rust on machines. But not so good health wise.

Most people with wood stoves put a kettle of water on top of it to help humidify the air. I'm sitting in front of one now as I write this. Adding humidity to vented hot air would be harder, but not impossible. In deep winter where the indoor humidity can reach as low as 25% here, we not only use a kettle, but also a humdifier running 24/7. That often only brings it to 40%, which is still low, but better.

Pete W. · « **Reply #20 on:** November 05, 2013, 03:34:45 PM »

Hi there, all,

I don't want to 'rain on anybody's parade' but I feel the need to make an observation about workshop heating.

The point is that even if a room is filled with comfortably warm air, an occupant will still feel cold if the walls are cold. It's all to do with the balance between the heat that the body loses by radiation to any cold surfaces (i.e. < 98.4° F) and any heat it receives by radiation from any warm surfaces (i.e. > 98.4° F). (By 'radiation' here, we're talking about infra red, nothing to do with Geiger counters!)

Of course, if you go on heating the air for long enough that air will, in turn, warm the walls but that can be a darn slow process. Better to supplement the warm air source with something that radiates infra red energy. If the IR source is warm enough, it doesn't have to have a lot of area to balance the effect of the cold walls. I'm planning to use an electric tubular greenhouse heater in my workshop. A quartz tube infra red bathroom heater would probably be over-kill for a small workshop, it would need a lot of space around it and protection from inflammable dust.

Of course (again!), the infra red source will also warm the walls as well as the shop occupant(s) and will do it faster than transfer via warm air.

The old 'pot-bellied' stoves are sources of both warm air AND infra red.

awemawson · « **Reply #21 on:** November 05, 2013, 03:59:17 PM »

"The old 'pot-bellied' stoves are sources of both warm air AND infra red."

Also EXCELLENT for toasting crumpets on a cold winters afternoon for tea

vtsteam · « **Reply #22 on:** November 07, 2013, 04:05:07 PM »

But if there's no room for one, since woodstoves require substantial clearance to combustibles, and you want to burn wood, an external furnace is the alternative.

Radiant heat can be produced from an external furnace if desired at the delivery end, via a radiator. While they are usually associated with hydronic systems, there is no reason a hot air heated radiating surface couldn't be built. A thin sheet metal baffle painted black would heat quickly and radiate heat. So would the hot air duct system if exposed.

shipto · « **Reply #23 on:** November 07, 2013, 05:52:04 PM »

I assure you Pete with a good blaze going in the chiminea the heat put out is plenty, you do need to get a good blaze to start but once that has burned down you just need to keep it going at a lower burn rate to keep the shop feeling warm.

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Author Topic: workshop heating (Read 16583 times)