HomeRoast Digest

Topic: Use a space heater? (35 msgs / 898 lines)
1) From: Peter Bishop
Apologies if this has been done to death already, but like a lot of home
roasters, I can't look at anything without wondering if it could be used or
adapted for use as a roaster :)  So, I was wondering if a propane space
heater could be used as a heat and airflow source for a fluid bed roaster.
The unit I've been looking at (Reddy Heat RLP50VA) is rated up to 50KBTU,
with an internal fan rated at 1/20hp (with a throughput of approx 275cfm).
The idea would be to mount it vertically and attach a conical type roast
chamber above.  If needed, I'm guessing that I could make the airflow
adjustable with a variac.
Targeting a one pound load, is 50,000 btu sufficient heat and will 275 cfm
provide enough airflow to make it all work.  I know there are a few other
variables (chamber design etc), but is this a viable concept?  I'm sure
someone must have tried it... after all, it's a ready made unit that
provides both heat and airflow in what seems to be usable quantities.
Thanks in advance, and apologies if this is a standard newbie question.  I
looked through the archives and nothing jumped out at me.
...needing to roast... but it's raining.
...maybe I'll go to Goodwill instead... I just KNOW they've got a turkey
roaster there with my name on it :)

2) From: Dan Bollinger
John,  The determinate for a fluid bed isn't cfm, but static pressure. The fan
in those heaters is horribly inadequate for lifting beans. Dan
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3) From: Clayton Smith
I've been digging around on the internet since reading your message.  The
couple of owner's manuals for propane forced air heaters that I've been able
to find so far both talk about a "High Temperature Control" at 240 degrees
Fahrenheit.  Unmodified, it doesn't seem that they're set up to provide the
temperatures needed to roast coffee.
Of course, with *lower* air flow.....ok, who's been brave/crazy enough to
"mod" one of these babies?  Variac on the fan motor?

4) From: Peter Bishop
Dan, Thanks, that makes sense.  If I understand correctly, the fan may be
spinning merrily shifting a lot of air, but cannot deal with any significant
back-pressure or resistance.  A motor designed for an application requiring
more torque (or just more powerful!) will provide better static pressure
performance.  I just pulled a motor (marked 2.3amp, 1000rpm) out of a old
bread maker... I'm not saying that would do the job, but it would certainly
be designed for something a little more testing than just shifting air.
That being said, the turkey fryer burner is looking like a good place to

5) From: Tom Ulmer
i'm thinking there certainly must be a way to (re)configure the fan blade
arrangement and discharge to provide adequate lift. seems like the motor and
heat source could handle the change.

6) From: Dan Bollinger
John, I don't believe a propeller type blade can ever be spun fast enough to do
what it is you want it to do. You need a centrifugal blower. A single stage is
sufficient. For a 1-5 pound hot-air roaster I think the Graingers Dayton 7D747
is in the ball park, but I can't say for sure because no one has tried it yet.
Danhttp://www.grainger.com/Grainger/productdetail.jsp?xi=xi&ItemId11729831&ccitem=It is available with a 120VAC motor, too.
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7) From: Dan Bollinger
Tom, If you can change out the propellor blade for a centrifugal blade running
inside a casing (housing) it would work, but I'd think this would be more work
and trouble than simply buying a good blower.
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8) From: Peter Bishop
Logically, either replacing the fan with something beefier, or applying an
external air feed would negate the underpowered fan.  I was exploring the
idea of using an "off-the-shelf" item that seemed to be available for about
$70+... and could actually be used to heat the garage in the winter!  If I
can get one cheap (yard sale etc) then I'll happily pull it apart, but I
don't particularly want to buy a new one just to rip it apart :)  The
Goodwill turkey burner and blower seem to be an idea to play with. The
downside of using one of my blowers and suitable ducting (as far as I can
see) is the noise factor.

9) From: Tom Ulmer
indeed. i have seen some variable speed air movers that would be perfect.

10) From: Dan Bollinger
Peter brings up an important issue, blower noise. I think a lot of the noise is
coming from universal AC/DC motors, the type with brushes. The Dayton blower is
an induction motor, so the only noise is coming from the blower, which is rated
at 74dB.
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11) From: Ed Needham
Sealing all the air leaks, and adding a fan that can actually lift beans in a
static situation, or add a bit of mechanical agitation, and you might have
something.  Might even have to reduce airflow to get the temps up.
I do think the mechanism of air and a flame is a workable concept to start
At least it is a ready made testbed.
Ed Needham
To Absurdity and Beyond!
"Nunc Aut Nunquam"
homeroaster ... d.o.t ... com

12) From: Ed Needham
I think so too.  It would involve a closer tolerance cowling around the fan
blades, so there is a minimal amount of reverse blowby when under pressure.
Possibly adding a second fan, and sealing all the places where it can lose
pressure.  Beefing up the horsepower of the fan, so it doesn't bog down under
pressure.  Maybe re-configuring the pitch angle of the fan blades so as to
have more thrust and less CFM (like a prop adjustment on an airplane-low
pitch for power climbing and higher pitch for speed).  That would increase
the heat too.
Ed Needham
To Absurdity and Beyond!
"Nunc Aut Nunquam"
homeroaster ... d.o.t ... com

13) From: peter zulkowski
Hi Peter,
You and I should get together. This week I picked up a Craftsman leaf 
blower vac which seems pretty keen, and today I picked up one of those 
aluminum wine chiller things that you see in fine restaurants. Holds 
like maybe 2 1/2 gallons. The way I see it I can hook my leaf blower on 
the back end of your heater and then force the resultant through some 
slots cut into this bucket, maybe with a  SS mesh on top to hold it all 
together and keep the beans in, and we uns can do some serious (?) 
roastin (grin)
Can't help it, still want to roast a lot at once for cheap :O)
Peter Bishop wrote:

14) From: prentice
Quoting Ed Needham :
Sounds just like my gas dryer.  And if you're looking for lift, might I suggest
a regenerative blower.  Spencer makes a good one.
This mail sent throughhttp://www.snailmail.ch/

15) From: Dan Bollinger
Regens will certainly work, but they are more expensive than a simple centrifugal
blower. They may be able to handle recycled hot air.
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16) From: Gene Smith
prentice writes:
What is a 'regenerative blower' please?
Gene Smith
riding the wild learning curve, in Houston

17) From: Dan Bollinger
http://www.grainger.com/Grainger/productdetail.jsp?xi=xi&ItemId11777528&ccitem=Here is an inexpensive one, only $560.  It's a vacuum/blower/heater.  Yep, it
even heats the air by friction alone.
go tohttp://sweetmarias.com/maillistinfo.html#personalsettings

18) From: Angelo
"Mechanical agitation"....hmmmmm...  Like the auger of the Zack & 
Dani?...I'm surprised no one except Z&D, as far as I know, has seen fit to 
use this concept in roasting. You can have fluid and conduction roasting at 
the same time, and you can control the ratio by the diameter of the auger 
vs. the area around it...It would also allow one to use a stationary 
vertical chamber over the heat/air  source, with  the auger turned by a 
spring(or other)-driven motor.  Just ruminating... :-)

19) From: prentice
Special type of blower capable of producing respectable amounts of pressure (or
vacuum).http://www.spencerturbine.com/Vortex/introduction/vortex_story/principle.htmlwill explain it all much better than I can.
And yes...certain types of these can handle the recycled heat.
Quoting Gene Smith :
This mail sent throughhttp://www.snailmail.ch/

20) From: prentice
I believe that typically the temperature rise depends upon the amount of
backpressure in the system.  I COULD be wrong...but when was the last time THAT
happened?  ;)
Prentice (just kidding!  Really!)
Quoting Dan Bollinger :
This mail sent throughhttp://www.snailmail.ch/

21) From: Peter Bishop
Thanks to all for the comments.  It made me realize that I've a big gap in
my knowledge when it comes the technicalities of airflow, static pressure
etc.  I've done a bit of reading and research, and I *think* I understand
the issues a bit better now :)  There's a Grainger at the end of the road
where I work... I think I know what I'm doing at lunchtime. :)  Not buying,
but just having a hands-on to see what's what.

22) From: Lowe, David
I have to believe that for the sort of pressure that is needed for =
roasting that a propeller blade would be possible, though maybe not the =
easiest to design/manufacture. The compressor section on a jet engine =
can achieve significant pressure from multiple stages of blades and =
turning vanes. Not as simple as a single stage centrifugal blower =
Dave Lowe

23) From: Dan Bollinger
I have to believe that for the sort of pressure that is needed for roasting that
a propeller blade would be possible, though maybe not the easiest to
design/manufacture. The compressor section on a jet engine can achieve
significant pressure from multiple stages of blades and turning vanes. Not as
simple as a single stage centrifugal blower though.
Dave Lowe
Dave, From what I know, both are axial flow pumps and the similarity ends there.
Jet engines use turbine blades. It is not uncommon to see turbine blades where
the blades cover more than 100% of the disc. Compare that to your typical fan
blade where the blades cover about 50% or less of the disc. Turbines benefit from
multiple stages each using stator blades, too, but I've never heard of increasing
the pressure with multiple fan blades. I've never seen them used in stages,
either. Dunno why, but perhaps there is a reason?  Dan

24) From: Peter Bishop
The discussion is dove-tailing nicely into my new found area of study :)  I
looked at the speadsheet on Ed's site (Alchemist John's spreadsheet), and if
I read it correctly, to keep 500g of beans moving (in an eight inch
chamber), I'll need at least a half inch of static pressure with a cfm
approaching 50.  Current thinking is that something like a Dayton 4C447
(quoted as 135cfm @ 0.5in) should be more than enough to do the job without
breaking the bank ($66).  I've just obtained a 185,000 burner (with
regulator) for $20, so this may be the direction I take... pretty much the
same way that Ed has half-built at the moment (Ed, any more news?).
I feel a bit of a fraud... the original space heater I was looking at was
the Reddy Heat RLP50VA.  It was listed at Lowe's for $69.50 (which seemed
like a deal).  It's marked as unavailable, and everywhere else is a LOT
higher (over $100 more).
It's like the old story...
I'll have one of those please...
      That'll be $175 please
But it's only $69.50 down the road!
      I suggest you get it from them then.
They're out of stock...
      Well, when I'm out of stock they'll be $69.50 as well

25) From: Johnny Kent
Hi peter,
That may be so that you need only 0.5 to  keep the beans moving but you'll
probably need more than 0.5 inch WC to get them moving in the first place.
I don't recall if that spreadsheet gives the statin pressure needed to get
them moving? Probably not a whole lot if they are spread across an 8 inch
 I can happily roast 13.5 oz greens (and it could do way more but the
chamber's limited) with a heat exchanger in my 35,000 btu charbroil BBQ so
185,000 btu should roast plenty more than 500g. Room to spare.
Also note that HD carries a 135,000 btu turkey frier for $49.99 (reg but no
tank) looks a lot like the one on its side at coffeewisdom.
Johnny "in unseasonably hot San Diego" Kent
At 06:19 PM 3/9/2004 -0500, you wrote:
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26) From: Ed Needham
I've seen a few dual stage axial fans on Ebay.  Seriously considered grabbing
one (not by the spinning blades) as a roaster air mover, but never got high
bid.  Those things sell pretty high.  I think the ones I've seen might be
military surplus.  They kinda have that look.  At least they are industrial
in nature and not Wal-Mart plastic.
I may get one yet...
Ed Needham
To Absurdity and Beyond!
"Nunc Aut Nunquam"
homeroaster ... d.o.t ... com

27) From: Ed Needham
I add to this thing a little at a time.  One day, before I get too old to
operate it, I'll finish it.  I've been so taken with grill drum roasting that
air roasting in one or two pound batches is less attractive.
My next step is to fabricate the stainless cone top for the heat chamber,
where it connects with the roast chamber (almost finished).  Since I don't
weld, I'll have to job that one out to a local fabricator...right after I
finish another 5 pound drum batch .
(psssst...do you realize that most houses are heated with less than 185,000
BTU furnaces?  You sure it has that much output?  Mine is 79,000 BTU, and is
taken from a turkey fryer.)
Ed Needham
To Absurdity and Beyond!
"Nunc Aut Nunquam"
homeroaster ... d.o.t ... com

28) From: Brian Hyde
http://www.homebutcherplus.com/t/Turkey-Fryers/26-Qt-Turkey-Fryer-Kit-B0000CBJAX.htmThis is the typical burner made by fusion metals.  It's listed both as 
170K and 175K.  
The jet style burners might list to 185K.  I can't remember.  I don't 
look at those that often because the footprint on the bottom of the 
kettle is too small.  But for this purpose who cares.  
Ed Needham wrote:

29) From: Peter Bishop
I went to the Barbour International site (which leads directly to Bayou
Classic).  The SP-10 ($45) looked to be the best option as it included the
regulator etc, then I noticed that the SP-30 is listed as the same, but
without the wind shield.  It was marked as "promotional", and the price was
$19.95.  Elsewhere (Ace Hardware), the SP-10 output is listed as (up to)
185,000 btu, which I agree seems a little excessive when compared to a
domestic central heating system, but I thought it better than getting
something borderline or underpowered :)  $20 for a new high-output burner
with regulator, hoses etc seemed reasonable to me, and less of a hassle than
hitting ebay.
Now I get to put my suspect metalwork skills to the test!
Reference Links:
Bayou Classic SP-10http://www.bayouclassicdepot.com/product_311.htmAce Hardware SP-10 btu detailshttp://www.acehardware.com/product/index.jsp?productId35083&cp55113.1260252&parentPage=family<Snip>">http://www.bayouclassicdepot.com/product_309_detailed.htmBayou Classic SP-30http://www.bayouclassicdepot.com/product_311.htmAce Hardware SP-10 btu detailshttp://www.acehardware.com/product/index.jsp?productId35083&cp55113.1260252&parentPage=family<Snip>

30) From: Lowe, David
Looking at the pictures/descriptions it isn't clear to me whether or not =
you can throttle the burner. Never used one or looked closely at one, =
but it would seem like an important feature for roasting.
Dave Lowe

31) From: Peter Bishop
I'm assuming the venturi and/or regulator & valve will provide some control
over heat output... this may be an incorrect assumption on my part, but I'd
taken it for granted that any burner like this (as long as I leave the
as-supplied controls intact) would offer variable control rather than just
an on/off setting.  That being said, my only experience with propane up to
this point is cooking the usual burnt offerings out on the deck with a
standard BBQ set-up.

32) From: Dan Bollinger
There is a valve near the regulator on the unit. If that doesn't work well for
control you could always add a needle valve.
Looking at the pictures/descriptions it isn't clear to me whether or not you can
throttle the burner. Never used one or looked closely at one, but it would seem
like an important feature for roasting.
Dave Lowe

33) From: peter zulkowski
Hi Peter,
Thank you very much for the info on this.
Do you know if the burner is cast iron? If it is I will sure order one.
Back when I was a youngster learning to weld in Louisiana, the guy I 
worked for was having me make these. The burners were cast iron, and he 
insisted you did not needed a regulator for it. Adjust the flame with 
the valve on the tank! We did just that and it worked fine. The tank got 
cold though; and it was pretty loud.
Looking for a cast iron burner, here in LHC.
Peter Bishop wrote:

34) From: Peter Bishop
I'd assumed that the control would be via the valve and /or the venturi.  It
should be here soon(ish), so I guess all will be revealed when I incinerate
the garage :)  Seriously... I'll report on what it is and how well it
responds to the various controls.  There was also a question (from PeterZ)
as to what the burner head itself was made of (was it cast iron)... I'd
assumed it was cast aluminium, but we know what happens when you assume.

35) From: Ed Needham
Those must be pretty intense burners.  Wow.  Make it so, captain!
Ed Needham
To Absurdity and Beyond!
"Nunc Aut Nunquam"
homeroaster ... d.o.t ... com

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