How long of a thermowell?

If I wanted to add a thermowell to my brew kettle for a sensor, how long should I get? Should the sealed end be in the center of the kettle? If so, I have read somewhere that the sensor should be in contact with the sealed end of the thermowell. If that’s the case, and I have a wide diameter BK, where do I find a sensor probe that long? Thanks.

This is the thermowell that came on my HLT and MT, only welded, on my MoreBeer sculpture. … ?site_id=5 The probe from a Ranco PID controller fits perfectly of course since they built the thermowell for it.

It is a couple of degrees off from the dial gauge on the MT though. I verified the dial gauge is more accurate using a floating thermometer and a traceable scientific “lollipop” type. Not sure if the PID, thermowell or the probe causes this but once you know how far off it is you can adjust easy enough.

If you are interested I can get photos and measurements on where they placed it. The HLT and MT are 25 gallon SS.

If adding to a brew kettle, I’d get one as short as possible. Less to clean and it won’t interfere as much with stirring. Long or short, the key to getting an accurate reading from a thermowell is liquid movement. Mine may read 170 with still-water/wort, but as soon as the liquid is stirred the temp moves significantly. A recirculating pump helps here to give you an accurate temp.

Just curious, why are you thinking of adding a thermowell to your brew kettle? I’ve got a thermometer mounted on one of the ports for my kettle, but I’ve found it’s one of those not so critical accessories.

I’m thinking about adding a thermowell because I am seriously considering converting to an electric brewing system. Here in Western New York, it is always very windy, and I have a difficult time boiling wort on an open porch. Besides, I can only brew when it’s cold because I am not set up with a fermentation chamber. So it would be nice to bring the wort boiling back in the house and retain all that heat inside instead of having it blow away outside. It’s also a pain carting the kettle in and out of the house several times between the strike and sparge waters and then the full kettle of wort. So I have been researching homemade electric heating element setups, I’m good with electrical wiring, and I can use my kitchen’s electric oven 50amp receptacle to power it. I plan to set up a breaker box I have kicking around with a double pole 30amp breaker for safety. Unfortunately, it seems that the cheapest and easiest option to control this 5500 watt element is with an electronic controller called a PID. I would prefer a rheostat kind of control, but none exist (at least inexpensively) to control such a large electrical draw. The PID needs a thermocouple for temp readings in order to control a relay to then control the heating element. This means I need a thermowell to hook the thermocouple to the kettle. I will start another thread on this at some point. Not sure if this forum is the best one for this discussion. Obviously, I’ve gone on a tangent, but I think this answers your question.

It does answer my question, but if I was you, I’d reconsider using a PID for this application.

PID works well for quickly and accurately bringing something to a target temperature and keeping it there (would be a great way to control an electric heated mash tun), but would have problems controlling a boiling kettle. For boiling, you don’t want to control the target temperature (as long as it is boiling, it is staying stable at the boiling temperature), instead you want to directly control the power as that controls how vigorously the kettle will boil.

If you use a PID and set a target temperature for 212°F, it would direct power to the heater to get there as quickly as it could and then reduce the power to the heater until it was barely simmering - to just the minimum power to keep it from dropping below 212. But if you set it for 213, it would never reach target, and it would slowly ramp up power as it attempted to get to 213 until it was at full power.

This means that with a PID, you can’t control the boiling rate, except by restricting the maximum power available. Which is best done with one of those expensive rheostats. Which means you are better off just leaving the PID out of the circuit entirely.

Thanks, and I totally agree with you. It’s one of my big concerns, and I’m still trying to figure out how exactly I am going to control the boil. Do you have any links to what you think is the best electric brewing setup? Do you use one? I’m definitely planning on making it myself. If I could find a relay that would work with a rheostat at 220v, I would be all set, but all of them work on a 12v switching circuit because they are designed to work with a PID. Electric oven rheostats, called infinite switches, aren’t rated anywhere near the 5500 watts that these heating elements draw. I’ve looked at kiln relays, but the company says it wouldn’t work with the infinite switch without adding some additional equipment. Maybe I’ll investigate this further. Thanks.

Sorry, I don’t use electricity for boiling, so I don’t have any info on decent systems that are affordable. Some day I’ll probably switch, it makes much more sense overall. Perhaps I’ll take a look at what you come up with and try that :smiley:

Sounds like a deal! I’ll keep you posted on any revelations that I might have. Thanks again.

I’m attaching a crude drawing my electric brew system. Hopefully, it will be clear enough to show you how I built my electric system (cheaply).

With a little tinkering it could be converted to a RIMS. I prefer the HERMS because I can keep the wort from over-heating in the heat exchanger coil and denaturing the enzymes; that may be overkill on my part.

My thermowell just lays across the top of or is jammed between the coils of the heat exchanger coil (my immersion chiller) in the water bath.

The SCR is cheap and works great at controlling the boil.


OK, the site refused to load a PDF, a DOC, or a TXT. I’ll try again with scanned jpegs. Nope. The site won’t take a file over 512 MB. I’ll try just pasting in a text file in the body:

STC-1000 ================================ temp sensor inside 1/4 inch ID copper
| | heat relay cool relay
| | terminals terminals
| | | \
| | | ---------------------------120V relay coil of 240V relay
| | | |240V out| |240V in |
| | | | | | from |
| |Hot 120V bus bar----| / | | | wall |
| | / | | | outlet|
|Neutral 120V bus bar–/|----|--------- | SCR |
| | | input |
| | silicon-controlled rectifier
120V in | | (SCR)
from | |
wall | |
outlet | SCR |
| output|
| |
water heater element

The STC-1000 provides a cooling output, but I don’t use it. It might be useful if
you were controlling a chamber that could potentially need both heating and cooling
as the ambient temperature varied throughout the fermentation.

Both the heating and cooling outputs from the STC-1000 are terminated in a standard
wall outlet with a standard three-prong plug and cord leading to the relay coil
connections on the STC-1000. I also don’t show the standard three-prong plug
leading to the hot and neutral bus bars. You could use wire nuts, but it’s not
as reliable or as neat as the screw terminals on the bus bars.

Not shown: the grounding bus bar, but it is a NECESSARY safety feature!

Not shown: the small computer fan under the SCR or the USB power supply
that drives it.

Note that the STC-1000 just opens and closes relays. It does not provide 120V!
It took me a few minutes to figure that out – DOH!


The --/|-- where the hot wire from the wall outlet crosses neutral bus bar is
in lieu of the standard loop where one wire crosses another in a drawing
but does not make electrical contact in an assembled device.

The whole lash-up is mounted neatly (yeah, right) in a large plastic fishing
tackle box. Get a bigger box than you think you could ever possibly need so
you have plenty of room to run your connections and cover the bus bars. I used
wire cut from the end of a clothes dryer cord for all 240V connections. Tinning
the ends of all stranded wire makes connecting the screw-down connectors
easier and safer.

Sorry for the quality of the “drawing”. NB would not accept either a PDF or a DOC.


I used an STC-1000 (under $20.00 from Amazon or Ebay). It’s convenient if you speak metric; my STC reads in Centigrade.

The temp sensor that comes with the STC-1000 is said to be waterproof. I put mine into a thermowell (¼ inch ID copper tube with one end crimped – vice grips – then soldered with no-lead solder.

The “heat” relay of the STC-1000 is wired to the coil of a 240V relay (under $15.00 from Amazon or EBay).

The output from the 240V relay is wired to a silicon-controlled rectifier (SCR) (about $20.00 from Amazon or EBay).

The output of the SCR is wired to the water heater element.



An SCR is NOT a rectifier. It trims a portion of the AC sine wave and produces a similar effect. It will get warm when operating below 50%, but a computer fan powered by a USB power supply (5V, 0.5 amps – yeah, I know the fan is rated at 12V, but the USB power supply fell out first) keeps it cool.

I leave the SCR set to 100% and use the STC to turn a 240V relay on/off to reach and hold the temperature of a water bath (with an immersion cooler in it) during mashing. I use a March pump to circulate the wort from the bottom of the mash tun, through the immersion chiller, and back to the mash tun.

As a side note: I often do step mashes and alternate between using my kettle as an HLT to heat water for infusion, and using it as the waterbath to raise and hold mash temperature. Either way works and I have no idea which makes better beer.

Once the wort is transferred to the kettle, I remove the STC-1000 temp sensor from the kettle so it will keep the 240V relay closed. I adjust the SCR to 30% to 45%, depending on how vigorous a boil I want.

SCR: … +rectifier

240V relay: … 220V+relay

120V hot, neutral, and grounding (not shown) bus bars are from Lowes for about $7.00 each – they’re easier and cleaner than using wire nuts.

For information on mounting the water heater element and a spigot, go to: and … tun?page=3

You do not have to use the VERY expensive punch The Electric Brewery recommends; a hole saw works well if you take it slow and easy and use some cutting oil.

Dan, thank you for the information. I like it! I have a few questions. If I wanted to start very simple, couldn’t I just hook power up to the SCR and then to the heating element? The relay is only needed for the STC-1000, correct? I see that Amazon has a 10000W 220V SCR for sale. If I went that high of a wattage (considering the price is about the same), wouldn’t I be less apt to overheat it with a 5500W heating element?

 Also, could I get away with one of those relay heat sinks to cool the SCR, or do you think I need a fan?  The reason I ask is that I plan to plug my system into my electric range's 50amp receptacle and run power to a small service panel I have kicking around which will have a double pole 30 amp breaker to supply power to the kettle.  The panel will be secured to my brew cart, BTW, and I also plan on having the controls in that panel as there are only spots for breakers on 1 side of the panel for some reason.  Anyway, oven range plugs are 3 wire (2 hots and a ground, no neutral) which means I can't safely create a 120V circuit within my service panel to supply power to a small fan.  If you think I can't reliably cool the SCR with heat sinks, then I guess I'll have to run a 4 wire cable hooked up to a double pole 30 amp breaker in my house's main panel and terminate it to a 4 wire 30 amp drier receptacle in my kitchen.  Not a difficult task, but it is another cost and another thing to do.  

 Thanks again for sharing your setup!

The relay is only for the STC-1000, so I agree, you don’t need the relay or the STC-1000. The higher wattage SCR sounds like a good idea. I think mine is also 10,000 Watts, but I couldn’t find the same model when I looked this time. Using the STC-1000 lets me read while the system brings the mash up to temp and hold temp. Works well for me, but it’s another complication.

Looking at the photos of the SCR I linked to, I see that it has a flat bottom, so a heat sink would work well. Mine has a finned bottom, so I went with the fan - also, I had several fans and power supplies, so the cooling was free. Don’t be discouraged by the descriptions of SCRs and other components that say “220V”; what we call “220V” is actually 240V, but we’ve gotten in the habit of referring to them as “220V” ; maybe it’s because in most of the rest of the world electricity is actually 220V. My “220V” SCR seems happy working with 240V.

I also have a 3-prong outlet (dryer) so I ground through the 120V outlet. You can get 120V between either of the 240V hot leads and the ground. For safety, it might be worth running a separate 120V cord so you can use that ground and have some flashing lights to impress the spectators.

The service panel sounds like a good idea too. I should have done the same so I could have a breaker in there. (Where were you when I was starting this??) It’s especially attractive since there’s room for the SCR and other components you add later.

There are plenty of more elaborate and more automated systems, but if you don’t mind doing some of the processing mentally, I think you’ll like this approach, and the price.

Keep us posted on your system build.


Thanks again, Dan. I sure will post when I got it together!