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PostPosted: January 9, 2019, 11:45 am 
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Location: West Chicago,IL
I have an old electric heater of ~ 5.7KW. It will warm up and keep my garage warm in the coldest winter days here. It may take a few hours. It was rescued from a junk pile years ago and I put it back into service about 10 years ago. It is run on 240V by a cord plugged into a dryer outlet. I added a 240V baseboard thermostat mounted to the side when installed it. The minimum setpoint is 50 degrees, way too high. I end up unplugging it when I don't plan on working in the Garage.

I would like to add a normal wall-type thermostat. To that end, I am adding a 24V control transformer and a 24V DPST relay to power the 240V internal contactor.

I am looking for recommendations for a 24V thermostat with a low minimum setpoint hopefully around 32 degrees but certainly no more than 40deg F. I think an electronic version may prevent the radio interference from arcing contacts or chattering relay prevalent in my current system when trying to shut off. That can't be good for long life. It would also be nice to have wifi capability so I can turn it on/off from my recliner. :roll: But that isn't a necessity.

Anybody have one that they can recommend? I am not opposed to lightly used thermostats that have <40 deg setpoint If I can buy on eBay. I've done some research. It seems that "min setpoint" is not a common published spec.

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PostPosted: January 9, 2019, 12:34 pm 
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This doesn't satisfy your ask, but I wonder about a near 32F set-point. I use a standard 50F minimum thermostat in my workshop (oil forced-air heat). I turn the heat up to 60F when I work in there, or even 65 or 70F if I am doing some epoxy work. On that basis I use about 700 litres of oil per heating season. Say $550CAD

If I had a different thermostat I would go lower for unoccupied times, but at anything less than 40F I be worried about freezing in cold spots. Big temperature swings might raise issues with relative humidity changes and condensation.

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PostPosted: January 9, 2019, 1:16 pm 
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Warren, Points well taken. In my case, I'm not concerned about things freezing or humidity in the garage. I just looked at my smart meter bill from yesterday. $2.75USD in electricity cost for 6 hrs of heating on a particularly warm day in January. It ran about $0.31 per hour once up to temp. On colder days it would be higher cost for sure. The lower I can keep the unoccupied temperature, maybe I can consider running it full time(ish). In the meantime, I think it would be on and off periods regardless of the lower setpoints. That is why I was thinking WiFi. I'm basically lazy. But I'd like to try a 32 low setpoint if possible to see what the cost for a baseline is.

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PostPosted: January 9, 2019, 2:37 pm 
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Joined: January 31, 2012, 12:49 pm
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Location: Louisville KY
Oil burner using recycled oil, using an on/off switch?

With the garages I've owned, once the concrete / blocks get cold, it takes about a week to warm the place up. It's like the concrete just soaks it up. Best I could hope for was warm air blowing my direction and some thick padding on the floor.

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PostPosted: January 9, 2019, 3:45 pm 
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Hey Chuck

I ran into the same issue although I heat the shop with natural gas. Where to get a thermostat with a low end set point.

What I ended up doing was using a mercury bulb thermostat https://www.ebay.com/p/Honeywell-T822K1042-Mercury-Thermostat-24v-35-85f-Heating-Only/1900169049.

Now normally these are mounted level to horizon on the wall for accuracy of the set point and and actual heat scale. What I did was tilt the thermostat off level to lower the bottom end set point. It takes a bit of fooling around to get it where you want, but I can set my shop temp as low as 36*F if I want using a regular wall thermostat. Simple.

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PostPosted: January 9, 2019, 5:21 pm 
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Hey Perry, I thought about tilting a mercury stat like you describe. It may have been my fallback choice.

I just found this one that seems to fit my requirements (except for the WiFI of course)

https://www.pro1iaq.com/images/700Manua ... ALitho.pdf

It is the lowest setpoint range that I have found, from 25°F to 90°F (-4°C to 32°C) while operating down to 20F. I've never seen my garage below about 26F IIRC.

It is powered by both 24V and a battery for backup. For about $10 more that the Honeywell you suggested, I'm gonna give it a try.

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PostPosted: January 10, 2019, 9:53 pm 
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I found that 5 C/41F is a good temp to leave it set at ( when not in use ) for my location.

A cheap ceiling fan, running 24/7 evens out any cold spots.


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PostPosted: January 15, 2019, 8:15 am 
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There are tons of products out there to do this; some under $20. No need to limit your search to residential controls.

https://store.solutionsdirectonline.com ... c1744.aspx

https://www.amazon.com/dp/B011VGASLW/re ... 178c75a502

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PostPosted: January 15, 2019, 1:01 pm 
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If you want to go way overboard for no good reason, I grabbed a Honeywell RTH6580WF used on eBay for under $50. Its minimum setpoint is 40 degrees (I usually keep it at 45) and is controllable via wi-fi, so I can fire it up from my phone and by the time I want to go out there it's a balmy 55 degrees. Also it integrates with Alexa so I can just yell at my garage to heat up and it does.

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PostPosted: January 15, 2019, 5:11 pm 
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I live in a climate where freezing isn't an issue, but thought that my solution is kinda cool. I use a RF switch to turn on the garage (outside) lights. I also have an additional relay on that circuit that powers the heater circuit. So if the garage lights are on, the heater is being run by a simple snap-action thermostat. That way I can pre-heat the garage, and never forget to turn the heater off, because the lights serve as a reminder. During summer, I just turn the thermostat down.


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PostPosted: January 15, 2019, 7:05 pm 
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I finished the install an hour ago. The control xfmr is mounted outside the heater thru the wall. It powers the Pro1 thermostat and a 24v relay controlling the 240V coil contactor internal, The Pro1 is a simple single stage controller, either for heating or cooling, not both. Nice digital control with a big display. I set it up for 44 deg, 1 deg higher than the garage temp without heat. I'll keep an eye on it over the next day or so and check the power consumption.

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PostPosted: January 19, 2019, 10:11 am 
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I thought that I would add to this with the following info.,

I have been running the heater, set at 44 deg, for several days now. I have a smart meter and can log into the electric co's website and see my usage. Here are some representable charts, The first chart was last week when I turned on the heat when I went our to work. There was a thermostat on the heater set for ~60 IIRC, normally the heater would turn off with temp down low at about 50 deg and continued to rise up to ~ 60 deg as the temps stabilized throughout the garage, This was before the installation of the new thermostat.
Attachment:
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the Monday is with no heat or work in the garage.
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no heat.JPG
no heat.JPG [ 36.86 KiB | Viewed 369 times ]


Wed and Thursday is with heat. All days were close to 44 deg in the garage. On the coldest Winter days I have seen temps going to ~26 deg in the garage. I chose 44 to see what the energy usage was costing me to maintain the temperature. However, the temps outside have been mild.

Attachment:
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Attachment:
heat.JPG
heat.JPG [ 38.94 KiB | Viewed 369 times ]


We are coming up to a week worth of normal Winter weather with temps in the single digits overnight. sub zero on next Saturday. I wonder how those will affect my electricity.

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