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Digital programmable thermostat for 240V inductive load electric wall heater?

Digital programmable thermostat for 240V inductive load electric wall heater?

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  #1  
Old 11-20-05, 02:11 AM
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Digital programmable thermostat for 240V inductive load electric wall heater?

I'm managing and upgrading a 9 unit apartment building, built in 1960, in San Diego near the beach. I just replaced a room dominating gas wall furnace in a 350 ft2 studio with a 240V electric fan forced wall heater (Qmark GFR2402, 2400W at 240V, finned tube heating element), to free up space for a bed. I want to control it with a programmable digital thermostat, largely for the high tech look rather than for the programmability....programmability is a little overkill for a studio. The heater design specifies a single pole or double pole thermostat just switching 240V on/off. Additionally, it has the heating element and fan motor in parallel, making it considered an inductive load due to the fan motor.

The only digital programmable thermostats I've found are the Honeywell TL8230A1003 at Grainger.com - has a great high tech look and reasonable at $60, but does not handle inductive loads. It's intended to control electric baseboard heaters, which have no fan motors. The other is from Qmark but looks to have the same LCD as the Honeywell...they're probably the same electronics. Qmark's website lists the DSB2402 digital thermostat as handling inductive loads, but a call to tech support revealed they no longer make it.

I'm thinking: the main additional demand on the thermostat from switching an inductive load is for greater current handling capability in the relay switching the load. I'm considering
1) just buying this Honeywell, taking it apart and replacing the relay with one with higher current handling, suitable for whatever initial current surge the fan motor in the heater takes. I've done some electronic system design so this might be as easy as a search on the DigiKey website for a suitable relay
2) Just try it as is, on this Qmark heater....I wouldn't think the fan motor inrush current would be that much...it's a little 4"" cylindrical ""tangential blower"" fan, not some honking 48"" warehouse fan.

The alternative is to use the mechanical non programmable uncalibrated "HI/MEDIUM/LOW" thermostat in the unit. Not just low tech looking but could confuse tenants.

Any thoughts?

Links:

Qmark electric heater
http://www.qmarkmeh.com/

Honeywell thermostat at Grainger
http://www.grainger.com/Grainger/wwg...556766&ccitem=

Honeywell's nearly information-free website:
http://yourhome.honeywell.com/Consum...ge/Default.htm
 

Last edited by StainlessSteel; 11-20-05 at 02:15 AM. Reason: typos
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  #2  
Old 11-21-05, 02:00 PM
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I'd see if you can get a heater relay box, and use a 24V timed thermostat.
 
  #3  
Old 11-24-05, 12:24 PM
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I'd try using the thermostat to control a seperate relay that can handle the current load. It's a pretty standard way to split high current loads from low current control circuits.
 
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Old 11-24-05, 03:50 PM
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Thanks for the replies. Anyone know where to get information on such relays? In particular, are they small enough to fit in a single outlet electrical box with the digital thermostat? If not that means a lot more complexity than i'd bother with.

A separate relay would at least allow me greater digital thermostat selection by allowing use of a Home Depot style low voltage thermostat

Even better though would be finding a relay that's a plug-in/solder-in replacement to the non-inductive-load-only relay on that Honeywell 240V digital thermostat. This would eliminate having to make a separate box and extra connections....
 
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Old 11-24-05, 05:14 PM
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Try this one: the System Sensor PR-1. The link will take you to the spec. sheet. The coil operates on multiple voltages, and the contacts will handle 10amps at 230v. The trickiest part is finding someone who sells it.
 
  #6  
Old 02-11-06, 01:57 AM
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Digital thermostat really is OK! All is good

So, in early January 2006 I ended up talking to a different tech at Qmark, who said the Honeywell LineVoltPro8000 digital programmable thermostat should work just fine with the GFR series fan-forced electric wall heater. I had worried about things like power factor correction, but according to this tech, the fan motor in the Qmark heater was approx 0.1 horsepower or less, so inductive loading or power factor effects were insignificant...as i kinda suspected anyway. I tried it out...it works great. It definitely puts out less heat than the gas wall furnace, but in San Diego's mild beach climate that's not a problem...tenant has had it for 4 weeks now (January) and is happy. I did think it best though, to jumper down the Qmark output to 1800W from 2400W, as the grille and immediate surrounding drywall got worrisomely hot to touch.

I also underestimated how great the LineVoltPro would look: absolutely drips with quality feel, and high tech yet interior decorator quality styling. Looks like it costs 5x the $59 at Grainger; also at air-n-water.com for like $79.99...

It's tragic though, how difficult it was to track down whether this would work. Due to Honeywell's insufferable dumbed-down vague thermostat website, and inaccurate tech support from both Honeywell and Qmark, I was told they were incompatible. Most people would then just settle for the crappy built in thermostat in the Qmark, missing out on the beautiful elegant design and function of the Honeywell LineVoltPro, Qmark and Honeywell have reduced sales and customer satisfaction, property managers and tenants have lower standard of living....

And i take back "programmability is...overkill for a studio"....programmable thermostats can serve as a nice "alarm clock" - it's easier to drag yourself outta bed to a warm room.

I now totally recommend this combination for those upgrading/condo converting 1940-1980 vintage studios and small rooms, in a mild beach climate who want to replace a space wasting, overkill, carbon monoxide and gas leak risking gas wall furnace...this frees up space, gives a designer look, and adds high tech looks and programmability for about $250 in parts. Labor to open up drywall to run wiring and add a 220V capable subpanel was significant though, about 1 day handyman $200/day plus an electrician buddy to install the subpanel for $125....but if you're already painting, that's 'free"...
 

Last edited by StainlessSteel; 02-11-06 at 02:46 AM.
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