# Can I add a switch in line with the thermostat to a a garage heater?



## Sparcee (Sep 12, 2020)

I'm a commercial electrician wanting to add a 7500w 240v garage heater (w/ fan) to my garage for the winter. I want to mount it high up in a corner and face it towards the center but don't want to use a ladder to turn it on each time. The way I see it, I have 3 options for easier control: 

1) Per code, I'll be installing a service disconnect already. I _could_ use that as my switch. I don't like this option because it seems unsafe from arcing and disconnects aren't meant to be used as switches. 

2) Delete the built in Thermostat/switch and wire in an external one to the wall. 

3) Add a 120v switch in-line with the built in thermostat. I would keep the t-stat always on and control the on/off via the switch. 

The wiring diagram shows the t-stat is just a simple switch and is wired to L1, so 120v. I prefer option 2 or 3, and using the diagram, it should be an easy rewire.

What are you thoughts? Thanks!


----------



## Wirenuting (Sep 12, 2010)

You can use a two pole switch rated for the load. (Not best option)
Or interrupt the stat line before the stat.

Edit, interrupting the stat circuit is the best option. This way the fan will run for cool down and not just Kill the unit.,


----------



## Southeast Power (Jan 18, 2009)

I would install a thermostat within your reach.
1. It will be convenient
2. You will satisfy the temperature up to the level you actually feel. Near the ceiling will waste energy. Energy = hard earned $$


----------



## VELOCI3 (Aug 15, 2019)

Wire a 120V wall t-stat in parallel with the onboard t-stat. Set the onboard at max and use the wall t-stat to turn on and off. 


Sent from my iPad using Tapatalk


----------



## Navyguy (Mar 15, 2010)

Wirenuting said:


> You can use a two pole switch rated for the load. (Not best option)


Actually I think this is the best option. Not sure why you don't, willing to explain?

I think if he wants the fan to run, that that is a different situation then from what the OP asked, and I actually think the fan running option is a better idea.

Cheers
John


----------



## Sparcee (Sep 12, 2020)

I would love to add a toggle switch but they don't make two pole switches rated for this load (31a) that I'm aware of. Could I not add a single pole in line with the existing t-stat since it is only wired off L1, thus 120v?


----------



## Wirenuting (Sep 12, 2010)

Navyguy said:


> Actually I think this is the best option. Not sure why you don't, willing to explain?
> 
> I think if he wants the fan to run, that that is a different situation then from what the OP asked, and I actually think the fan running option is a better idea.
> 
> ...


The line diagram does not show it, but some of the little unit heaters I've installed in the past few years had the fan run for a cool down period after the Elements dropped out. 

A two poles with will also cause the High limit light to go out and he would loose his only warning that there is a problem. Who ever looks up at a unit just before you hit the off switch?


----------



## splatz (May 23, 2015)

You can find box mount type switches rated for 40a, for example 










https://www.automationdirect.com/ad...ntrollers_-z-_disconnects_(30-60_amps)/40002d 

That's going to cost you maybe $60 including a box and raised industrial switch cover. You could get a one arm bandit type disconnect in the same range, or if you shop for a cheap one a rotary type motor disconnect but most of those are more expensive. 

I agree with @Wirenuting where to wire a line voltage thermostat, put it between the supply terminal and the thermostat, in series, with the built-in turned high enough it stays on. It will probably weld shut soon enough anyway with the cheap ass environmentally friendly contacts they use. Of course so will the wall thermostat you add. So you'll be glad you have that switch. 

I just wouldn't use the switch to control the temperature. Only to shut power for the off season, and for the day when the thermostat eventually welds shut. 

I don't follow the OP part about the service disconnect.


----------



## Kevin (Feb 14, 2017)

VELOCI3 said:


> Wire a 120V wall t-stat in parallel with the onboard t-stat. Set the onboard at max and use the wall t-stat to turn on and off.
> 
> 
> Sent from my iPad using Tapatalk


In parallel with the onboard stat at max would mean the temp would have to get high enough for the onboard stat to open.

Either in parallel with the onboard stat, and turn the onboard stat all the way down

OR

Wire the onboard stat in series with the new stat, and turn the onboard stat all the way up.


----------



## VELOCI3 (Aug 15, 2019)

Kevin_Essiambre said:


> In parallel with the onboard stat at max would mean the temp would have to get high enough for the onboard stat to open.
> 
> Either in parallel with the onboard stat, and turn the onboard stat all the way down
> 
> ...



Parallel would allow either stat to energize the coil


Sent from my iPad using Tapatalk


----------



## Kevin (Feb 14, 2017)

VELOCI3 said:


> Parallel would allow either stat to energize the coil
> 
> 
> Sent from my iPad using Tapatalk


Yes, but you had stated to turn the onboard stat to max, which would mean heating the garage up pretty darn hot for the heater to shut off!


----------



## VELOCI3 (Aug 15, 2019)

Kevin_Essiambre said:


> Yes, but you had stated to turn the onboard stat to max, which would mean heating the garage up pretty darn hot for the heater to shut off!



Set it on whichever lowest or highest setting that will essentially bypass its capability in that environment. Safest way to do it would be disconnecting it completely and use the wall T-stat. 


Sent from my iPad using Tapatalk


----------



## sbrn33 (Mar 15, 2007)

Wirenuting said:


> You can use a two pole switch rated for the load. (Not best option)
> Or interrupt the stat line before the stat.
> 
> Edit, interrupting the stat circuit is the best option. This way the fan will run for cool down and not just Kill the unit.,


That stat line is the best option. Shutting the whole thing down hot will shorten the life on the elements.


----------



## emtnut (Mar 1, 2015)

I would go with a contactor, in parallel with the onboard tstat.

24vac coil leaves a lot of t-stat choices.
I don't think you'll find a 40A t-stat easily, and will be pricey if you do.
The heavy duty switches are pricey too.






The block diagram shows fan control wiring direct to 240V, so this unit probably runs the fan after thermostat opens (as Wirenutting said)


----------



## Wirenuting (Sep 12, 2010)

sbrn33 said:


> That stat line is the best option. Shutting the whole thing down hot will shorten the life on the elements.


It sounds like he wants it for his own garage. 
It makes me think he doesn't plan to heat the garage all winter, just warm it up as needed for working in it. 
As such I would only break the stat circuit with a wall switch. Let the onboard thermostat control the temp.. 
The garage might be uninsulated and if a stat in lower on the wall,the thing would never shut off.,


----------



## Dennis Alwon (May 9, 2009)

Do you really mean 7500 watts. As stated earlier that is 31 amps but then you need to multiply by 1.25 =38.75 amps. You need a 40 amp circuit.

What size conductor are going to the garage?


----------



## Navyguy (Mar 15, 2010)

Wirenuting said:


> The line diagram does not show it, but some of the little unit heaters I've installed in the past few years had the fan run for a cool down period after the Elements dropped out.
> 
> A two poles with will also cause the High limit light to go out and he would loose his only warning that there is a problem. Who ever looks up at a unit just before you hit the off switch?


I get that and I am not sure if the fan "cool down" for an electric element is necessary, but not my area of expertise and I did not consider it; although I thought having the ability to run the "FAN" might be a good option just to circulate the hot air near the ceiling.

If there is a "problem" with the heater, disconnecting all the power going to it is better then only one phase in my estimation; but again that eliminates the "FAN" option.

Cheers
John


----------



## Wirenuting (Sep 12, 2010)

Navyguy said:


> I get that and I am not sure if the fan "cool down" for an electric element is necessary, but not my area of expertise and I did not consider it; although I thought having the ability to run the "FAN" might be a good option just to circulate the hot air near the ceiling.
> 
> If there is a "problem" with the heater, disconnecting all the power going to it is better then only one phase in my estimation; but again that eliminates the "FAN" option.
> 
> ...


Ok, I understand what your saying. It's been only a few that I've installed that had that cool down period for the coils. Those units seem to last longer. Running just the fan is a good idea also. If it was my unit at home I would wire in that option. 

But disconnecting all phases to the unit will kill the over temp alarm light. 
At work we might look up at a unit before we disconnect it, but at home we are all inherently lazy and just hit the switch as we walk out.


----------



## VELOCI3 (Aug 15, 2019)

emtnut said:


> I would go with a contactor, in parallel with the onboard tstat.
> 
> 24vac coil leaves a lot of t-stat choices.
> I don't think you'll find a 40A t-stat easily, and will be pricey if you do.
> ...



The shown t-stat will only have the coil load on it. Not the heater 


Sent from my iPhone using Tapatalk


----------



## emtnut (Mar 1, 2015)

VELOCI3 said:


> The shown t-stat will only have the coil load on it. Not the heater
> 
> 
> Sent from my iPhone using Tapatalk


Thanks, I overlooked that !


----------



## bill39 (Sep 4, 2009)

Since a thermostat is just a fancy switch installing a normal single pole switch in its place would work.

Now the downside: let us know how high your bill is after forgetting to turn the switch off and leaving for the day. You’ll be lucky if it doesn’t burn it down from running constantly.


----------



## Quickservice (Apr 23, 2020)

Sparcee said:


> I'm a commercial electrician wanting to add a 7500w 240v garage heater (w/ fan) to my garage for the winter. I want to mount it high up in a corner and face it towards the center but don't want to use a ladder to turn it on each time. The way I see it, I have 3 options for easier control:
> 
> 1) Per code, I'll be installing a service disconnect already. I _could_ use that as my switch. I don't like this option because it seems unsafe from arcing and disconnects aren't meant to be used as switches.
> 
> ...


I installed the same heater last winter. I simply installed a 20A 2PST 1-hour spring timer switch. Works great.


----------



## RRF (Nov 5, 2016)

IMO option 3 is the way to go. However keep in mind that your new toggle switch, even though lightly loaded, will see 240 volts. Not 120 volts.


----------



## VELOCI3 (Aug 15, 2019)

RRF said:


> IMO option 3 is the way to go. However keep in mind that your new toggle switch, even though lightly loaded, will see 240 volts. Not 120 volts.



The T-stat only closes L1


Sent from my iPad using Tapatalk


----------



## RRF (Nov 5, 2016)

It's implied that it is a 240 volt circuit.


----------

