5kW shop htr- controlled by remote stat, best options?

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sw_ross

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Most 5kw shop heaters usually are controlled by stats integral to the unit, temp control, on-off, auto, fan, etc.

All the 10kw heaters I've install have an integral contactor that is controlled by low voltage t-stat mounted remotely.

I wish this option was available on the 5kw htrs.

I know there are htr relays that can perform this function, but the you get into ~$100 in mtl + labor.

I see a line voltage t-stat at the local box store that is rated for 28 amps and is being marketed for controlling shop htrs.

Question-

What is your preferred method of remotely controlling a 5kw heater?

I'm thinking about scenarios where the heater is mounted higher than the HO can conveniently access for controlling temperature.

Thanks!
 
purchase higher kW heater and disable some of the heat if you can't use all the heat for some reason? You don't spend extra on control transformer, relay, etc., don't need to spend the extra time or need space to mount them, and possibly come out about same cost but with something that looks nicer.

Finding a line voltage thermostat rated for the application is the other option. Worst case a replacement stat for the unit but remotely mounted I guess should work, or take the one out of the unit and remote mount it.
 
Good idea

Good idea

Good idea of installing a larger heater that has the built-in contactor and adjusting the wattege on the heater.

I'll have to do a cost comparison with the supply house to see what you get for your money.

Not sure about the 28 amp line voltage stats. Haven't installed one of those. It's a 2-pole stat with a positive off position. I'm wondering if the stat became satisfied and shut-off power to the unit, you wouldn't get the fan continuation (until the limit switch opened). Would that be hard on the heating elements for the heat to not disapate with fan blowing? Or is the fan continuation just to take advantage of leftover heat?
 
sw_ross said:
Good idea of installing a larger heater that has the built-in contactor and adjusting the wattege on the heater.

I'll have to do a cost comparison with the supply house to see what you get for your money.

Not sure about the 28 amp line voltage stats. Haven't installed one of those. It's a 2-pole stat with a positive off position. I'm wondering if the stat became satisfied and shut-off power to the unit, you wouldn't get the fan continuation (until the limit switch opened). Would that be hard on the heating elements for the heat to not disapate with fan blowing? Or is the fan continuation just to take advantage of leftover heat?
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I would think letting the fan continue to cool elements after opening heater circuit would lengthen life of those elements to some extent and is probably more of a benefit for that reason then any "leftover heat" advantages. Left over heat is still dissipated into the space unless it is a ducted system heating a different space then the heater location, but type of unit you are talking about is intended to be in the space it is heating.
 
kwired said:
I would think letting the fan continue to cool elements after opening heater circuit would lengthen life of those elements to some extent and is probably more of a benefit for that reason then any "leftover heat" advantages. Left over heat is still dissipated into the space unless it is a ducted system heating a different space then the heater location, but type of unit you are talking about is intended to be in the space it is heating.
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heat cycling the elements at higher rates actually decreases MTBF. i would just let them cool off in ambient w/o fan. the best way would be PWM control and to slowly turn on/off the heat.

shutting down your PC every night vs leaving it running will decrease MTBF, why? because of heat cycling.
 
Contactor

Contactor

Was thinking about a contactor setup... Previous employer used a 30 amp def purp contactor that had 24v coil. Then had a 240-24v xfmr for control circuit and a low volt t-stat. This was all mounted in a 6x6x4 box either by heater or by panel (not t-stat).

Could you you use an A/C contactor (like is mounted in condensing unit) to accomplish this same function? I know they make contactors with built in xfmr, single unit.

Any reason why it wouldn't be a good setup?
 
As in the home, it's more comfortable to have the fan constantly on, so the the air is moving past the thermostat and has a more accurate reading of the room air. That way, the temperature away from the thermostat actually fluctuates less.
 
FionaZuppa said:
heat cycling the elements at higher rates actually decreases MTBF. i would just let them cool off in ambient w/o fan. the best way would be PWM control and to slowly turn on/off the heat.

shutting down your PC every night vs leaving it running will decrease MTBF, why? because of heat cycling.
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Is it worth the cost for a relatively inexpensive heater in the first place? We are talking about a pretty basic electric unit heater of only 5-10 kW rating.
 
sw_ross said:
Not sure what these acronyms stand for?
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MTBF is apparently mean time between failures.

PWM is pulse width modulation - common description of how VFD's and inverter outputs work, great for varying speed of AC motors, and even great way to give fairly precise heating control for process operation, but probably overkill installation cost wise for controlling a basic space heater application.
 
kwired said:
MTBF is apparently mean time between failures.

PWM is pulse width modulation - common description of how VFD's and inverter outputs work, great for varying speed of AC motors, and even great way to give fairly precise heating control for process operation, but probably overkill installation cost wise for controlling a basic space heater application.
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I have been tempted to try a SSR on my garage heater just because I have one at the shop. Some day when I don’t have anything to do, it’s on my list.
 
The temperature of a room changes very slowly. Fast PWM control -- as is used in variable-frequency motor drives -- would put a lot of unnecessary transients onto the powerline.
A better option would be zero-crossing switching, with the minimum "pulse width" being a fairly large number of complete 60-Hz cycles.
 
triac using ~10-20Hz PWM

kwired said:
Is it worth the cost for a relatively inexpensive heater in the first place? We are talking about a pretty basic electric unit heater of only 5-10 kW rating.
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likely not.
 
Why do you need to mount the stat remotely? The stat that's built into the unit senses the return air and modulates it based on that temperature. The only time I would recommend using a remote stat is if the unit is mounted to a ceiling and is likely to get stratified air in the return.
 
rlundsrud said:
Why do you need to mount the stat remotely? The stat that's built into the unit senses the return air and modulates it based on that temperature. The only time I would recommend using a remote stat is if the unit is mounted to a ceiling and is likely to get stratified air in the return.
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He mentioned in OP that it is mounted high and wanted easier access to the thermostat for user.
 
What kwired said,

I've had a could of times where the height wasn't convenient for the HO to operate the controls. They got tired of using a broom handle to adjust the unit mounted t-stat!

Another situation I mounted the heater in the far back corner of a tight 2-car garage with the heater facing 45* across the space. It was about the only location available for mounting. But when the weather is cold and they have 2 cars jammed in it makes access to the heater a fight!
It would've been nice to install a stat near the man door into the house for convenient adjustment.
 
sw_ross said:
What kwired said,

I've had a could of times where the height wasn't convenient for the HO to operate the controls. They got tired of using a broom handle to adjust the unit mounted t-stat!

Another situation I mounted the heater in the far back corner of a tight 2-car garage with the heater facing 45* across the space. It was about the only location available for mounting. But when the weather is cold and they have 2 cars jammed in it makes access to the heater a fight!
It would've been nice to install a stat near the man door into the house for convenient adjustment.
Click to expand...


i not quite following. a stat is temp set. you would set the temp to say 70F for a garage that would normally get very cold, power on, then leave it alone.

but, maybe you can find some gadgets built around Alexa? set the unit stat to a higher #, say 80F for a max temp setting, but then control the up-to-max temp using Alexa, so you can just talk to Alexa from inside the house, "Alexa, heat garage to 72 degrees" and Alexa sends command to a temp sensing relay.
 
If you want to go a cheap as option as possible, a ladder to the heater is it. Cheapest electrical solution parts-wise, barring using the breaker as a switch and leaving the heater on/wide open, is a ~$25 line voltage thermostat mounted opposite wall in the shop and leaving the heater fan settings alone.

You may be able to replace the temperature control knob on the heater with a rotary pull-chain type, like what you might find on window sheers/blinds, to control it from the floor w/o a ladder or remote thermostat - do you have a picture/link to the heater you're using?
 
FionaZuppa said:
i not quite following. a stat is temp set. you would set the temp to say 70F for a garage that would normally get very cold, power on, then leave it alone.

but, maybe you can find some gadgets built around Alexa? set the unit stat to a higher #, say 80F for a max temp setting, but then control the up-to-max temp using Alexa, so you can just talk to Alexa from inside the house, "Alexa, heat garage to 72 degrees" and Alexa sends command to a temp sensing relay.
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If customer is a technology/gadget geek, then that sells.

If customer is thrifty, they will just get out ladder every time they want to change thermostat setting.

Many of such units around here they set fairly low just to keep above freezing and leave it there. Occasionally if they plan to spend some time in the garage they may want to temporarily turn it up some.
 
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