Multiple Cadet Hot One electric heaters on Ecobee thermostats

slodat · Jan 16, 2018

I have (2) 5/3.3kw, 17060/11372 BTU and (4) 4/2.67kw, 13648/9100 BTU Cadet Hot One electric heaters in my 3500 sq ft shop. In general I only use 4-5 of these heaters. This means making a lap around the shop to turn the heat up on arrival to get the place habitable, another lap to turn down to maintain temperature and another lap prior to leaving for the day to lower the heat to a lower, minimal level. We don't have natural gas here, so I'm stuck with electric heat/heat pumps. I also have (2) Pioneer 24,000 BTU mini-split heat pumps. The heat pumps don't heat below about 40F. They are a couple years old now and work great to cool the shop. They do a good job of keeping things comfy in the spring and fall, but I'm on the resistive heat in the winter months.

The multiple laps around the shop every day are enough to make me want a thermostat. AND, I'm certain the winter electric bills have a lot of room for improvement. So, I've decided to convert to a modern, smart thermostat. I ordered the Ecobee3 lite. It will interface with my existing electric heaters via Aube RC840T-240 On/Off Switching Electric Heating Relay with Built-in 24 V Transformer . One relay per heater. I will have two thermostats with two remote temperature sensors each.

Parts are on the way. Installation looks straight forward. More to follow.

Bill of materials:

Enclosure - I will be housing these components in an enclosure near my main electrical panel.
24v 40VA transformer - this powers the thermostats and the control loop for the relays.
Thermostat for each "zone" of heat. In my case two. Ecobee3 lite (you can use other thermostats, this is what I chose because of the remote temperature sensor capability)
Relay for each heater. I used Aube RC840T, but then opted for an external transformer. So, the Aube RC840 would be a less expensive part ($40 vs $29 each from Supply House)

I welcome any input or advice.

u3b3rg33k · Jan 16, 2018

There's probably something wrong with your heat pumps - the manual states heat operation from -15°C - 30°C.

It might be worth moving to traditional split style heat pumps if you're having issues with minisplits. The previous place I worked had some installed by a less than competent contractor and they always had issues. they'd work for a year or two after he evac'd and re-charged them.

slodat · Jan 16, 2018

I don't think there is anything wrong with the heat pumps. They are pretty low end and when I talked to Parker Davis (the supplier) they said they don't heat much below freezing. The outdoor unit coil freezes up pretty fast and then the defrost cycle takes a while. In the end, I turn them off when temps hit freezing. Both were installed by a competent HVAC technician.

sleek98 · Jan 16, 2018

Would love to see how it turns out. I would like to do the same as well.

slodat · Jan 16, 2018

sleek98 said:
Would love to see how it turns out. I would like to do the same as well.

I'm feeling pretty good about this on paper. All of the heaters are on home runs to the panel, so I'm going to install the control relays in a box near the panel. That part of the wiring will be straight forward. Then the 24v stuff will be wired in parallel for each thermostat. Should have this going in a few days..

slodat · Jan 16, 2018

Got one of the relays today from Amazon. The rest are coming from Supply House ($20 less each).

Stuff · Jan 16, 2018

There have been some reports that the RC840T does not have enough capacity to power the Ecobee while others have been fine. The Aube shows that it supplies 1.2 VA while the Ecobee spec calls for 3.5 VA.

Wiring note: Attaching more than one Aube to a single thermostat is unusual and has some issues. Hooking multiple Rs together puts the Aubes' transformers in parallel which causes a dead short if out of phase. So for the first Aube use R,W,C to the thermostat but the others only hook up W and C. Then measure from R to R to verify zero volts and not 48+. For multiple relays it is much easier to use a separate higher powered transformer.

slodat · Jan 16, 2018

I understand the issue if parallel transformer primaries are not all connected to the same leg, no problem there. I have read that using multiple RC840T's works well. I'm going to give it a try.

sleek98 · Jan 16, 2018

I have not used a 240v relay before so sorry if this is basic. (EDIT found a color diagram and made a couple changes to the way I thought it would be wired)

Wiring from the breaker to the heater currently is L1 Black, L2 white (taped to show hot) and ground. Assuming putting the relay in the heater.

Black wire would go from the breaker to the L1 heater, The blue from the relay would also go to the L1 on the heater (thus it has 2 wires going to it), or in a wire nut have 3 lines, short jumper wire the L1, blue to the relay, and black from the breaker.

White wire from the breaker would be connected to the black on the relay and end there. Then the red from the relay would be connected directly to the L2 on the heater?

Do you only have to break one leg of the 240 to turn the whole thing off? Wonder if the fan will stay running with one side still hot. I have only used relays in the auto side so this is new to me.

Then to tie in the next relay you run C to C then W to W and you no longer hook up the R to R? IF your not using the R on the rest of them can you swap it out for a RC840? Looks like they are 10 bucks cheaper per. and then you dont have to mess with taping the blue wire.

slodat · Jan 16, 2018

I went ahead and ordered a 40VA transformer.

sleek - you are understanding correctly. I wish I would have seen the RC840, would have saved me some cash. I will not be using the internal transformer, it doesn't have enough VA to run both thermostats.

u3b3rg33k · Jan 16, 2018

I went and built something similar. I wired up a contactor so i could have a real thermostat control a window AC. The contactor is probably overkill (way bigger than the relay they use for the compressor), but the only downside is the authoritative clunk it makes when it engages.

Here's the working prototype (OSHA approved)

slodat · Jan 16, 2018

slodat · Jan 17, 2018

I went ahead and purchased a 40VA 24vac transformer after reading the ecobee3 can need up to 3.5VA. The transformer will eliminate that concern and it was only $12.

Thermostat, remote sensors and one RC840T arrived. So I have one 5kw heater up and running on the thermostat. It’s all working. I’ll get the control enclosure together when the rest of the parts arrive.

The short version is this is going to work. Well. Like really well. I’m undecided if I want to set up two zones. With a “zone” being a thermostat controlling a group of heaters. I’m going to start with one thermostat and use the hi/low switches on the individual heaters to try to get a balance.

Bench test rig running one relay/thermostat:

Stuff · Jan 18, 2018

Good to see that your proof of concept is working!

sleek98 · Jan 18, 2018

Nice.

slodat · Jan 18, 2018

Maybe someone who knows more about HVAC stuff has thoughts on my layout.

My shop:

Bays 1-4 are around 550sq ft each. Bay 5+6 is 1200 sq ft. There's not a huge temperature difference through the shop in general. The exception is when the sun is hitting the Bay 1 mini-split heat pump's outdoor unit.

The Ecobee3's remote sensors can be selected/deselected for use in the base temperature calculation. So, if it's warmer is Bay 1-3 because the heat pump is effective, I can exclude it from the thermostat's room temperature so this warmer area doesn't affect the thermostat calling for more heat in Bay 5-6. This is the third winter I've had the Cadet heaters and mini-splits. The mini-split in Bay 5/6 stops working well once it turns really cold (<32F). The Bay 1/2 unit seems to keep working in general. When temps drop to single digits, it isn't effective either. I'm thinking my initial strategy will be to have one thermostat control all heaters. I can use the Hi/Low switches on the heaters to try to balance things out.

Edit: I used loadcalc.net to get an idea of heat load using 5F outdoor and 65F indoor. I don't see temps <20F much and I keep it a closer to 63F inside. Looks like 25kBTU for Bay 5/6 and 38k for Bay 1-4 for these worst case numbers.

Heater locations:

Bay 1- 5kw Low 11kBTU
Bay 2- 4kw Low 9kBTU
Bay 3- 4kw Low 9kBTU
Bay 5/6 5kw(Hi 17kBTU) and 4kw (Low 9kBTU)

u3b3rg33k · Jan 18, 2018

with 18kW of electric heat ($$$$), I'd get a standard sized 3 ton (not mini) split, 2 stage (gives you roughly 2 ton low, 3 ton high) heat pump - simple, and do work down to cold temps (0F). then your ecobee can use W1/W2 and a relay to kick on the electrics to fill the difference. ROI should be pretty good if you're keeping it heated.

slodat · Jan 18, 2018

You are right on the ROI. I have some of the lowest electric rates in the country $0.04/kWh. That’s about $0.88/hr of run time. Pioneer has a very nice looking variable speed conventional split system for about $3k that I’m thinking would be a good fit. It’s not in the time or money budget at this time. And, I want the resistive heat as a backup anyway. So, I’ll sort this and shoot for the big split when time and cash flow allow. I have away temp set at 46F. I can’t risk freezing my laser tube..

u3b3rg33k · Jan 18, 2018

I need more details on the laser asap.

slodat · Jan 18, 2018

u3b3rg33k said:
I need more details on the laser asap.

Lots of info in my shop thread. Boss 150 watt LS3655 CO2.

slodat · Jan 19, 2018

As these type of projects go, I've continued to read and research. I am very happy with the Ecobee3 lite. I have four of the remote temperature sensors throughout the shop and I'm using the two in Bay 5/6 to control the thermostat. The ecobee3 is working great with the RC840T controlling the one 5kw heater. Should be able to get the components wired in tonight for all five heaters.

u3b3rg33k · Jan 19, 2018

I'm not familiar with the ecobee, but one of the things I like about my honeywell is the ability to control staging - it defaults to 0.5ºF in comfort mode, but you can tweak it up to 3 or 4ºF between stages. then if you turn on the backup heat option, you can lock out based on outdoor temp, and/or set it up to 15F below setpoint.

this is useful if your heaters are too big for the space, or if you have something like a heatpump and want to minimize operation of the aux (electric) to save money.

Jbullfrog · Jan 19, 2018

The Cadets need to have the fan run longer then the element. This is why they specify not using 240v thermostats with them. The fan runs to cool the element down gradually so it doesn't heat stress.

slodat · Jan 21, 2018

Mine don’t run the fan to cool the element after the thermostat drops out. I suppose if I burn up an element I’ll look at this. Installing now.

slodat · Jan 21, 2018

Enclosure ready to be mounted and wired in.

For now, the thermostat will be mounted to the enclosure door. The remote sensors mean you can mount the thermostat anywhere..

The holes in the enclosure were there when I bought them- Ebay surplus special. Saved a good bit of cash. I’ll make a cover at some point.

u3b3rg33k · Jan 22, 2018

slodat said:
Mine don’t run the fan to cool the element after the thermostat drops out. I suppose if I burn up an element I’ll look at this. Installing now.

Venturing a guess, but if you aren't cycling at a crazy rate and causing the elements to heat up but the fans to not move air over them, the elements should be OK. surface temp may rise briefly, but the core temp should not - does my thinking make sense?

It's my understanding most smart thermostats have a timer to prevent short cycling equipment.

slodat · Jan 22, 2018

I’m set at 5 minutes minimum. I was in the shop 12 hours yesterday. No excessive cycling. All in all this is turning out really nice. I have three of the five heaters transitioned to the thermostat. My away temperature is 45F, and it’s not dropping below 50F since I installed it. Outside temps aren’t dropping below freezing. This will really shine when it’s colder.

I like that the shop is up to comfortable temperature when I arrive. A lot.

slodat · Jan 25, 2018

Ok. This is working really well. Ecobee3 lite is controlling (2) 5kw and (3) 4kw heaters via the RC840 relays. All powered up via a 40VA 24v transformer. Very happy with the control this gives. Shop is warm when I arrive and heat isn’t running at all when I’m away (this is in part because of our mild temperatures since installation).

slodat · Mar 27, 2018

Been using this system for two solid months. Beyond happy with it! My electric bill is down significantly from last year for the same months.

drivesitfar · Jan 6, 2021

SD: thanks for leading me to your thread. since I only have a small 2 car garage that is packed with stuff and it will be insulated i'm probably good with one 5,000 Cadet "the hot one".

so did you buy yours new at Home Depot or where cause if i recall correctly you might have found one on Craigslist?

when you were just running one or two was it heating up a small area ok? any issues to mention with these heaters cause the reviews are not all great?

good to see you have yours all wired up and i bet your rates next to that huge dam are a lot better than mine here on the wet side of the state.

cheers

slodat · Jan 6, 2021

Well shoot.. Looks like Cadet no longer makes these heaters. I never found anything comparable. Most of this style are very loud with high speed fans. Hmm.

drivesitfar · Jan 6, 2021

SD: that's what i was thinking and I rarely find one used to buy. if you are having good luck with yours i'll maybe see if buying a used 5k for $100 might work ok for me cause i've seen them for more or less at times.

thanks

u3b3rg33k · Jan 10, 2021

slodat said:
Well shoot.. Looks like Cadet no longer makes these heaters. I never found anything comparable. Most of this style are very loud with high speed fans. Hmm.

I've got a $100 NIB electric 5kW heater with a pretty quiet (i.e. not high RPM) fan in it.

still available at the same price:
https://www.northerntool.com/shop/tools/product_200578579_200578579

been a bit but I'm pretty sure the manual says you can wire in a contactor. by default it's snap-disc controlled, both for fan start (no cold blast) and overheat shutdown. I've been too lazy and just leave it set at about 11:55 for 45F ish, and 2:00 ish for 65F ish.

drivesitfar · Jan 27, 2021

I was wondering if you've ever taken apart and cleaned or did any repairs to your Cadet Hot ones?

I just picked up about a 10 year old one that I was told worked great, but it's filthy so thinking I should give it a good cleaning before I find a spot to hang it in my small 2 car garage. I picked up the 220 plug to wire in at HD last night on my way home from picking up the heater that is not a standard dryer plug, but was next to them in the store.

when you were on manual mode was there a setting for a smallish 10x15 area you used and how long did you run it at full speed before turning it down or maybe there is a temp setting that controls that?

thanks for your help!!

drivesitfar · Jan 30, 2021

the seller thought his old cadet heater hot one worked so I handed him $50 to give it a try. I was going to clean it up a bit cause looked like it had been in a wood shop before I plugged it in. I wired up a new 220v 20amp receptacle for it and plugged it in and got heat and only a hum instead of the fan moving.

the seller was happy to give a refund and he said i could keep the heater so my question is it it worth it to replace the fan motor for $75 plus shipping or am I throwing good money after bad? and it looks like plug and play to replace the new motor, but is it?

at least I finished wiring a 220 plug that I had run the 10/2 wire for almost 30 years ago (decided against baseboard heater in this location, but never removed the wire.

any thoughts?

slodat · Jan 30, 2021

Turn the fan to ON and see if the fan turns on. In Auto it doesn’t turn the fan on until the elements heat up.

drivesitfar · Jan 30, 2021

It didn’t work on either setting but good to know. Thank you

It just Hums ir a steady buzz which I’m pretty sure isn’t a good thing

slodat · Jan 30, 2021

Try spinning the fan by hand in the on position. Most likely the motor needs some oil on the shaft.

drivesitfar · Jan 30, 2021

Good to know the fan only works on one setting. Thank you

Unfortunately I tried all the settings before telling the seller it wasn’t working. The loud humm or buzz is kinda a giveaway that something is stuck or burned out. I might take fan motor apart before I order a new one

drivesitfar · Feb 11, 2021

while i was researching where to buy a new fan motor to maybe fix the Cadet Hot one 4000w heater I found a seller selling 2 almost new ones. SO I drove 90 minutes and brought the 4000w & 5000w home.

I plugged the 4000 watt one in and it works great. i'll wire up for the 5000w and it should work too cause it looks newer. my garage is only a 2 car so I won't need to run both heaters at the same time, but I'll be able to heat one side more than the other when i'm out there working in one.

Multiple Cadet Hot One electric heaters on Ecobee thermostats

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