setback thermostats and Harman Pellet stoves

[HarryBack]

Ive noticed a few questions awhile ago about setback thermostats and pellet units. Harman just came out with a Technical Bulletin concerning them, and I thought Id take this time to communicate it before I forget all the particulars.

All Harman pellet units can utilize a setback thermostat. The thermostat must be:

1. Millivolt compatible
2. Have gold contacts
3. be low voltage
4. be low current


Harman reccommends the following Honeywell units for this use:

RTH230B
RTH6300B


If there is a jumper between Rh and Rc, it must be removed from the terminal block of the thermostat. The thermostat must be connected in series with the room sensing probe using the Rh and W terminals of the thermostat. Except with the P38, which has no room sensing probe, the set-back thermostat MUST be used in conjunction with the room sensing probe.

there are two modes of operation as well:

Occupied Mode: (someones home)
Set the thermostat to its max temp setting. The stove room-sensing probe will control room temperature, so set the desired room temp on the stoves temp dial.

Unoccupied Mode: (noones home)
Program the thermostat to the desired set-back temp. When the thermostat opens (is satisfied) the stove will go into a 4-blink status. If the stove is a auto-ignite model and the auto/manual switch is in auto, the stove will shut down. When the thermostat closes (calls for heat) the 4-blink status will reset and the stove will ignite.
If the stove is a manual ignition model, or an auto-igniting unit with the selector switch set to manual, the stove will go into the 4-blink status when the thermostat opens (is satisfied) and the stove will go to a minimum burn and stay there until the thermostat closes (calls for heat). When the thermostat closes, the 4 blink status will reset automatically.

Consult your owners' manual for a description of the 4-blink status. This error occurs when the contril board senses the room sensing probe isnt connected or has failed. This happens with the thermostat in series, since when the thermostat opens (is satisfied), there is a loss of continuity in the room-sensing circuit. The 4 blink status automatically resets when the board recognizes the room-sensing probe has been reconnected (ie: when the thermostat closes and calls for heat).


Anyhow, here's the gist of the tech bulletin. If it sheds some light, great.

 

[allenfrme]

It's always interesting to see how others use their stoves ! My 68 is just set to comfortable room temp most of the Winter, about 68, and left there. In the Fall and Spring, when it gets warm, it shuts off, and comes back on when the house cools. I just sorta forget about it except for the weekly 15 minute cleaning routine!

I tried shutting it down, or lower in the evening, but found I was burning more pellets getting the house back up to temp. Plus, it's not like a furnace, where you have heat a couple minutes later, as we all know, it takes a few to get going again !

My only, only , real complaint about Harmon is the lack of communication from the company itself. And I dearly wish they would find someone to design a better loop control for the thermostat ! The difference between 65 and 70 is a minor twitch of the fingers on mine !

Anyone heard about the new burn pot upgrade for the 68 ?

 

[Hammerjoe]

Sorry for bringing this old topic back to life.

Is anyone here using this setup?
How good does it work?

Any other compatible models besides those two honeywells?

The idea for me to use a t/stat is mainly to use it during fall/spring season and not so much in the winter due to the cold temps.
During fall and spring, temps are not that low that having the stove off when we are at work and have it turn on like half hour before we get home it shouldnt take too long to heat the home.
Any opinions on this?

Btw it would be really cool if someone that has a Harman with t/stat would post some pictures on how the wiring is done on the t/stat.
Thanks.

 

[mkmh]

I did this last night with a Honeywell RTH230B Thermostat. Sorry...no time for a pic right now as I have to head off to work. It took me about 5 minutes to set it up. Very simple just like the bulletin. I did have to remove the jumper from the thermostat as stated in the article.
My plan is to just use the thermostat for turning the stove on at 5 AM and off at 8 or 9 PM...then maybe one cycle mid-day. So far it shut the stove down for me and started it up for me this AM with no trouble.

 

[Hammerjoe]

Thanks for the reply.

How did you program the t/stat?

I am concerned about the electronics of the stove by using a t/stat.
Will it warm in any way the stove if the t/stat opens and closes alot, ie suppose the stove is set up for a temp of 70f and we the t/stat is programmed for 65f.
The T/stat will close and the stove will start working trying to reach the 70f temp, but as soon it goes over 65 the t/stat opens and the stoves starts shutting dow, but as soon it goes lower 65F then it is told to start again and so on and this I would think very frequently.
Will this constant open and close not cause any problems to the stove??
I cant imagine it not doing any harm!

 

[Tristan]

Very exciting topic. This is exactly what I am looking to do for my Harman XXV. I totally agree with HammerJoe on the spring/fall thing. I would like to be able to have my stove fire up to 75 deg at 5am to warm up the living spaces and the bathrooms down the hall (nothing like having to pee in the cold) and then having the stove settle down to about 65 during the day when no one is home, etc. This t/stat discussion is exactly what i am looking for. Can those with expertise and experience in this matter please chime in so that we may learn from your vast knowledge. Pictures ... pictures of the wiring etc would really help. Thank you.

 

[Tristan]

I just found the wiring diagram for the set back thermostat. Interestingly, I currently have the exact honeywell t/stat that is recommended by Harman, its currently controlling my (now defunct) oil guzzling baseboards ..... hmmmm....


http://oatstoves.com/files/pellet_stove_tsta_tinfo.pdf

Follow the link above.

 

[mkmh]

I think your concerns are valid. These stoves are not meant to be run with a programmable thermostat, and the Tech Bulletin basically provides a way to trick the stove into "thinking" one of the leads to the room sensor probe has lost its connection...which causes the stove to go into shutdown mode. When the thermostat calls for heat again it completes the circuit and the stove picks up on the fact that the room sesning probe is in place again...causing a start-up cycle.
If you are looking for precision heating i'm not sure i'd recommend this arrangement. As people have mentioned, it could lead to many shutdowns and start-ups, which is ineffiecient...wastes electricity, taxes the igniter, and may "mess with" the electronices of the stove.
What i've done is programmed teh thermostat to ensure that it only triggers one to 2 cycles per day.
Basically it starts up at 5 AM and will run until 9 AM or 90 degrees (which will never happen). At 9 AM until 4 PM it cycles down to 50 degrees (which ensures it will go into shutdown mode and stay off until 5 PM). At 5 PM it calls for heat again (90 degrees) until 8 PM....then from 8 PM - 5 AM it is back to 50 degrees ensuring that it stays off.
Probably still not fantastic for the electronics, but it IS a Harman bulletin, so this method is not entirely unsupported.

I'm doing something very similar with my Hastings St Croix, with good results. Basically you just have to keep in mind that your stove is not realy meant to be run the same way you'd run a forced hot water furnace. However, the auto on/auto off seems to be pretty low risk to me, and adds a huge measure of convenience. I'll post pics if I get a few minutes tonight, but the configuration is really very simple (just like in the bulletin).
Hoppe this helps

 

[mkmh]

One other note. My stove settings are as follows.
---------------------------------
Room Temp Mode (Automatic) toward the middle of the dial
Temp setting around 85 degrees
Feed Rate 1
-----------------------------
This morning I found that the basement was getting too warm so I went in and turned the dial to the off position. Even though the thermostat was calling for heat, this initiated the shutdown as expected. I figure I will be doing a fair amount of this tweaking to the stove settings to get a comfortable temperature. For example, when it start to get a little colder I will most definitely kick up the feed rate to 2 or 3.

Again, I am not expecting to achieve perfect stability in temperature...but the convenience of the auto starts and auto shutdowns is BIG for me. So far I am really liking my P61A. I've probably run through about 4 days of pellets and there is nearly zero ash build-up...and zero clinkers (NE hardwoods). I can tell that it is going to be a very low maintenece stove.

 

[Tristan]

When you say that there is nearly zero ash build up - where exactly is this ash build up expected to be? Indeed my XXV has little ash build up also, but nonetheless there is ash at the tip of the burn pot (approx 1" wide from the tip extending back towards the fire itself) ... is that normal ash? Or is that excessive?

Back to the original topic .... I am really excited about the potential of the t/stat automation. The wiring diagram shows a Rh and a W terminal to be connected to the Honeywell t-stat, this then gets connected in a series to the room sensor ... my question is ... do i make this connection to the room sensor's red wire? (which room sensor's wire gets the series connection?) Thank you.

Also, is there a way to extend the original room sensor?

Thank you again.

 

[Amaralluis]

One other note. My stove settings are as follows.
---------------------------------
Room Temp Mode (Automatic) toward the middle of the dial
Temp setting around 85 degrees
Feed Rate 1
-----------------------------

Feed rate of 1?? is that for the Harman?? That is strange, the advice on this board is to actually have it higher than four.
I have kept my accentra at a 4 but after reading a few topics here I decided to change to a 5.

To put it simply the t/stat can only be used as an on/off mechanism for the stove and not a temp controller.
And that is exactly what I need.

 

[mkmh]

Based on my limited expereince, I think your summary is about right Amaralluis.
Yeah, feed rate of 1 seems to work well for me. 2 when I want the flame a little higher. The one time I had it as high as 5 I was getting a really high flame out of it....it was overkill for my 700 square foot basement. I imagine as the temp continues to drop i'll have the feedrate back up in the neighborhood of 3...but I don't think i'll ever need to go higher than that.

I have not taken any precise measurements, but it seems like feedrate of 2, dist blower on high, temp set in the 85ish range my stove goes through about 1.25 pounds of pellets per hour.

My guess is that a feedrate of 5 would get me up there in the 50-60,000 BTU range.....which would definitely make the basement a bit too toasty

 

[Hammerjoe]

I think your concerns are valid. These stoves are not meant to be run with a programmable thermostat, and the Tech Bulletin basically provides a way to trick the stove into "thinking" one of the leads to the room sensor probe has lost its connection...which causes the stove to go into shutdown mode. When the thermostat calls for heat again it completes the circuit and the stove picks up on the fact that the room sesning probe is in place again...causing a start-up cycle.
If you are looking for precision heating i'm not sure i'd recommend this arrangement. As people have mentioned, it could lead to many shutdowns and start-ups, which is ineffiecient...wastes electricity, taxes the igniter, and may "mess with" the electronices of the stove.
What i've done is programmed teh thermostat to ensure that it only triggers one to 2 cycles per day.
Basically it starts up at 5 AM and will run until 9 AM or 90 degrees (which will never happen). At 9 AM until 4 PM it cycles down to 50 degrees (which ensures it will go into shutdown mode and stay off until 5 PM). At 5 PM it calls for heat again (90 degrees) until 8 PM....then from 8 PM - 5 AM it is back to 50 degrees ensuring that it stays off.
Probably still not fantastic for the electronics, but it IS a Harman bulletin, so this method is not entirely unsupported.

I'm doing something very similar with my Hastings St Croix, with good results. Basically you just have to keep in mind that your stove is not realy meant to be run the same way you'd run a forced hot water furnace. However, the auto on/auto off seems to be pretty low risk to me, and adds a huge measure of convenience. I'll post pics if I get a few minutes tonight, but the configuration is really very simple (just like in the bulletin).
Hoppe this helps

I think this paragraph is important and it could actually allow the stove to give more control to the t/stat;

If the stove is a manual ignite stove or an auto ignite stove with the auto-manual switch in manual mode, the
stove will go into a 4-blink status when the thermostat opens (is satisfied) and the stove will go to a
minimum burn and stay there until the thermostat closes (calls for heat). When the thermostat closes (calls
for heat) the 4-blink status will reset automatically

This is how a furnace works imo, the stove wouldnt actually shut down, it keeps the fire going with a minimal consumption of pellets and the t/stat could be programmed to keep the temp in the room by having the probe maybe set to just shy higher than what the t/stat would be programmed for.
This would save the igniter, electronics I believe and would help pellet consumption.
Opinions on this?

 

[mkmh]

Yep, I think you are on the right track with that. However, for my situation my preference is to just have the stove off for extended periods of time. For the space i'm heating even running it on low will provide more heat then I need, and will consume more pellets than i'm willing to part with

If you're comfortable with running the stove 24/7 then the programmable thermostat should be able to do a good job of maintaining an even temperature for you (assuming the stove is the right size for the space). Please let us know how it works out for you.

 

[Hammerjoe]

Truth is I havent made my decision yet.
I was actually today at Home Depot and was looking at getting one of these: http://www.ritetemp-thermostats.com/8085C.html
I know it is overkill but it looks fancy and it costs the same as the Honeywell RTH230b.

I didnt buy it because there was nobody at the place that could get me some 24 gauge twisted wire.


I am not sure what would be the best operation mode yet.
I still need to think about this more in dept.
Why would I need to plug the stove to a T/stat?

 

[Hammerjoe]

I bought the ritetemp t/stat and installe dit last night.
It works great.

I programmed it for my needs, basically, from 8 to 11 put temp at 30 degrees celsius and from 11 till 8pm at 16.5 and from 8pm till 1am again at 30c.

I thought initially on having the stove on manual mode, from what I could find it burns 0.75lbs/hour in maintenance mode (I guess that what it is) but I am not sure how much it needs to ignite.

Anyway, it works perfectly except for the stove that is, the stove thing failed to ignite this morning... the pot was full of pellets but it didnt ignite.

And this is the major problem that I have with this stove, its ignition is not reliable and I am always afraid that I will going to a cold home, because the stove failed to ignite.

 

[mkmh]

Hi Hammerjoe,

How old is your stove? I picked mine up used and it is about 5 years old (only 2 years of real use from what I was told). When I purchased it I noticed that igniter was extremely weak and unreliable so I purchased a new one from the dealer for about 60 bucks.
Here is the thread where a few of the experts helped me through that problem:
https://www.hearth.com/talk/threads/9189/

The first thing to check of course would be to make sure the area around the igniter is clean and free of ash.

 

[Hammerjoe]

The stove is three years old and had the ignitor replaced earlier this year.

That is the problem with this stove, I think the ignitor is not in the ideal position because of the ash amount and it defeats the purpose of an automatic ignition if every time the stove is off I need to clean the burn pot.

When the stove shuts off it burns all the pellets in the burn pot all the way down to the feeder.
Of course the burn pot will be full of ash and no doubt carbon deposits and that is what makes it hard to start, so when new pellets come in, there isnt enough draft to blow all the ash and of course the carbon deposits cant be removed without a good scrape.

The way I want the stove to be set up is, basically burning when I am home, makes it hard for me to do any cleanup except on the weekend when I am all day home.
So how can I fix this?

 

[pelletheat]

Did you ever check the line voltage at the wall outlet the stove is plugged into? Is the outlet grounded? No less than 116 volts should be going to the stove from the outlet, not enough juice will not get the igniter hot enough to light the pellets. Is there anything drawing power from the same outlet?
Just some things to check........

 

[mkmh]

When I replaced the igniter on mine I also removed the burnpot and drilled 4 extra holes an inch or so away from where the auger feeds. The dealer said that this would help with air flow (makes sense). So far no issues with it not starting up. I know what mean though about the leftover ash. I get that too, but with the new igniter and those holes I don't have any issues. I have been scraping out the pot about once per week.

If you do elect to remove the burnpot and drill the holes, you'll need to replace the gasket behind it. It should be about an hour job.

 

[Hammerjoe]

Good advice.

The stove is plugged directly to the wall, no other appliances sucking juice.
As for drilling new holes, thats a bit too much for me.

 

[Tristan]

Please help. I am trying to connect the setback t/stat to my Harman XXV. I am using Honeywell RTH230B for the tstat, I am using 18 ga (24 was not avail) thermostat wire. The bulletin states that 24 ga is minimum, since 24 ga is not avail, I though 18 would suffice. The tstat and the room sensor is connect in a series as state in he Harman bulletin. The tstat is program as directed in the bulletin. Everything is connected as it should be. However, when i turn the stove bAck on (room temp mode, with auto ignite) the blinking light (4 times) keeps blinking and does not reset as it should be. Hence the stove does not turn on. Please advise. What am I missing? Thank you.

 

[mkmh]

Well, the 4 blinks means something is amiss. Have you removed the jumper from the t-stat as mentioned in the bulletin?

 

[GVA]

Please help. I am trying to connect the setback t/stat to my Harman XXV. I am using Honeywell RTH230B for the tstat, I am using 18 ga (24 was not avail) thermostat wire. The bulletin states that 24 ga is minimum, since 24 ga is not avail, I though 18 would suffice. The tstat and the room sensor is connect in a series as state in he Harman bulletin. The tstat is program as directed in the bulletin. Everything is connected as it should be. However, when i turn the stove bAck on (room temp mode, with auto ignite) the blinking light (4 times) keeps blinking and does not reset as it should be. Hence the stove does not turn on. Please advise. What am I missing? Thank you.

4 blink means your room sensor is open....
you have it in series with a external t-stat now which means that the t-stat is saying your room is at temp and opening the circuit....
Try to manually adjust the t-stat to turn on and then go from there...

 

[Tristan]

One word. UNBELIEVABLE!! In the past I have had a multitude of successes with a variety of do-it-yourself projects around my house. I've finished a previously unfinished basement: framing, plumbing, electrical, heating, ventilation, drywall, cabinetry ... you name it, I've done it. So when I set out to perform this task of setting up the setback t/stat for my Harman XXV (which i installed myself) I thought that i would once again be successful. I was confident. I followed all specifications. To my dismay, alas, nothing. Nothing. Nothing but four blinking lights. For 3 hours I tried all sort of wiring configuration. Nothing. Today's outdoor temp was averaging 20 deg with bright sunshine. The house temp was dropping rapidly, down to 50. My wife and my three young children are about to come home to a frigid home. No heat. Nothing. Finally, something on the Honeywell t/stat blinked. The battery indicator blinked What? Are you kidding me? Ten minutes later, after a quick trip to a local quickymart and two new AA batteries. I installed the new batteries. HEAT I have heat. Batteries. Fresh Batteries. One word. UNBELIEVABLE!