Indoor wood boiler

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Cashius23

New Member
Feb 4, 2021
16
Iowa
Greetings. My wife and I just bought an acreage. The house has a propane boiler with an old Royall wood boiler piped in. Model number 6526 which I can’t find much info on. I’ll be tearing out the baseboard and boiler and going forced air. My question is can I use the wood boiler (if functional) to feed a coil in my supply plenum and possibly a heat exchanger on the domestic side for the water heater. Ive looked at the newer Royall manuals but haven’t really seen an indoor wood boiler piped this way with forced air. Wasn’t sure if this is the same as an outdoor boiler just inside. Just curious if anyone else does it this way or the proper way to pipe it. Thanks in advance
 
Last edited:

JMihevic

Member
Feb 3, 2018
24
Medina, Ohio
When I built my home in 1980, I installed a standard forced air heat pump system. I had the HVAC guys install a 22" X 27" 2 row hot water coil in the hot air plenum above the air handler. I installed a Tarm MB Solo 55 gallon wood boiler. I am now going on my 41st year with the system and am using it now to heat my home. I have used it every winter since the installation. In all those years I have never had to replace one single part on the Tarm system. In the worst winter we had, it was 20 degrees below zero and the Tarm was able to maintain my house at a comfortable 70 degrees.

I also heat all my hot water with the Tarm. I have an Amtrol 40 gallon "Boiler Mate" that has a hot water coil in the tank. The water temperature is maintained using a zone valve controlled by a thermocouple in the "Boiler Mate".

John M.
 
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SpaceBus

Minister of Fire
Nov 18, 2018
5,956
Downeast Maine
Why would you go forced air when you already have a good radiant system?
 

E Yoder

Minister of Fire
Jan 27, 2017
555
Floyd, VA
You should be able to plumb into a coil in the duct no problem.
 

maple1

Minister of Fire
Sep 15, 2011
10,783
Nova Scotia
Why would you go forced air when you already have a good radiant system?
Was kind of wondering that also. Usually see guys going the other way. But going either way would be a lot of work in a retrofit situation. Reasons must be really compelling?
 

Cashius23

New Member
Feb 4, 2021
16
Iowa
Was kind of wondering that also. Usually see guys going the other way. But going either way would be a lot of work in a retrofit situation. Reasons must be really compelling?
Personal preference really. More my wife. I’m more for just leaving it. I’m going to have a little more money into going forced air vs adding mini splits for cooling. I’ll do everything myself so I’m not paying company prices for anything. I’d have to add a zone in the basement anyways as I’ll eventually finish it. Circulating and cleaning air is nice sometimes. Plus easy to put a humidifier on. The boiler is older so id replace it anyways with a high efficient one. Either way I’m gonna spend some coin.
 

Cashius23

New Member
Feb 4, 2021
16
Iowa
When I built my home in 1980, I installed a standard forced air heat pump system. I had the HVAC guys install a 22" X 27" 2 row hot water coil in the hot air plenum above the air handler. I installed a Tarm MB Solo 55 gallon wood boiler. I am now going on my 41st year with the system and am using it now to heat my home. I have used it every winter since the installation. In all those years I have never had to replace one single part on the Tarm system. In the worst winter we had, it was 20 degrees below zero and the Tarm was able to maintain my house at a comfortable 70 degrees.

I also heat all my hot water with the Tarm. I have an Amtrol 40 gallon "Boiler Mate" that has a hot water coil in the tank. The water temperature is maintained using a zone valve controlled by a thermocouple in the "Boiler Mate".

John M.
Good to know thanks. The manual said something about a dump zone. What did you do for one if you have one?
 

JMihevic

Member
Feb 3, 2018
24
Medina, Ohio
Good to know thanks. The manual said something about a dump zone. What did you do for one if you have one?
This is a summary of my system:
- I set the Samson damper/draft regulator to control boiler water at 170 Deg F
- The water flow through the fan plenum coil I set to some minimum flow with a 10 turn trim valve
- A "zone bypass" valve around the trim valve is controlled and cycles from the house thermostat to maintain a constant house temp.
- If the boiler water temp > 200 Deg F the "zone bypass" is opened
- If the boiler water temp >220 I use a wireless "doorbell" ringer that is triggered by a Honeywell aquastat at 220 Deg F. The doorbell alarm rings in my bedroom
- Also, in my bedroom, is a "power out" alarm, at which time I go on generator power to run the boiler circulator and blower fan in the air handler.
- If everything fails, and I have to "dump" boiler heat, before the relief blows, I have connected the Tankless coil, that came with the Tarm boiler, to my water supply with the outlet (via a valve) to my basement drain. For the dump, I open the valve to the basement drain to cool off the boiler. I have considered automating this outlet dump valve with a solenoid valve to the basement drain, but haven't done that as yet.

John M.
 

Bad LP

Minister of Fire
Nov 28, 2014
1,603
Northern Maine
Was kind of wondering that also. Usually see guys going the other way. But going either way would be a lot of work in a retrofit situation. Reasons must be really compelling?
Instant heat is the short answer. I know a guy who did it but off his boiler. The one draw back to radiant floor heat is the long time to get a space satisfied.
Mine is stubbed with 3/4 on the manifold but no pipe or water coil should I want to do it.
 

3fordasho

Minister of Fire
Jul 20, 2007
1,001
South Central Minnesota
Good to know thanks. The manual said something about a dump zone. What did you do for one if you have one?
The most common cause of boiler overheat is a power failure. My set up has a 1000w pure sine inverter with built in transfer switch that with in miliseconds of a power failure seamlessly switches over to a 12V group 27 marine battery (deep cycle). The inverter also monitors battery condition and charges as needed. My boiler and the circulation pump only draw 85-90W when running so the battery will run it more than long enough for the fire to burn out. The inverter automatically switches back to grid power once it comes back on.

The other failure that could cause an overheat condition is a failed circulation pump. In this case I use the european overheat protection method and that is domestic cold water connected to the overheat coil built into the boiler. The water is controlled by a Watts STS20 thermostatic valve (the thermal bulb the valve comes with is installed into the boilers water jacket). The valve opens when temps get too high and flood the overheat coil with cold water, then out to a drain. No need for a bunch of tube and fin above the boiler and a valve to allow flow through it that a dump zone requires. The Watts STS20 valve requires no power or controls other than the thermostatic bulb it comes with.
 

JMihevic

Member
Feb 3, 2018
24
Medina, Ohio
. . . The other failure that could cause an overheat condition is a failed circulation pump. . .
So what fails on the pump? I am still on my original circulation pump after all these years. The only failure I had was when the "spring coupling" between the motor and the pump broke and the pump stopped. Now, I replace with a new coupling every few years. Once I start burning wood my circulator runs continuously. The motor is only on the start/centrifigal clutch once at start up. I oil the pump/motor bearings annually. I suppose the motor could just burn up and quit.

John M.
 

3fordasho

Minister of Fire
Jul 20, 2007
1,001
South Central Minnesota
So what fails on the pump? I am still on my original circulation pump after all these years. The only failure I had was when the "spring coupling" between the motor and the pump broke and the pump stopped. Now, I replace with a new coupling every few years. Once I start burning wood my circulator runs continuously. The motor is only on the start/centrifigal clutch once at start up. I oil the pump/motor bearings annually. I suppose the motor could just burn up and quit.

John M.
Hopefully they run forever. I run Grundfos Alpha 2 ECM circulators and they start and stop all the time depending where they are in the system. The alpha's have more electronics so I guess there is more to fail there. I just don't want a $175 circulator that fails to damage a $6-8K boiler. I only worry about the boiler to storage circulator, failure of the others in the system would just cause no heat delivery to loads.
 

Cashius23

New Member
Feb 4, 2021
16
Iowa
Interesting ways of doing that then.
This is a summary of my system:
- I set the Samson damper/draft regulator to control boiler water at 170 Deg F
- The water flow through the fan plenum coil I set to some minimum flow with a 10 turn trim valve
- A "zone bypass" valve around the trim valve is controlled and cycles from the house thermostat to maintain a constant house temp.
- If the boiler water temp > 200 Deg F the "zone bypass" is opened
- If the boiler water temp >220 I use a wireless "doorbell" ringer that is triggered by a Honeywell aquastat at 220 Deg F. The doorbell alarm rings in my bedroom
- Also, in my bedroom, is a "power out" alarm, at which time I go on generator power to run the boiler circulator and blower fan in the air handler.
- If everything fails, and I have to "dump" boiler heat, before the relief blows, I have connected the Tankless coil, that came with the Tarm boiler, to my water supply with the outlet (via a valve) to my basement drain. For the dump, I open the valve to the basement drain to cool off the boiler. I have considered automating this outlet dump valve with a solenoid valve to the basement drain, but haven't done that as yet.

John M.
So boiler loop is constantly circulating water and I’ll use the plenum coil and domestic water heat exchanger or whatever I decide to use as secondaries. That’s pretty much my biggest question. Then I’ll figure my dump zone. I always told myself when we found our forever home I’d put in a generator so hopefully losing power won’t be an issue eventually.
 

Cashius23

New Member
Feb 4, 2021
16
Iowa
The most common cause of boiler overheat is a power failure. My set up has a 1000w pure sine inverter with built in transfer switch that with in miliseconds of a power failure seamlessly switches over to a 12V group 27 marine battery (deep cycle). The inverter also monitors battery condition and charges as needed. My boiler and the circulation pump only draw 85-90W when running so the battery will run it more than long enough for the fire to burn out. The inverter automatically switches back to grid power once it comes back on.

The other failure that could cause an overheat condition is a failed circulation pump. In this case I use the european overheat protection method and that is domestic cold water connected to the overheat coil built into the boiler. The water is controlled by a Watts STS20 thermostatic valve (the thermal bulb the valve comes with is installed into the boilers water jacket). The valve opens when temps get too high and flood the overheat coil with cold water, then out to a drain. No need for a bunch of tube and fin above the boiler and a valve to allow flow through it that a dump zone requires. The Watts STS20 valve requires no power or controls other than the thermostatic bulb it comes with.
That’s pretty slick. Little cheaper than a generator anyways. I was thinking an actuator powered closed and opens on loss of power with temp switch in series but yours is a little simpler. Thanks
 

JMihevic

Member
Feb 3, 2018
24
Medina, Ohio
Interesting ways of doing that then.

So boiler loop is constantly circulating water and I’ll use the plenum coil and domestic water heat exchanger or whatever I decide to use as secondaries. That’s pretty much my biggest question. Then I’ll figure my dump zone. I always told myself when we found our forever home I’d put in a generator so hopefully losing power won’t be an issue eventually.
Yes, the plenum loop is my main loop. An important thing for me was to put "balancing cocks" in every loop to adjust the water flow. For example, in my "Boiler Mate" hot water loop I adjust the flow so that a cold tank will heat 40 gallons in one hour to 120 degrees. The flow in any secondary loop is set not to put a large load change on the boiler. This reduces thermal shock to the boiler and allows the Samson damper/draft regulator to maintain good control. The boiler water temperature does not vary more than 5 degrees from setpoint (170 Deg.). The bypass zone valve that is controlled by the house thermostat rarely cycles, because I am accustomed to how much flow I set the on the 10 turn trim valve based on the outdoor air temperature. This way, the heat flow into the house from the boiler equals the heat loss to the outside and the house stays at a very comfortable uniform temperature.
 

Cashius23

New Member
Feb 4, 2021
16
Iowa
Yes, the plenum loop is my main loop. An important thing for me was to put "balancing cocks" in every loop to adjust the water flow. For example, in my "Boiler Mate" hot water loop I adjust the flow so that a cold tank will heat 40 gallons in one hour to 120 degrees. The flow in any secondary loop is set not to put a large load change on the boiler. This reduces thermal shock to the boiler and allows the Samson damper/draft regulator to maintain good control. The boiler water temperature does not vary more than 5 degrees from setpoint (170 Deg.). The bypass zone valve that is controlled by the house thermostat rarely cycles, because I am accustomed to how much flow I set the on the 10 turn trim valve based on the outdoor air temperature. This way, the heat flow into the house from the boiler equals the heat loss to the outside and the house stays at a very comfortable uniform temperature.
Ah ok so your using circuit setters for constant flow and depending on outdoor temp you open or close it to increase or decrease your flow. Bit of a learning curve but probably nice once you get it dialed in.
What would you consider a large load change on the boiler? Could a guy put in a thermostatic mixing valve in to control return temp if it were to get to low? Pretty much like you would do on a non condensing boiler to keep the return water temp above 140 degrees?
 

JMihevic

Member
Feb 3, 2018
24
Medina, Ohio
Ah ok so your using circuit setters for constant flow and depending on outdoor temp you open or close it to increase or decrease your flow. Bit of a learning curve but probably nice once you get it dialed in.
What would you consider a large load change on the boiler? Could a guy put in a thermostatic mixing valve in to control return temp if it were to get to low? Pretty much like you would do on a non condensing boiler to keep the return water temp above 140 degrees?
The learning curve isn't bad at all. I am amazed that my house temp is more constant with the wood boiler operation than with my heat pump which cycles ON/OFF based on a thermostat that inherently has a fixed dead band.
My biggest load change is when the house thermostat calls for the bypass zone to open and my grand daughter is sitting in the shower with hot water running continuously. Even then there is no problem with the boiler maintaining supply water temp. I had considered an auto mixing valve, controlling the return water, as that was what they did in the article in the Oct 1979 issue of Popular Mechanics. I thought about how I would design my system and decided against that. I did have a concern if, In real mild weather, with a low flow requirement, that the pump would be close to "deadheaded". So I have a shunt line from supply to return with a fixed amount of flow to keep the pump happy at all times.

John M.
 

Cashius23

New Member
Feb 4, 2021
16
Iowa
The learning curve isn't bad at all. I am amazed that my house temp is more constant with the wood boiler operation than with my heat pump which cycles ON/OFF based on a thermostat that inherently has a fixed dead band.
My biggest load change is when the house thermostat calls for the bypass zone to open and my grand daughter is sitting in the shower with hot water running continuously. Even then there is no problem with the boiler maintaining supply water temp. I had considered an auto mixing valve, controlling the return water, as that was what they did in the article in the Oct 1979 issue of Popular Mechanics. I thought about how I would design my system and decided against that. I did have a concern if, In real mild weather, with a low flow requirement, that the pump would be close to "deadheaded". So I have a shunt line from supply to return with a fixed amount of flow to keep the pump happy at all times.

John M.
Interesting. You could always get a heat pump with a variable speed compressor. Spendy but they’ll maintain vs on/off with a few degree temp swing.
Thanks for the boiler tips. Now I’ve got a direction to start in
 

JMihevic

Member
Feb 3, 2018
24
Medina, Ohio
One more thing I want to mention on my installation. When I ordered my two row hot water coil for the plenum, I didn't specify how to configure the flow through the coil. It came with both rows in parallel with water in on one side and water out on the other. When I cut the flow down on mild days, the water goes in at 170 Deg and comes out at room temperature. As a result there is a temperature gradient across the hot air plenum with the air coming out of the registers warmer on one side of the house than the other. I don't know, but, if I could have specified the water in and water out to be at opposite sides of each coil I think I would have a more even temperature distribution of the heated air to the house.

John M.
 

Cashius23

New Member
Feb 4, 2021
16
Iowa
One more thing I want to mention on my installation. When I ordered my two row hot water coil for the plenum, I didn't specify how to configure the flow through the coil. It came with both rows in parallel with water in on one side and water out on the other. When I cut the flow down on mild days, the water goes in at 170 Deg and comes out at room temperature. As a result there is a temperature gradient across the hot air plenum with the air coming out of the registers warmer on one side of the house than the other. I don't know, but, if I could have specified the water in and water out to be at opposite sides of each coil I think I would have a more even temperature distribution of the heated air to the house.

John M.
It looks like most coils I’ve seen are that way. Never would have thought about that honestly. Thanks for that.
 

Cashius23

New Member
Feb 4, 2021
16
Iowa
Just figured I’d update. I talked my wife into keeping the baseboard. I put a ducted minisplit in to give the bedrooms and laundry room AC so she’s happy. I’ve decided on an outdoor boiler. Did tons of research and hours of reading and figured an indoor boiler just isn’t what I want. Finally got a little time and started tearing into the old boiler in the basement. No idea how I’m getting it out. Probably going to cut it up. But the stack was pretty full of creosote and so was the inside of the boiler. Not sure if I would’ve wanted to fire that thing or not after looking at all that.

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SpaceBus

Minister of Fire
Nov 18, 2018
5,956
Downeast Maine
Before you cut up all the indoor boiler stuff, are you sure you want an outdoor system? That boiler got all covered in creosote because it wasn't being burned appropriately. An indoor boiler really needs storage to not accumulate tons of creosote and smoke up your outdoor space. Outdoor boilers don't always need storage, but you will have to add a lot of plumbing. With your house being already set up for the indoor boiler, I would be figuring out a way to get storage in there and just burn the old boiler.
 
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peakbagger

Minister of Fire
Jul 11, 2008
6,351
Northern NH
My indoor boiler looked like that when I got it. Once I started running it right it cleaned right up. Once I added 550 gallons of storage, no creosote. My house is 30 years old with an "ideal chimney" (30' tall masonry with all but 4' sticking outside at the ridgepole). I have only swept the chimney three times. Not because it needed it but because I felt guilty.
 

Cashius23

New Member
Feb 4, 2021
16
Iowa
That's a few years of smoldering!

Out of curiosity what outdoor boiler are you looking at? And have you thought about storage with it?
Still researching some brands. I like the crowns. There’s a Heatmor dealer 15 minutes away so might stop there and have a look. Tons of central boilers around here.


Before you cut up all the indoor boiler stuff, are you sure you want an outdoor system? That boiler got all covered in creosote because it wasn't being burned appropriately. An indoor boiler really needs storage to not accumulate tons of creosote and smoke up your outdoor space. Outdoor boilers don't always need storage, but you will have to add a lot of plumbing. With your house being already set up for the indoor boiler, I would be figuring out a way to get storage in there and just burn the old boiler.
A propane tank is out of the question as it wouldn’t fit. The only way would be if I build one or buy smaller storage tanks somewhere. I also don’t know how much storage I would need. I know my heat loss and everything I just need to figure it. I’d have to feed the wood through a window somewhat close to the boiler otherwise haul it downstairs and across the living room to the boiler room. I’ve got a shop I’d also like to heat is another factor for ditching the indoor.
My indoor boiler looked like that when I got it. Once I started running it right it cleaned right up. Once I added 550 gallons of storage, no creosote. My house is 30 years old with an "ideal chimney" (30' tall masonry with all but 4' sticking outside at the ridgepole). I have only swept the chimney three times. Not because it needed it but because I felt guilty.
550 works good for you? Seems like most people say at least 1000 gallons. Can a guy even clean that out I’ve never dealt with a chimney this bad. This boiler is from the 70s.