Homemade outdoor boiler controls.

Joe Hillmann · August 11, 2014, 04:55:45 PM

I am building an outdoor boiler. I think I have it all figured out but figured I would run it past you guys to see if it will work. I don't have any concerns about building the boiler, my concerns are the controls for it.

My plan is to have it set up with natural draft (no fan blowing into the fire box). I plan to use an aquastat to control two dampers, one on the air into the fire box and one on the chimney on the way out of the fire box. When the aquastat says it is too cold the dampers will open and when it is at the set temp they will close. I already have a couple aquastats(I'm not sure what voltage they are for) and two honeywell 90 degree damper control that are set up for 24 volt. I will have to put something between the aquastat and damper controls if the aquastat can't run on 24 volts.

For the furnace I plan to put a heat exchanger in the plenum of my furnace. I will have two thermostats one that I have now to control the furnace will be set at a low temperature and on for the wood boiler that will be set to the temp I want in the house. When the wood boiler one calls for heat I assume I will wire it so the circulating pump turns on and just the blower fan in the furnace as well.

Am I overlooking anything when it comes to controlling the boiler?

Also if in the future I wanted to put radiant floor heat in or hot water radiators how do I set up the temp and pump control on that? I assume due to the long time from when it starts heating till the heat is actually felt that a regular thermostat isn't used?

WmFritz · August 11, 2014, 06:21:17 PM

Joe, I'm just thinking out loud, but I don't think that the natural draft firebox would keep up to your heat load. I may be wrong, but let's say your boiler water temp satisfies the aqua stat, closes the dampers and the fire idles down to coals. Later, when the house calls for heat and the dampers reopen, I would think it would take too long to get that fire hot enough to raise the boiler temp quick enough.

I would eliminate the chimney damper and put an induction blower on you design.

I have the t-stats set up on my forced air furnace the way you described and it works well.

As far as your radiant add-ons; one option is to use zone valves with t-stats. I have radiant heat in my cabin and this controller made everything much easier for my install.

http://www.pexuniverse.com/store/category/taco-zone-valve-controls

Joe Hillmann · August 11, 2014, 10:02:03 PM

I don't think when the furnace blower in the furnace and the pump kicks in the water temp will drop too much. The boiler should hold about 275 gallons of water so it should stay pretty steady even when the house is calling for heat. But if it ends up cooling too fast I could always add on a blower in the door. I am more concerned about closing both dampers and the fire dieing down to just a few coals, I may need a blower to get it lit back up again. That is something I won't really know until I build it though.

Hilltop366 · August 11, 2014, 10:04:04 PM

I think the blower will blow cold air at first unless you put a aqua stat in the plenum coil to control the blower.

Jim H · August 12, 2014, 07:26:01 AM

I'd keep an eye on the damper in the chimney, it seems like creosote build up could cause it to stick.

Hilltop366 · August 12, 2014, 09:02:53 AM

If you were to use the circulator power to open the dampers the fire would have a head start, it would still need a high / low limit in the circuit.

Ivan49 · August 12, 2014, 09:49:44 AM

I don't really know about not having a blower but I don't think it would keep up on really cold winters. I idea behind the blower is quick on and then off to get instant heat. I will only cost you about 100.00 more for the blower and solonid to operate it. As for putting anything inside the smoke stack DON'T DO IT. You will thank me when you do't have to climb up there and try and get it out on a -20 day with the worst snow store of the year. It is a creosote trap I know first hand. I have built 4 of these and they are all still running after 10 years or more. I thought the damper inside was a good idea until it plugged everything up. Keep your wiring simple and make a print out of your wireing diagram so you you know later down the road how you did it

Gary_C · August 12, 2014, 10:55:05 AM

You need to run your circulator pump all the time, not just when you need heat. Temperature differences with your boiler and the rest of the system will cause a lot of expansion and contraction and that is bad.

Joe Hillmann · August 12, 2014, 11:17:11 AM

Quote from: Hilltop366 on August 11, 2014, 10:04:04 PM
I think the blower will blow cold air at first unless you put a aqua stat in the plenum coil to control the blower.

I am pretty sure the first couple minutes it will blow cold air. I am not sure how to set it up so that when the thermostat in the house calls for heat that the pump will turn on and the blower will wait until the heat exchange is warmed up. I could figure out how to do it with a simple aquastat if I didn't use the same blower when the furnace is running on natural gas.

Joe Hillmann · August 12, 2014, 11:18:09 AM

Quote from: Jim H on August 12, 2014, 07:26:01 AM
I'd keep an eye on the damper in the chimney, it seems like creosote build up could cause it to stick.

I will keep an eye on that or may leave it out all together and just have the damper on the intake.

Joe Hillmann · August 12, 2014, 11:20:51 AM

Quote from: Hilltop366 on August 12, 2014, 09:02:53 AM
If you were to use the circulator power to open the dampers the fire would have a head start, it would still need a high / low limit in the circuit.

You mean, have it set up so when the water pump turns on the dampers open as well? I will look into how I would hook that up and still be able to over ride it if it gets to hot or cold.

Joe Hillmann · August 12, 2014, 12:26:25 PM

Quote from: Ivan49 on August 12, 2014, 09:49:44 AM
I don't really know about not having a blower but I don't think it would keep up on really cold winters. I idea behind the blower is quick on and then off to get instant heat. I will only cost you about 100.00 more for the blower and solonid to operate it. As for putting anything inside the smoke stack DON'T DO IT. You will thank me when you do't have to climb up there and try and get it out on a -20 day with the worst snow store of the year. It is a creosote trap I know first hand. I have built 4 of these and they are all still running after 10 years or more. I thought the damper inside was a good idea until it plugged everything up. Keep your wiring simple and make a print out of your wireing diagram so you you know later down the road how you did it

You are the second person to say not to put a damper on the chimney due to build up. I won't put one in but build it in a way that I can put one in if I decide it is necessary to damper down the fire. I will also put a bit more effort than I would have otherwise to make sure the door is as airtight as I can get it. That should reduce the need for a damper in the chimney.

I am not, not putting in a blower to avoid the cost it is more that I want to keep it as simple as I can for now. I can always add one if necessary.

Joe Hillmann · August 12, 2014, 12:27:20 PM

Quote from: Gary_C on August 12, 2014, 10:55:05 AM
You need to run your circulator pump all the time, not just when you need heat. Temperature differences with your boiler and the rest of the system will cause a lot of expansion and contraction and that is bad.

How do regular factory built boilers work? Do the pumps run all the time or only when heat is called for?

thecfarm · August 12, 2014, 12:56:47 PM

My pumps run all the time. On my Heatmor I have no damper in the chimney. The fire is smothered out in between cycles. When I first got it,I would check the fire and think it had gone out. It's all black when I open the door.But I do have the fans that drives oxygen into the firebox. I myself would not want to go back to a natural draft. I had an indoor one at my other house,natural draft and damper in the stove pipe. It did ok,but the fans do much,much better. My smoke goes the full length of the furnace,towards the front, goes into about a 8 inch round opening,there is a 4X6" rectangle opening,than goes all the way to the back and out through the chimney.

Hilltop366 · August 12, 2014, 01:57:27 PM

Quote from: Joe Hillmann on August 12, 2014, 11:17:11 AM
Quote from: Hilltop366 on August 11, 2014, 10:04:04 PM
I think the blower will blow cold air at first unless you put a aqua stat in the plenum coil to control the blower.

I am pretty sure the first couple minutes it will blow cold air. I am not sure how to set it up so that when the thermostat in the house calls for heat that the pump will turn on and the blower will wait until the heat exchange is warmed up. I could figure out how to do it with a simple aquastat if I didn't use the same blower when the furnace is running on natural gas.

I think you could use the same blower and have more than one way to turn it on, however if you end up having the circulator on all the time there will be no cold air.

Quote from: Joe Hillmann on August 12, 2014, 11:20:51 AM
Quote from: Hilltop366 on August 12, 2014, 09:02:53 AM
If you were to use the circulator power to open the dampers the fire would have a head start, it would still need a high / low limit in the circuit.

You mean, have it set up so when the water pump turns on the dampers open as well? I will look into how I would hook that up and still be able to over ride it if it gets to hot or cold.

Yes in the same way a oil boiler will turn on the burner when there is a call for heat even though it is not at the low limit. I think this is how my brothers Kerr wood boiler works with a electric draft control, I will ask him to be sure. My Tarm boiler has a non electric draft control so I live with the lag time.

Another thing that the Kerr boiler has that I though was kind of neat is the temp / pressure blowoff valve is plumed to the fire box so that if a over heat or over pressure condition occurs it dumps the water on the fire.

Gary_C · August 12, 2014, 03:02:15 PM

Quote from: Joe Hillmann on August 12, 2014, 12:27:20 PM

How do regular factory built boilers work? Do the pumps run all the time or only when heat is called for?

All the outdoor boilers I know of, including my CB, have the circulator pump running all the time. If you don't run the circulator pump all the time you will have serious temperature differentials within the stove and in the lines to the house. I believe CB has even gone to a mixing valve on the return lines to prevent the cold shock of returning water from doing damage to the water jacket of the boiler.

doctorb · August 12, 2014, 03:17:57 PM

It seems to me that, if your system is set up to exchange heat with your indoor oil burner, that the temp of the water jacket in the indoor boiler will get too low, and take too long to reheat, if you do not run the OWB circulator pumps all the time. This will lead to a delay of your system's ability to deliver heat when your indoor thermostats call for it. This is why most systems have a circulator pump on the indoor furnace side, to make sure the water jacket stays at a more constant temperature. Just my thoughts.

Joe Hillmann · August 12, 2014, 03:41:13 PM

Quote from: doctorb on August 12, 2014, 03:17:57 PM
It seems to me that, if your system is set up to exchange heat with your indoor oil burner, that the temp of the water jacket in the indoor boiler will get too low, and take too long to reheat, if you do not run the OWB circulator pumps all the time. This will lead to a delay of your system's ability to deliver heat when your indoor thermostats call for it. This is why most systems have a circulator pump on the indoor furnace side, to make sure the water jacket stays at a more constant temperature. Just my thoughts.

The natural gas furnace inside the house isn't a boiler, it is a forced air system. I plan to put a heat exchanger in the plenum of the furnace and plumb the outdoor boiler to the heat exchanger. I will then use the blower on the furnace to move the heat through the building.

albirk · August 13, 2014, 04:08:23 AM

leave your pump run 24\7 add a side arm to your water heater for your domestic hot water all the old CB classic boilers are natural draft no fan and they work fine just make sure you don't boil the stove over mine has 195 max water temp

tractorman44 · August 14, 2014, 08:09:22 AM

You should NOT even consider an automatic damper in the flu pipe for the above listed reasons....my .02 worth.

What you may consider would be a simple aquastat to turn on the pump when the supply side of the boiler piping warms and off as it cools with diminishing fire. Parallel those contacts with a simple "outdoor" thermostat that closes on a drop in temp and set that control at 32 degrees to start the pump to get water moving in case of extended "no-fire" time in the middle of winter. Consider this basic "freeze control". Of course this is not needed if you are circulating Propylene Glycol.

The above aquastat will start and run the pump 24/7 as long at the water is in between on/off temps. Now, the kicker.... consider a "bypass" or "diverter" valve (24v) piped in the circuit at the air handler (gas furnace in your case). It is a simple three pipe valve, one to the supply and one to the coil and the other back into the return line giving continual flow of hot water within a few feet of the heating coil. This bypass, diverter valve or three way valve will be controlled by your room thermostat.

Consider a "timed on" 24v relay wired in parallel with the three way valve to close a set of contacts to energize your air handler blower. The bit of a delay in "fan on" condition will allow the three way to fully open to the coil, close to the return line and have a full head of hot water INSIDE your heat exchanger by the time the blower starts. No blast of cold air would be the result. When the thermostat satisfies, the three way goes back into bypass mode.

Are you building a pressurized hot water boiler or atmospheric with a vented reservoir ??

Joe Hillmann · August 14, 2014, 11:39:37 AM

Quote from: tractorman44 on August 14, 2014, 08:09:22 AM
You should NOT even consider an automatic damper in the flu pipe for the above listed reasons....my .02 worth.

What you may consider would be a simple aquastat to turn on the pump when the supply side of the boiler piping warms and off as it cools with diminishing fire. Parallel those contacts with a simple "outdoor" thermostat that closes on a drop in temp and set that control at 32 degrees to start the pump to get water moving in case of extended "no-fire" time in the middle of winter. Consider this basic "freeze control". Of course this is not needed if you are circulating Propylene Glycol.

The above aquastat will start and run the pump 24/7 as long at the water is in between on/off temps. Now, the kicker.... consider a "bypass" or "diverter" valve (24v) piped in the circuit at the air handler (gas furnace in your case). It is a simple three pipe valve, one to the supply and one to the coil and the other back into the return line giving continual flow of hot water within a few feet of the heating coil. This bypass, diverter valve or three way valve will be controlled by your room thermostat.

Consider a "timed on" 24v relay wired in parallel with the three way valve to close a set of contacts to energize your air handler blower. The bit of a delay in "fan on" condition will allow the three way to fully open to the coil, close to the return line and have a full head of hot water INSIDE your heat exchanger by the time the blower starts. No blast of cold air would be the result. When the thermostat satisfies, the three way goes back into bypass mode.

Are you building a pressurized hot water boiler or atmospheric with a vented reservoir ??

I plan on building the boiler so it is vented to the atmosphere. Someone else had suggested setting it up so if it boils over it boils over into the fire box to put the fire out. I think that is a good way to do it and will probably set mine up like that.

I plan to use used antifreeze for the fluid (you used to be able to get it for free from implement dealers in the area, by giving it away they didn't have to pay to get rid of it) I don't know it that is still the case any more though.

To keep things as simple as I possibly can, for now I think I will set it up so the pump is always on and an aquastat controls the damper on the door. Once/if I get that working I then may put more thought/money into it by setting up automatic controls for other things. I don't know what the power draw on a circulating pump is but I am pretty sure it will be much cheaper to run one 24/7 than to pay for natural gas to do all the heating.

Hilltop366 · August 14, 2014, 12:03:06 PM

I don't know what the power draw on a circulating pump is but I am pretty sure it will be much cheaper to run one 24/7 than to pay for natural gas to do all the heating.
[/quote]

If I did it right , a 1 amp draw @ $0.12 per kilowatt hour would be around $10.00 per month running 24/7. (my pump is a little less than 1 amp)

JSNH · August 21, 2014, 05:16:13 PM

I have a central boiler 5036 and it uses a damper with out a blower. A controler opens a seloniod that opens the damper to get air into the fire box. It works great. The controller is made by love and sold by Dwyer it is the TS2-10 model $45 its pretty easy to program and it is the same as stock but with a red display. You need to add the temp sensor and the well it goes into. Central boiler also has a cheep snap action switch in line to the damper so if the water goes over temp (maybe 205?) the curcuit opens till the temp comes down. It's a fail safe in case the controler shorts and keeps on providing power to keep the door open. I have never see it happen but its not a bad idea to have a redudant over temp control.

http://www.dwyer-inst.com/Product/Temperature/Switches/DigitalPanelMount/SeriesTS2

WmFritz · August 21, 2014, 11:49:22 PM

Quote from: Joe Hillmann on August 12, 2014, 03:41:13 PM

The natural gas furnace inside the house isn't a boiler, it is a forced air system. I plan to put a heat exchanger in the plenum of the furnace and plumb the outdoor boiler to the heat exchanger. I will then use the blower on the furnace to move the heat through the building.

My system is set up the same way. Like thecfarm, I run my pump through the h/x nonstop. My pump uses about the same electricity as Hilltops... maybe $10.00 a month.

I have no firsthand experience with using automotive antifreeze, but over the last few years of studying boiler setups, I've read many negative comments on using it.

thecfarm · August 22, 2014, 05:12:02 AM

[quote author=Joe Hillmann link=topic=76995.msg1168766#msg1168766 date=1407872473

The natural gas furnace inside the house isn't a boiler, it is a forced air system. I plan to put a heat exchanger in the plenum of the furnace and plumb the outdoor boiler to the heat exchanger. I will then use the blower on the furnace to move the heat through the building.
[/quote]

That's how I had the guy do mine. I can still use the oil furnace. But I don't.