Need some help visualizing a Central Boiler setup...

[IchWarriorMkII]

My father has a Woodmaster OWB, and he likes, but has some complaints about it and said he would probably look hard at another OWB brand before going with a Woodmaster again. Since Im in the market for an OWB, I've done some reading and I think that a Central Boiler is probably going to solve the few complaints my father has had about his Woodmaster... as well as a closer Dealer.

Anyways, my house is heated off of Forced air, heated via propane. Im trying to better understand how a central boiler would interface with this heater. Im assuming the heater has a thermostat that will blow the fan w/o firing the propane burner if its at a set temperature?

I understand that the CB has a type of radiator, which pumps hot water through to heat the air before being ducted to the house. Would the in house heater then operate as strictly a blower to move air throughout the house?

Also, it appeared that the CB diagrams ran the hot water through the domestic water heater before running in through the forced air heat exchanger, is that the case, or did I misunderstand their small grainy diagrams?


Thanks in advance!

 

[Butch(OH)]

I have forced air gas heat and a Woodmaster outside. The Woodmaster or most other outdoor boilers have separate controls that keep the circulating water between x and x temp. This is a totally separate operation from your home heat demands and it circulates continuously, no matter what your heat demands are. The heat exchanger goes in the warm air plenum and you run the blower (only)with a separate thermostat. Back up is your original furnace set a few degrees under the boiler 'stat. Yes the incoming boiler water goes through the domestic heat exchanger first. I am curious, being a Woodmaster owner what issues your Father in law has with his.

 

[highpower]

OK, now I have a couple questions.

" it circulates continuously, no matter what your heat demands are"

Your pump runs continuously even if the blower is not running on your furnace?

"the incoming boiler water goes through the domestic heat exchanger first"

The domestice hot water does not heat seperatly?

Just curious. My OWB (Hardy) only pumps water for heat only when the thermostat calls for heat. The blower on the central unit comes on at the same time.
My hot water goes through a coil of copper in my OWB storage tank before going into the hot water heater preheating it when the hot water is turned on in the house.

 

[IchWarriorMkII]

His problems were caused from excessive creosote build up from burning pinion pine trees. Other than that he likes it just fine. I think its an issue with the way its baffled... Ill ask again tomorrow.

Anyways, the forced air system should just operate the blower if the wood boiler has the radiator up to temp?

Ill look at my heater tomorrow to get a better mental picture. Although, I might want to just buy a newer unit, thats a lot quieter if its going to be doing the heating now, instead of my indoor wood stove :hmm3grin2orange:

 

[grandpatractor]

boiler water route

I have one also,its and empyre but most are set up similar.
water is continuously pumped between the house and the owb.
this keeps water from freezing in the line anywhere and also keeps the temp in the boiler more even with water flow.
when it comes in the house it goes
1 The heat exchanger in the forced air unit
2 The plate cooler before the hot water heater
3 The infloor heat manifold. which has a seperate thermostat and pump if heat is called for in its zone. otherwise the water just flows past it.

The pumps draw very little power.

 

[windthrown]

CB owner here...

Maybe I can answer some of your questions. I installed a Central Boiler unit here over a year ago. We are quite happy with it, though it does eat a lot of wood. We get free wood here in the land of tall timber though, and my girlfriend and I can easilly scavange good firewood from around here. Burning alder, madrone and oak will result in very little creosote forming. Burning Doug fir results in some creosote buildup, but it easilly flakes and sluffs off with a hoe or a shovel scraped against the insides of the boiler. It will burn up in the askes. I usually mix fir and the other hardwoods and there is only a thin layer of creosote at most. We also mostly burn dry seasoned wood, though at times we burn wet and even green wood which also result in more creosote building up.

I had to custom design/splice the OWB into our existing house heating system as CB did not have a diagram or design plan with our type of system. We already had a circulating pressurised hydronic electric floor heater and a separate solar hot water pre-heating system in the house. Our system uses two heat exchangers (HX) off the OWB line. The first HX (hottest) that the boiler PEX lines run to is a flat plate HX in a 'passive' convection loop on the electric hot water heater (typical design is on the Cb web site). The second HX is molre complex. It is in the floor loop in series with the original electric boiler. I called CB to size and special order the large flat plate HX in the floor loop based on the size of the existing electric heater. They matched it really well. The floor loop is pressurised and driven by a 009 Taco pump. I added a mixing valve just after the HX in the floor loop to mix cooler return floor line water and hot HX water. It is a Honywell mixing valve designed for hydronic flooring, and has adjustments for 100-140 degree F temps. Generally 100 F is for tile and wood floors like we have, and up to 140 F with heavy padded carpeting. When the thermostat goes on in the house, it just turns on the Taco pump and circulates the 100 F water in the house.

The OWB loop runs off a 007 Taco pump, and it runs all the time. The CB can be set at a temp range of 165 to 195. The factory setting is 185. The CB has a passive damper air duct that is not fan driven, though you can get one from them if you want one. You will not need it though. When the aquastat reads 10 degrees below the setting, the damper is opened. Often times the temp will drop another 5 degrees or so before the fire kicks the heat back up. The damper stays open until the temp setting is reached. When the damper closes you will often get a 5 degree overshoot by the time the fire dies down from being air starved. This means that you gat a range of heat from 15 degrees below the setting to 5 degrees above. I run it at 165, as our needs are for hot water are less with only 2 people living here, and we have hardwood floors and tile so we only need 100 F floor loop temps. Basic rule of thumb of a water-water HX is that you will get a 20 degree drop across the plates. With our setting at 165 F, we range from 150 F to 170 F degree water in the boiler loop under typical operation, so 130 to 150 F heat for the hot water heater convectin loop. The temp in the OWB loop drops after the hot water HX, but we only need 100 F mixed temp on the floor loop. Supposedly running it at 185 will be more efficient, but we do not need that much heat here. We are in a rather mild climate of Oregon, and 15 degrees F is about as cold as it gets here. It is supposed to get down to 17 F here tonight, and it snowed all day here today which is unusual for this area.

Anyway, some other things to consider with an OWB. If the fire dies out on a really cold night or we forget to load it with wood, then the temp can and will drop a lot lower. In that case, the hot water HX will reverse and wind up heating the house... and the boiler loop. This also acts as an antifreeze system for the boiler and PEX lines too. The boiler will not freeze, as there is a lot of water in there. The PEX lines would freeze first though, and maybe blow a brass fitting or PEX ring clamp in the process. In the reverse, if the system gets too hot it will boil over. When it boils over, nothing much happens. We had a bad damper that did not close right (replaced by CB) on the system and it boiled over a few times last year. The process of boiling over takes a lot of heat away (phase change from water to steam) and the water and steam just gush out the top vent port for a minute or so. After ot settles down just top up the boiler with water and look for teh casue of the boilover. CB uses a non-pressure system and that is the only way to go. It is fail-safe. CB has a UL sticker for that reason.

From what I gather from your post, in your case you would run the hot water HX the same, then use a water to air HX in an air duct with a fan system to blow the warm air into your existing heating duct system. CB has a design diagram for that on their site. You would also run your CB a lot hotter than I do as you need more heat in a water-air HX. Other than that, its all pretty straight forward.

Hope this helps. I gott'a throw some more wood into the OWB now...

 

[highpower]

With your circulation pump continually running, is that not wasting BTU's on the round trip from OWB to the house, would this not burn a lot more wood? Not knocking the system just curious.

My OWB has 110 gallons of water sitting until my thermostat cuts on the pump, at the same time a relay turns on the blower in my forced air system to blow air through the exchanger. The damper is the same as the rest, it only opens when the water temp goes below 170F. It does have a blower to force air under the fire to recover faster.

There is no danger of the supply lines freezing here as the frost line is only 10" or so. All my lines are at 2' except where they go into the back of the OWB.

 

[Butch(OH)]

OK, now I have a couple questions.

" it circulates continuously, no matter what your heat demands are"

Your pump runs continuously even if the blower is not running on your furnace?

"the incoming boiler water goes through the domestic heat exchanger first"

The domestice hot water does not heat seperatly?

Just curious. My OWB (Hardy) only pumps water for heat only when the thermostat calls for heat. The blower on the central unit comes on at the same time.
My hot water goes through a coil of copper in my OWB storage tank before going into the hot water heater preheating it when the hot water is turned on in the house.

Your pump runs continuously even if the blower is not running on your furnace? Yes

The domestice hot water does not heat seperatly? You lost me there but I believe your Hardy has a domestic coil in the furnace correct? Not many others do it that way. A plate type, or side arm is installed at the water heater and the circulating water flows through them to heat the domestic water.

 

[Butch(OH)]

His problems were caused from excessive creosote build up from burning pinion pine trees. Other than that he likes it just fine. I think its an issue with the way its baffled... Ill ask again tomorrow.

Anyways, the forced air system should just operate the blower if the wood boiler has the radiator up to temp?

Ill look at my heater tomorrow to get a better mental picture. Although, I might want to just buy a newer unit, thats a lot quieter if its going to be doing the heating now, instead of my indoor wood stove :hmm3grin2orange:

"Anyways, the forced air system should just operate the blower if the wood boiler has the radiator up to temp?"
Answer, Yes for the system to be more idiot proof the fan would not come on until you had X temp in the circulating water. I didn't want the added electrical controls and potential future problems and went with the simple route. When firing up (once so far this season) I simply left the house thermostat down until I had proper temps in the loop water. If my fire goes out the fan will come on and call for heat but there wont be any to get thus it will run continuously but when the temp drops a couple degrees the gas furnace thermostat will cause the gas burner to light and heat will be provided. Wife or me will notice the fan running all the time and simply lower the boiler stat, fan shuts off and gas furnace works the same as no boiler system. The Woodmaster has a controll setting that shuts the draft when the loop gets down to 120 to conserve the heat when the wood supply is exhausted.

I had questions about the exchanger being hot all the time and controlling the house heat by fan only but the system works perfectly, we could not be happier with our system.

Lots of folks purchase wood heaters and go gung hoe for a year or two then let them rust away while spending the wood cutting and splitting season watching TV. A person who does not want to spend some time working with his heating system should not consider an outdoor boiler, nor any other wood heat for that matter IMO.

Off my box, LOL

 

[grandpatractor]

With your circulation pump continually running, is that not wasting BTU's on the round trip from OWB to the house, would this not burn a lot more wood? Not knocking the system just curious.

The lines running to and from the house are in a black tile line and insulated. You will get a little bit of loss but it is minimal. My lines are down 2' and many years the frost will go deeper here. There is also area that the lines go into and out of the boiler that may not be insulated that could freeze if the flow stopped

 

[windthrown]

For a few gallons more...

With your circulation pump continually running, is that not wasting BTU's on the round trip from OWB to the house, would this not burn a lot more wood? Not knocking the system just curious.

My OWB has 110 gallons of water sitting until my thermostat cuts on the pump, at the same time a relay turns on the blower in my forced air system to blow air through the exchanger. The damper is the same as the rest, it only opens when the water temp goes below 170F. It does have a blower to force air under the fire to recover faster.

The constant circulation in the Central Boiler OWB loop is mainly for constant hot water convection heating. Also for instant demand heating in the house if the floor loop comes on and draws heat from the boiler loop line. Also easier to deal with and a lot less variation in water temp in the lines. Fewer controls that way, and less to go wrong over time. The OWB damper and floor pump are on separate control systems. The OWB water tank effectively includes the the water in the OWB to house PEX loop and HXs. There is some heat loss from the water running constantly in the lines, yes. Far more heat is lost from the radiant house heating going out the windows when it is cold. We have a large house with a lot of windows and vaulted ceilings, and a very open floor plan with few doors. When temps drop below 20 F here the wood demand doubles over freezing, and at 40 F the demand is about half of that when it is freezing. Above 40 and it does not burn much wood at all.

Here the ground does not freeze much more than an inch at most, and I have the OWB PEX lines buried about 18 inches. I also have the PEX lines wrapped in foam sleeves and then in a 4 inch corragated drain pipe. The main thing is to keep ground water from robbing heat from the lines; that is usually the biggest loss of heat in buried PEX lines. The drain pipe keeps ground water from coming in contact with the lines. In the attic where the lines come into the house I just have the lines wrapped in foam. I also have a bypass valve up there, and a set of air bleeder hose bibbs at the very top of the PEX loop in brass. I only had to bleed the lines once when I filled the system.

One other thing is about OWB sizing. Most OWBs are far larger than they need to be. One reason that we went with CB was that they had a smaller boiler available that better matched our heating needs. They now have an even smaller one that may have been better for us (and a little cheaper). But we have the capacity to expand the sytem to heat the hot tub or heat the garage when it is done. I want to put in a water to air HX in the ceiling off of the return line to the OWB and run a squerrel cage fan to take the chill off in the garage in winter. You can also add de-icing loops in concrete, heat outdoor patios with radiant heat (really nice in fall and spring) and do some other creative heating stuff with OWBs and hydronic heating.

Also there is the issue mentioned of corrosion. CB provides a good corrosion inhibitor to add to the boiler water that lasts for about 3 years under normal use. I have little to no rust in the firebox side of the boiler, and I do not know of any people that have had a problem with rust in a standard steel CB OWB. I do not even use Ashtrol, which is basically ag lime to keep the ashes from rusting the inside of the firebox. From my research on creosote, it has little corrosive effects on mild steel. I did not buy a stainless steel CB unit, though they offer them as an option. More money that you really do not need to spend, and stainless does not conduct heat as well as mild steel does. For that matter antifreeze is a poorer conductor of heat compared to plain water, and a reason that it is not commonly used in OWB water loops.

 

[highpower]

The Hardy has 50' copper coil that runs through the 110 gallon water tank on the heater. The water in the tank is 175F. The supply line is cut at the top of my water heater so when someone in the house turns on the hot water the cold water goes out to the heater (90') through the coil and comes back around 160F and goes into the water heater. No pump needed except my well pump of course.
I have a 3200 square foot house over a full basement with two central units. Both are turned off, except for the blower on the main unit.
The Hardy is not pretty. Looks almost like a big stainless refrigerator sitting out back. But looks are not everything. I bought a little larger unit than I need right now but the plan is to add another pump to heat a shop when it's built. I plan on a water to air exchanger with a fan. A thermostat will turn on the second pump and the fan.
It is amazing how many ways people can come up with to do the same job.