How should I burn my non gasser boiler for max efficiency?

[Drewby]

Hello folks my name is Drew. This is my first post but I’ve been reading here a lot lately.
I am new to wood heat but not construction.

I just built a big house/shop combo to live in and its very well insulated with two furnaces and now a big Royall 6250 non gasser inside boiler. It’s about 250,000 btus. It will be heating a 5600 sq ft insulated slab and about 4000 square ft above it with radiators. I am going to use it to provide the bulk of the heating needs (hopefully)
My question is on the operation of this unit. I don’t have heat storage other than the slab. I was wondering what the expected MAX efficiency of this unit could reach if I only burn it fast and hot until the fire was pretty much out. I don’t want to have much creosote or waste the fuel so I wasn’t going to let it idle at all.
I’m going to pretty much run it like a Gasser in that respect.

Does anybody think it will reach 70%+ (on dry wood) if it’s run hard until it runs out of fuel?

Currently my plan is to just load it with the approximate amount of wood that I want to burn and start the unit and let the heat get pumped out all into the slab. No thermostat at all. Just my eye for the wood load and 300,000 lbs of concrete.
My propane furnaces will pick up the difference (or the windows) if I’m getting out of the comfort zone temp wise. I also have the concrete zoned to adjust the heat distribution as needed.
Does anybody run one this way to eliminate the idling?

These units will REALLY smoke if choked out and also waste a lot of wood.

Many thanks in advance!

 

[jebatty]

I just built a big house/shop combo to live in and its very well insulated with two furnaces and now a big Royall 6250 non gasser inside boiler. It’s about 250,000 btus. It will be heating a 5600 sq ft insulated slab and about 4000 square ft above it with radiators. I am going to use it to provide the bulk of the heating needs (hopefully)

What was your reason in new construction to select a non-gasser? I know nothing about the Royall, so no comment on possible efficiency. Seems like the efficiency question might have been better asked before deciding to install a non-gasser.

 

[Drewby]

What was your reason in new construction to select a non-gasser? I know nothing about the Royall, so no comment on possible efficiency. Seems like the efficiency question might have been better asked before deciding to install a non-gasser.

I got a very good deal on a used late model unit. It will be installed and in service until I can afford the Garn that I was planing to get, however if I get it to work real good then I might keep it around for longer.
I’ve heard stories about these smoke dragons getting choked into 30%-40% efficiency. I’m trying to avoid that by getting full, hot burns one batch at a time.

I’ll admit that most gassifiers seem like they will have trouble holding up for many years (20-30) due to there operational complexity. That never interested me about them compared to the more simple units like the Royall.
I guess time will tell lol.

 

[Fred61]

Burning "flat out" is the most efficient only if the boiler is engineered to extract the heat before it goes up the stack.

he other problem is that concrete does not absorb nor release heat at the rates needed to achieve your goal. You will probably overheat and destroy your pex in the process.

 

[maple1]

The only thing you can really try is to load the firebox for the heat load. That will take some trial & error. And maybe frequent small loadings.

Did some looking - that looks like a standard water jacketted boiler with no heat exchanger & more or less a straight exit from the firebox to the flue. Hugely inefficient. I used to have a small one constructed with same principals. I wouldn't expect it to be any more than 30-40% efficient. Less with sub-optimal wood. Adding storage so it can batch burn flat out might help combustion efficiency, but without good heat exchanging (example: tubes) most of the heat will go up the chimney.

 

[JRHAWK9]

Royall is made about 5 minutes from where I'm at here at work in Reedsburg, WI.

70% is a pipe dream with those OWB's. There are some EPA burners which can't make 70%.

 

[salecker]

If it was me...
I would sell the smoke dragon before i spent any time or wood on it.
Find a way to buy the Garn,don't spend any money on the one you have hooking it up.Sell your extra_____ to fund the Garn.
The square footage and no storage will keep you a slave to the firebox,unless you are OK with your propane bills getting high.
There is never money to do the job right. But there is always money to do the job twice.

 

[E Yoder]

I would agree you probably can't burn wide open and dump it into the slab, I don't think it could absorb it that fast. If it did it would likely overshoot room temp because you couldn't stop the radiation.
It would be worth talking to the folks at the factory about how to set it up. I'm guessing they expect it to cycle?
I've sat through some lab tests on non-gassers and continuous burn v. cycling didn't change it much over 5%. Loading lightly helped a lot though. Basically gave room for some heat exchange and room to burn off at least some of the gasses in the firebox.
Running without a thermostat will definitely be tricky, especially with the radiators, they'll begin emitting heat quickly.
Adjusting your loading to the weather definitely will help efficiency but it won't get anywhere near 70%.

 

[Drewby]

I've sat through some lab tests on non-gassers and continuous burn v. cycling didn't change it much over 5%. Loading lightly helped a lot though. Basically gave room for some heat exchange and room to burn off at least some of the gasses in the firebox.

I am hoping the full burn temps will get a little more effiecent then trying to slow it down.
I just can’t imagine 70% of the heat going out that little exhaust flue and only 30% getting absorbed by the water jacket. It seems like it would be at least the other way around.

As far as the slab taking all the heat at once I’m still not sure how fast a half batch of wood burns? Anybody have a guess?

This slab has over 5000’ of pet tubing and weighs close to 300,000lbs. I’m pretty sure the boiler won’t overheat it too fast. It would take probably close to 20-30 hours of constant burning to raise it just 10 degrees IMO

I do agree that smaller batches would definitely increase the efficiency of the unit though.

 

[maple1]

The engine in a boiler is the draft. That has the natural effect of carrying stuff (heat) right thru it and out the chimney if there is not enough heat transfer ability. Which there isn't in an ordinary simple water jacket boiler like that.

When I was running mine, I had to damper the pipe down to try to keep heat in the firebox long enough for it to transfer to the waterjacket. I would close it until smoke just started coming out the draft door then open it back up a tad. With the damper opened, sure it burned hotter, but the heat went straight up the pipe and the fire was burned out in like 3 hours. Then of course dampering it down made more creosote, which meant cleaning the chimney way too often (at least 3 times a year, usually 4) and constant coal buildup. It was a vicious circle that I was a slave to for 17 years. Some glad those years are over. It never had any published efficiency numbers but comparing wood used now with wood used then & the numbers for my current boiler, I am pretty sure it was in the area of 40%.

Was there any design work done on the system? You should have a BTU/hr number for it if so. How well is the slab insulated? You want to be careful sending hot water to it - others who have it can chime in, but I don't think it wants to be over 120 or so. You could also use the building itself as storage, sort of, if you don't mind some temp swings inside. Heat it a couple degrees or so warmer when the fire is honking then let it coast down a bit when it's not. But you would need lots of emitting horsepower for the recovery period.

 

[Drewby]

The engine in a boiler is the draft. That has the natural effect of carrying stuff (heat) right thru it and out the chimney if there is not enough heat transfer ability. Which there isn't in an ordinary simple water jacket boiler like that.

When I was running mine, I had to damper the pipe down to try to keep heat in the firebox long enough for it to transfer to the waterjacket. I would close it until smoke just started coming out the draft door then open it back up a tad. With the damper opened, sure it burned hotter, but the heat went straight up the pipe and the fire was burned out in like 3 hours. Then of course dampering it down made more creosote, which meant cleaning the chimney way too often (at least 3 times a year, usually 4) and constant coal buildup. It was a vicious circle that I was a slave to for 17 years. Some glad those years are over. It never had any published efficiency numbers but comparing wood used now with wood used then & the numbers for my current boiler, I am pretty sure it was in the area of 40%.

Was there any design work done on the system? You should have a BTU/hr number for it if so. How well is the slab insulated? You want to be careful sending hot water to it - others who have it can chime in, but I don't think it wants to be over 120 or so. You could also use the building itself as storage, sort of, if you don't mind some temp swings inside. Heat it a couple degrees or so warmer when the fire is honking then let it coast down a bit when it's not. But you would need lots of emitting horsepower for the recovery period.

There was no design work done to it. It should need about 180,000 btus an hour for a 70 degree heat rise though (the coldest days)
The slab has got 2” foam under it.
I just want to make it a simple and temporary system with the furnaces to pull the slack if needed.
I am only trying to get the most efficient burn out of a $1200 boiler.
The garn that I want is gonna be around $40,000 for the unit and it’s shed to be in.
For now if this Royall 6250 can get me some decent heat I would be happy.
I just can’t see that in the best case scenario that 70%-60% of the heat still goes up the flue.

FWIW I cannot pencil out ANY system....NOT A ONE except this $1200, great condition boiler to be cheaper in the long run then the $1.00 a gallon propane that I’ve had for years now. These new systems don’t even pencil out today if the wood is free and the time to make it is not valued at all.
Now if propane goes to $2.50 a gallon that’s a different story.

 

[E Yoder]

The efficiency is say more like 30-40% because it's an incomplete burn plus a hot exhaust. Two factors. Losing available btu's in smoke and then in not recovering heat.
I'm not criticizing your unit, but it doesn't match a modern gasser in efficiency.

 

[Fred61]

I suspect you'll get tired of feeding your "campfire in a box" early on, plus you may pause when your exhaust pipe glows red.

 

[maple1]

$40,000 for a Garn plus shed? There would be more economical ways to go that would still perform just as well. There are also some fundamental differences between that and your Royall (open & outdoors/shed vs. pressurized & indoors), that it would seem would make doing a swap a bit more challenging. You should be able to find a good gasser that would fit into your Royall footprint and set up some storage tanks somewhere in all that space. My 660 gallons only takes up about a 3.5' x 10' footprint. Although I would really like more, that's all the room I could make happen in my basement. But I also have my entire winters wood in there with it.

 

[Drewby]

$40,000 for a Garn plus shed? There would be more economical ways to go that would still perform just as well. There are also some fundamental differences between that and your Royall (open & outdoors/shed vs. pressurized & indoors), that it would seem would make doing a swap a bit more challenging. You should be able to find a good gasser that would fit into your Royall footprint and set up some storage tanks somewhere in all that space. My 660 gallons only takes up about a 3.5' x 10' footprint. Although I would really like more, that's all the room I could make happen in my basement. But I also have my entire winters wood in there with it.

The garn and all its part will run about $20,000. And then the shed that will attach to my house for it and the wood is another $15k-$20k. That will be real nice to have!

What is the going rate for a good gases with water storage? It seemed like they were around $10k-$15k??
Do I need water storage with a slab? I probably don’t need to have DHW or feed and furnace coils right now.

My thoughts were to try to get the Royal to burn as effectively as possible and not smolder it. It seems like small-medium batches would work fine and let the slab take all the heat and then the furnaces would supplement as needed the even it out.
I just never thought that 40% would be the max btus that I would get out of the wood I feed it...that sucks!

 

[JRHAWK9]

One issue is the water jacket will not allow for proper combustion as it won't allow for the temps required for complete combustion. The water jacket essentially quenches the fire leading to smoke (unburned fuel) and creosote.

 

[maple1]

Yes, a conventional boiler is essentially a burner with a liquid cooled fire.

Not sure about 'going rate'. A big part of it would be what you can source for storage. I got all my storage tanks for under $1k, from a big scrapyard that had a mountain of used LP tanks. I haven't priced boilers for a couple few years, but you used to be able to get a really good capable one for under $10k. My whole setup was right around $15k, but that is Canadian dollars with around $2k of currency conversion, freight & customs/brokerage. Plus 15% tax on all the stuff I bought here.

I think there is a used Eko 60 for sale down the page a bit here, and maybe other stuff in the classified section, but I haven't been in there for a long time.

And I would consider storage an essential for any boiler that has good heat transfer efficiency, slab or not. It makes a huge difference.

 

[salecker]

Your slab is not a heat storage unit.
Water is the best medium for storing and extracting BTU's.
I have never cleaned my chimney in 8 yrs of heating.
My boiler is a purpose built gasifier and it still dosn't extract all the btu's before they are lost out the chimney.

 

[Fred61]

The non scientific definition explanation for efficiency here is: "Make heat no faster than the surrounding water jacket can absorb it."

 

[E Yoder]

But- regardless of efficiency, storage discussion- you will need to mix the water temp down going into the slab. Probably below 120 F to protect the concrete.
I would at minimum also put the rads on a thermostat, with the low mass compared to the mass of the slab I see the potential for some big temp differences between upstairs and downstairs when you fire up.

 

[Drewby]

All good advice guys.
Thanks a lot.
I’m still not sure why the slab can’t serve as a heat dump during the burning cycles of any boiler. I know the room temps will go up and down some but it’s just for a shop at this point. I still have propane for a quick heat bump if I need it in the living quarters.
I also had know idea that the non gasser wood burners were so grossly inefficient. My unit is only 6 years old. I would have to believe that a boiler would be more effiecent at capturing the heat than a forced air furnace or any old style wood stove though. My other option was to throw an old Yukon wood furnace that I have in this bldg and just blow the air out the side into the big area and let the propane units do the rest.

I pretty much spent all my money on this new house/shop and am just trying to get the most out of my budget for now. My goal is to get a Garn as soon as I get the money saved up.

 

[maple1]

Furnaces & stoves don't have liquid cooled fireboxes. Which impacts the burn. That would be the main conundrum.

 

[jebatty]

Most literature I have seen states that water temp entering a slab should be between 85-125F, with a target being about 5F above desired room temperature. A wood boiler will be heating water up to about 190F, with 160F+ being very normal output during a burn. Therefore, using a slab as a heat dump for a boiler at high burn rate is a poor decision both practically and probably also from a safety perspective. Heat causes expansion and contraction, and excessively high hot water into a concrete slab may result in cracking and other failures in the concrete.

Using a mixing valve to temper down the water temp entering the slab is pretty normal practice. In my own case, the mixing valve is set to 100F water temp entering the slab, even though boiler output may be up to 190F. The consequence is that boiler return water temperature also then is very high, which means continuing a high burn rate will result in a need to idle or throttle the boiler to prevent overheating and boiling of the boiler water.

The heat content of the boiler water needs to go somewhere, and it can't all go into the concrete without potentially serious problems.This is where storage is needed to absorb the extra heat to allow the boiler to continue at a high and efficient burn rate. The water jacket in your Royall is not sufficiently large nor designed to serve as a heat storage medium. In fact a water jacket boiler, without a design like that used in a Garn, is inherently inefficient and must be idled repeatedly, or operated a low burn rate, to avoid over heating. Both of these burn methods are inefficient and are likely to result in large amount of creosote formation in the boiler, and from that another set of very undesirable problems must be dealt with.

I don't see any satisfactory result from how you wish to use the Royall, and if you proceed as you planned, all I see are practical and safety problems.

 

[CountryBoy19]

All good advice guys.
Thanks a lot.
I’m still not sure why the slab can’t serve as a heat dump during the burning cycles of any boiler.

It can be used as a heat buffer to a certain extent. Others have already given the limitations (maximum temp of the concrete etc).

The reason that it doesn't make an effective "bank" for storing heat is that it has a massive surface area that nearly immediately dumps it's heat back out into the air. Yes, the concrete will act as a bit of a "buffer" but it's not a bank. A bank would be a centralized storage medium that somehow restricts the energy being emitted into the space around it. The concrete floor has no way to restrict this.

Do you have carpet or wood floors on the concrete anywhere? Those things can act as marginal insulators to hold more heat in the concrete but they're still only marginal. Without some sort of insulator your concrete will lose the heat to the room almost as fast as it gets it from the water.

The heat capacity of concrete is ~ 0.2 BTU/lb/deg F... so when you start getting a bit chilly your concrete is still ~75 give or take a bit. The MAX you want to get your concrete to is probably about 85 (or maybe 90) to keep the air-temp comfortable. So you're talking about being able to "store" about 2 BTU/lb of concrete, or 600,000 BTU. If you're burning Oak that means your load of wood should be around 7 cubic feet assuming ~40% efficiency.

I don't think anybody is trying to say that you can't dump the heat to the concrete. They're just saying don't expect it to act as an actual heat bank that will hold you through the night etc because it doesn't really work that way.

 

[peakbagger]

Back in the seventies and eighties lot of "solar" homes were built with big rock filled storage areas, few if any really worked and expect most are abandoned. Up in New England the rock of choice was granite or concrete made with granite aggregate. Unfortunately both typically contain radon and the rock bed storage units become persistent indoor radon sources so the homeowner ends up having a heating system that doesn't work and the need for a radon mitigation system to boot.

I tried to run a non gasser boiler without storage for a couple of years. it was good to heat up the house when I was away in cold weather and the house was set at 55 degrees and occasionally some evenings when the outdoor temps were quite cold. The boiler circulated the heat so the house warmed up quicker as I had baseboard. My woodstove is in the basement so it took much longer to heat the entire house up but once warmed up I would use the wood stove instead of the boiler. I did save some wood with the boiler but once I put in storage tank I cut my wood usage by a third. That and a one ton minisplit run off of solar and I havent bought heating oil for four years in a pretty severe climate zone. My wood usage is in the 3 to 4 cord range.