Managing creosote in CRS 7300E during shoulder season

[Rush River]

Hello Boilers,

Seeking advice from my elders

This is my first season with a new CRS 7300E Pristine gasifier. I am heating our new "shouse" , 2000sqft in living area, 1200sqft in garage, all on concrete slab with radiant in-floor and propane boiler for backup.

I followed all manufacturer reqs with break-in fires, proper filling, etc. However, I am already having challenges with creosote buildup, particularly on the rear air intake plate, and I have burned through 2 solenoids in first month of use due to increased resistance from the metal plate sticking shut with tar. I've got 5 cords of good dry wood from a bunch of standing dead trees so I know dry wood this not the issue. I talked with the manufacturer at CRS and they basically said that this is a common problem during shoulder season when temps get warm during the day, less heat is required, and the wood in the firebox is left to smolder for long periods of time leading to excess moisture and creosote. My house is also spray foamed, so I can understand that its not requiring a lot of heat when temps are in the 40s-50s. They reassured me that once temps get colder this won't be an issue.

I'm kinda bummed though that the boiler is going to be so difficult to use during shoulder season. Up here in Wisconsin we can definitely have long Autumns and Springs and I don't want to depend only on propane during these months. I've been nursing the boiler now with frequent small loads trying to achieve "dry burns" in between each load, I set the differential to 5 degrees (so hi temp 180, low temp 175) hoping for more frequent burns, and also just picked up a bunch of creosote removal sticks to add to the fire weekly per a woodboiler.com article I read.

I'm wondering if other more experienced boilers have any tips for managing a CRS gassifier during shoulder season (Oct-Dec, March-May). I knew the boiler was going to be high maintenance, but I didn't expect my system to be so delicate that a couple days of warm temps would derail the whole thing... any thoughts or ideas to make this go more smoothly.

Thanks in advance,
Learning to burn in Western WI

 

[Tonty]

To know where your wood moisture is, you really need to get a moisture tester to see how it tests out. Dead standing trees don’t dry near as fast as cut, split, stacked, covered wood. That would be a place to start. Gasifiers are happiest with wood moisture content less than 20%. I can burn wetter in my Switzer if it is hedge wood, but I don’t like to.
For most gasifier boilers to work well, they need water storage to act as a “battery” to store the heat. That way they can burn full bore, heat up the water “battery”, shut off, and then you can use the heat from the water “battery” as needed. Once the storage gets down low enough (not less than 120 perhaps), you do a burn again. This may be old news to you, but just so that has been stated.
I know that your boiler is probably an outside unit with some water storage built in so you may be able to make it work, but during the shoulder season you will most likely have some creosote build up if you don’t have storage.
For reference, my boiler has 600 gallons water storage, and I wouldn’t want any less than that.

 

[maple1]

What are the water return temps at the boiler inlet? Lots of potential for that to be too low, with slab heating, if not designed right.

 

[Rush River]

What are the water return temps at the boiler inlet? Lots of potential for that to be too low, with slab heating, if not designed right.

I'm not sure how to get an accurate read on boiler inlet temperature... would I have to wrap a thermometer sensor around the PEX pipe at the boiler return? I know that my system is set up with a mixing valve that combines cold return from in-floor pex with hot outlet from the braised plate heat exchanger so that temp reaching the floor is always 120. I'm not sure what the temp going back to boiler ends up being but I imagine it fluctuates depending on whether both my zones, house (kept at 68) and garage (kept at 58), are running. Is there an easier way to check?

 

[Tonty]

I use something like this, but mine is on copper.
https://www.supplyhouse.com/Winters-Instruments-TCT167-2-5-Aluminum-Clamp-On-Thermometer-30F-to-250F
You could also use an infrared thermometer, but those work best on dark surfaces.

 

[maple1]

I'm not sure how to get an accurate read on boiler inlet temperature... would I have to wrap a thermometer sensor around the PEX pipe at the boiler return? I know that my system is set up with a mixing valve that combines cold return from in-floor pex with hot outlet from the braised plate heat exchanger so that temp reaching the floor is always 120. I'm not sure what the temp going back to boiler ends up being but I imagine it fluctuates depending on whether both my zones, house (kept at 68) and garage (kept at 58), are running. Is there an easier way to check?

Yes. I've used a smoker thermometer under pipe insulation before. My boiler has temp guages T'd in at the boiler fittings. The generally accepted minimum return temperature to prevent excessive creosote condensation is 140°f. Your boiler should have a boiler protection loop plumbed in to keep it above that. Kind of does the same thing as your floor mixer - adds hot water from boiler outlet to the boiler return to keep above 140.

Edit: a few boilers have that built in. I don't know about yours.

Edit again: yours may be fine and that might not have anything to do with it. Gasifiers can pump out a lot of heat and if there is no place for it to go, the boiler will damper down and smolder.

 

[hobbyheater]

What is the BTU output of your boiler, how much water does it hold ,and how many BTU's does you house and garage pull in the shoulder season ?
These are 2 popular boiler protection valves , sounds like your boiler does not have either.

 

[brenndatomu]

Water storage takes the pain out of fall and spring...just charge your tank(s) back up whenever they need it...every few days if things are done right.

 

[hobbyheater]

There is no magic fix for your problem ! Most standing dead trees eventually rot so you are burning wet wood unless a moisture meter says otherwise ! No boiler protection valve makes more creosote . Setting your differential to just 5 degrees will never allow your boiler the time to gasify so again making more creosote .

 

[Unextinguished]

As mentioned by others, boiler return/inlet temperature is crucial, to keep it above 140. Not only does this reduce creosote, but, if your boiler return/inlet is running lower than that you may have sustained exhaust gas condensation in the boiler which will create corrosion that will shorten the life of the boiler.

Also as mentioned by others, thermal storage is helpful bordering on essential with a gasifier, especially for light heat loads and in 'shoulder season.'

In the short haul (before or without thermal storage), if you and your family are not phased by moderate temperature variations, you could "load" your concrete slab with BTUs during gasifier burns, so that your gasifier is running full throttle, sending heat into the slab from whatever batch of wood you have loaded into and burning in it - then the mass of your slab can 'coast' for a while until the next burn (and have the propane set to not kick in until something lower). It's a different way of thinking/ operating/ "lifestyling" than the usual modern assumption of a narrow band thermostat kicking a short cycling fossil fuel combustion appliance on and off in short sequences to maintain a dead-even constant temperature - but it's probably a lot more like humans were OK with up until pretty recent history.