That all sounds right on course to me! I watch primarily the supply temp in the house, since the tank temp is outside, to determine when to fire. But I never fire unless the tank temp is down about 120. One thing I will do, I have all radiant, is drain the heat out of the Garn until the supply is about 115 or so....then fire. I've also come to crank up the thermostat temp while I am burning, if it is cold outside, to "supercharge" the enormous concrete slab. The floor will get up to about 83F or so, it feels incredible when it is 0F outside, and the air temp about 74-75. We have a lot of glass and when the temp is that cold outside, it is great. I won't call for more heat then until 12 hours or so later, setting tstat back to 72. I use this really only when it is very cold outside, less than 20F.
I heat DHW as well, which is the really what determines when we fire. I set my controller (sensor in the indirect and system controlled by Tekmar 363 is it?) for DHW at 115. So I can reach that point when the supply is 120 or above. Sometimes (like this evening) the DHW will run for hours if the supply is at 119, the indirect at 118, as it turns off when it reaches set point plus 4. So quite seriously, the need for DHW will drive when I fire. I can heat just fine down to 100-110 on the supply. I have considered some kind of DHW "supplement" which would kick in when the supply is below 120, just to get that much more heat from a single fire, and burn a little less wood. Though we only burn about 6 cord a year....2500 sqft, lots of glass, all radiant. When the addition comes online (another 1000 sqft) and if ever I connect the big garage/shop (2200 sqft), all radiant slab, then my load will increase a bit.
I also am still running my initial "non ideal" buried lines for part of the underground and I know I am losing there. Long story....short version is when I built the house in 2001 I placed the oil boiler outside in its own shed and brought the hot water undeerground via 1" hepex wrapped with foam "pipe insulation" inside a 4" conduit. I am STILL losing here for sure. One of these days I have to connect the addition (still unfinished....the eternally DIYer here) to the system and will use the new 1.25" microflex buried lines. I think that will save me considerably, perhaps as much as the load on the addition.
One thing I notice is that my high temp (the 180's right after firing) don't last very long. Within a couple of hours I am down to the 150's. I think that is the crappy buried lines. But once I hit the low 150's it will persist for quite a long time. Once I get down to the 120's....I have many hours left. Higher temp differential, bigger loss. For all I know my 4" conduit could be filled with water.
I wouldn't fire with anything more than 145 or so, but I also don't need the higher temps. With the baseboard or air-water HX, and the need for higher temps, I suspect you'd have to burn sooner. I know I always recommend the Garn for radiant but tend to dis-recommend for air HX or baseboard unless the coil or lengths of baseboard is massively over designed to work with lower temps. It just seems to me that the system wouldn't last very long (i.e. not one fire a day) if I had to have 140 minimum water temp. At that point, to me, one of the other boilers with storage would be likely better....I have the perception you keep those fires going longer. More frequent feeding the monster, but more consistently higher temps.
The only place I have seen water creepage from the flue is the coverplates just below the draft motor, and only on the first fire from 70F tank or so. After that, not again. I did put silicon around the chimney on the rear....I believed I DID screw the insulated flue onto the flange on the rear BEFORE I built the box around the unit. I boxed off around the pipe to hold back all the fiberglass. Yes, it will be a pain to get access to the screws if I need to remove.
You can really tell when you need to clean your flue tubes by looking at the exhaust temps. Generally the flue temp will be right around 500, just a touch higher. But as time goes on, it will begin to creep up. Time to clean. When I cleaned this late fall, I was getting up to about 600F at the flue, as it had been about 14 months or so since I cleaned. After cleaning, it dropped right back down to the 480-500 range. I just use the brush and rods and spend about 15 minutes scrubbing each of the 4 lines. I got a fair amount of soot out....maybe 4 cups total. I shouldn't let it go so long, but was busy hanging log siding all summer.
We do burn all year round for DHW. In the summer, I fire about once every 4-5 days. Household of 5, at least 7 showers a day, two loads of laundry, etc. I will try and burn "crappy" wood then if I can, i.e. pine I drag in or similar. "Free" DHW heat.
Puffing issues will be had when you use smaller splits, or lots of lumber scraps, or say a pile of white pine log siding scraps! It is quite an event when it happens, as I swear it feels like the door is going to blow open. In fact, with my too large of a load of log siding scraps, I actually had a little puffing out of the left bottom flue cover, after I cleaned it out. Tightened the nuts a little more...no more. I have only seen puffing a few times though....literally 3 or 4 since 2010. Each time I knew it was likely to happen. SO just think about what you are putting in the beast.
Regarding the firebrick in front of the air supply. What I have noticed is that to get a clean burn, i.e. no smoke visible coming out the flue, I need to place something here to deflect some air upwards so that all the O2 isn't consumed in the firebox itself. My wood is just under 24", limited by my splitter stroke length, so I try and build the fire aways back intot he chamber. Then after it is going, say a few minutes into the burn when I am sure it is cranking, I will place a small chunck in front of the stack. This really seems to clean up the burn every time. I usually use those small end pieces that one always has laying around. I did cut some "cookies" before about 2-3" thick when broken in half make an ideal piece for this. They burn up of course, and I don't have to remember to pull the brick out, or not bury it, or drop wood on it, etc.
One last tidbit. I have the sensor that the controller uses in a well and also another sensor in another controller in another well. These two sensors will be about 10F off from each other! I suspct it has to do with the contact of the sensor in the well....I am willing to bet one has grease and one not...etc....but i haven't really ever looked into it. One of these days, one of the projects is to install the 32 one-wire temp sensors every where and watch what is going on. But that will only want to make me build a system controller that I can finely tune everything! I like the Tekmars, but I sure wish I could variable speed all my pumps to only bring in exactly what I need from othe Garn, get rid of some time delays it appears to have, etc.
All in all, we are very pleased. I run through about 2 Mg rods a year. Don't understand why this is since the water chemistry has been great. Make sure you send out samples every six months to Mike at Precision. Since 2010, I only had to put in one bucket of stuff, about $80 or so, plus a rod every six months! They do add up from Dectra. Must be an electrolsys issue, but I have my pipes grounded, not sure what more I can do.
It is quite amazing how clear the water stays inside the Garn. Take some time and inspect it when you get your sample every six months. I have yet to see anything that I think is a problem. The flues and firebox will get a white scale on them, presumably from the additives, but this is normal. After my first flue cleaning and I looked inside, some of the scale had broken off and was floating on the surface. That's the only thing I have seen besides clear water in this thing.
As long as there are no corrosion issues, I assume this thing will last a very long time. Rick's issues (linked to above in another post) were related to bacteria. On a chicken farm, I can imagine this is much more likely than in a homeowner environment. I would be really bumming if that happened....but Rick has also stated that he feels like it was his fault for not sampling water directly from the Garn itself. Hopefully things will continue smoothly.
For us, with radiant, I don't think there's a better way. I only wish I had sprung for the 2000 instead of the 1500....but it is rather rare that I fire more often than 24 hours anyways....so not a real issue at all. I do think the numbers are a little more efficient. Must get the final exhaust temp a little lower since there is more surface area in the longer flue length (I am assuming) in the extra 500 gallon volume.
OK, exhausts my Garn learning tidbits. It's been bulletproof operationally....I don't think it could possibly be easier.
One more....I find that when I put the manhole cover back on, the gasket there will fall apart after just a few opening/closing. I only look inside once every six months, but I essentially plan to replace the gasket every 12-18 months. I have done it once...I need to do it now I think. If you get a little opening, you will get some steam release, and your water level will drop accordingly. Takes some time...but it will happen. I took off the old one, used a hand grinder and sand paper to clean up the lid, and put on the new one. Tight as can be. Just something else to think about.
There WILL be some "sparks" and little chunks blowing out the exhaust at the rear....so keep this in mind. Don't let the grass turn brown and dry where the exhaust goes. Another member here with the vertical chimney has some concerns with embers blowing up and out....not sure what his final outcome was. But if you sit outside and watch during a night burn, you will see them fly out. The 90 into the garbage can likely will solve that issue totally as well. My 90 usually falls off and I vent outwards....oh what a screw can do here, eh?
Way too long. Enjoy! I remember my excitement/apprehension when I was looking to buy/did the installation. Couldn't be happier at this point....our fourth heating season. Not a drop of oil since Nov 17, 2010!
![[Hearth.com] Garn is up and running](/talk/data/attachments/122/122869-e54a43f2791c7893fdfa6d6285a0e7f5.jpg?hash=mU19b_dbDD)
![[Hearth.com] Garn is up and running](/talk/data/attachments/122/122870-e32de65e6ba9b7b45d07f961c9eb7833.jpg?hash=zdeN9go03e)
