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Posted by John Anderson on April 30, 2008 at 03:00:17:
Hope this is an alright place to post this. First this is in a 4000+ sq ft LOG house in Palmer AK. Need to replace the 20 year old Burnham boat anchor (that has been run by previous owner with standing pilot, year round set at 180F temp even though we don't currently have indirect DHW) for a couple of reasons; mostly for age and peace of mind but also as the roof needs replaced and the current vertical vent pierces it in two locations and I'd like to direct vent out the side of the garage where the boiler is instead. If I could cut down the $450 a month gas bill in the winter, that would be nice as well of course... Also the house came with a new in the box uninstalled Amtrol Boilermate classic (not my first choice but here and free) and the existing atmospheric WH is of course 20+ years old as well.
I used to be a mechanical engineer but have been doing something else about the last 10 years. I did do design of commercial steam systems 15 years ago, but although I've installed a few hydronic systems with my contractor uncle 20 years ago, they were all the same as what is in this house now.
Some specifics on the house, first and most confusingly for heat loss calcs is that it is 9" log wall upstairs, pressure treated wood with (I think) 3.5" fiberglass in the foundation walls, and roof is 5-6" fiberglass over 2" toungue and groove wood. Using the slant fin software and in my thought being VERY conservative and assuming the worst I get a load of about 95,000 for the house proper and another 30,000 for an entirely unisulated 800 sqf garage. Currently the house has 150ft of baseboard for about 75000 or so of available emitter so I figure the loss I calculate isn't too unreasonable, should be accurate to conservative. The garage has a 25000 output Modine space heater (which can not keep that space over 60F on coldest days.) Currently the house is in 4 zones with Honeywell valves, and an actually beautifully laid out and plumbed system which I'd hate to scrap entirely. The garage is a 5th zone that the previous owner was going to remove and install the boilermate instead and apparently lose use of the garage in the winter excepting for what heat the Burnham dumps into it by its very mass and presence. The current system short cycles ruthlessly most of the fall and spring, and undoubtedly from what I gather from local contractors and reading here an outdoor reset would probably net me impressive gains in and of itself, but I do have concern for how cool I could run the return anyway (particularly with a cast iron boiler.) A separate issue is the great room (800 sqf with 20 foot ceiling with 50ft of baseboard connected to a loft area of another 600 sqf with currenty NO emitters) emitter is JUST sufficient and no easy way to install more. On a -10 to -20 day all is OK actually, can heat the room to 75F if I wanted, but the 30 year old andersen windows, even with tight storms, leak severly when the wind picks up, and I'm talking 60-70mph average hitting 2 sides of this room for weeks at a time in the dead of winter, when combined with even a 0 or below temp on a windy day the current 50 feet of baseboard can't keep the room 65F. I will replace the worst offending windows as well, but anyway you get the idea that I figure my loss calcs are about accurate as on an average "design day" without wind, things seem to work out reasonably evenly.
Now this is the kicker of course, the current boat anchor is 230000 in with an I=B=R of 170000. Do I believe my calculations or not is my first question? Next thing, several (most) contractors up here reccomend believe it or not a regular atmospheric boiler with an added outdoor reset, like even a Burnham Series 2 or W-M CGa!!! I figure although I do not trust the technology of mod/cons (I'm a sort of young old fart, plus with high temp baseboard I doubt truely if a mod/con will really net much more than 90 anyway during the worst of the winter) at least I should go with one of the units mentioned in the subject line. The Revolution seems to have a bad rep up here, injector reliability issues I am told. The GV seems to fall into the same boat, a bit too much technology for a non mod/con, some like it some say "I'd never have one in my house." Is the CGs a reasonable choice for me, the largest size is an I=B=R of 122000, if truly my load is more close to my available radiation will that be enough with the Boilermate? That current anchor does not come anywhere near running continuously even when the emitters can't maintain the the garage and great room at temp.
A total but realistic aside is that my wife (a doctorate educated smart lady) given a reasonable explanation of things thinks we should still just have a standing pilot atmospheric for "reliability." That I can't stomach but I don't want to be calling anyone in the middle of the night to service anything I can't figure out myself. Thoughts, opinions, suggestions?
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