Pacowy wrote:1. Use of DHW clobbers heat production from steam systems faster than hot water systems; a decent margin above the installed radiation is needed to prevent excessive interference, esp. with the "growing family".
Please explain this, how could it clobber the system more? I run steam and have no problem with my hot water, it barely makes the boiler kick on. Coal loves to burn hot. After using this for a few years on steam i think hot water baseboard or even colder radiant heat would not be making the best use of burning coal. See what LSFarm heats with a 260 and tell me this person should use a 260 also? So in the future when he gets windows and insulation, the 260 will be overkill. AA's spit out unburnt coal when they are oversized for the job. The AA130, as far as i know, will output more btu than a stock EFM 520. There is a rating on it for 540? I think that is a rating for the steam sizing. I would install a AA130 for now, maybe run a hand fired or rice burning stoker stove and after the windows and insulation, sell the stoker stove. He could also install a AA260 or EFM700 then sell that down the road for a smaller size.
2. To address the cold winter "feel" of old houses, many people run their coal boilers without jackets. This acts as additional radiation that heats the basement and first floor, but requires an additional boiler output margin to produce the same steam.
Try and find a AA with a jacket, won't happen. He can have a coal boiler hooked up to the steam for a few thousand dollars if he does it himself. You would have to ask the guys who refurb them but i bet a lot of them taken out of service are setup for steam. Steam and oil don't mix, steam and coal, yes.
3. The "growing family" might decide in the future to add radiation (in the attic, basement, etc) to create additional living space.
If you add to a steam system, good luck, you'll need it. If they rip it all out and go to hotwater, why not. But we often talk expense and if appears the steam is in place and working so why not just change to a coal boiler as is. They might also close off the attic and unused rooms upstairs. You can turn a steam radiator off and close the door to that room. That would lower your btu requirements? If it's an old house, guaranteed the basement will be cold, damp and home to spiders and whatever and most likely never be turned into living space. The coal boiler will warm the basement and warm the first floor floors, yes no doubt.
4. I'm not a boiler pro, but to the best of my knowledge up to a point there is an efficiency advantage associated with running a bigger boiler at less than full output vs. a smaller boiler flat out, at least if the bigger boiler has a larger heat exchange area (i.e., if you assume the same gross input for each).
I think you have that backwards. Running the boiler at close to max output should show a higher efficiency. Mine hardly runs now and it is smaller by 40,000 btu than the oil boiler it replaced. I could heat 2 houses with mine.
Overall, if somebody's going to put a bunch of $ into a coal-fired steam system, I believe they should take extra care to ensure it doesn't turn out to be underpowered.
I picked up my boiler for $1500, add maybe a few hundred dollars to refurb it, got it into the basement myself, removed the oil and hooked up to the steam myself. It works fine, i'm almost 50 and have never really done plumbing before i bought this house so it can be done for a few thousand $ and your free labor. If i had to move and bought another house, i would do it again myself. 100 year old house most likely had coal to start with, if in NEPA., He could purchase a refurb and have it installed by the same people for $4-5000 if the rest of the system was in decent working order. There was a thread on here with people telling how much they have heated with a EFM 520, some were a lot of square footage and outbuildings and such. I'm just thinking a 700 would be overkill. I like the idea of a 520 or 130, with a Stoker rice stove to supplement.
Done putting the chickens to sleep and eating a smoked chicken that was in the smoker for 6 hours, so please don't mind my posts, just bored.
1. You get steam when your boiler water gets to 212 deg and then absorbs the "latent heat of vaporization". If you add a DHW load when the boiler is trying to make steam, those btu's come pretty much entirely from steam production. Put another way, with a steam system, if the DHW load pushes your boiler water to 211 deg, you get 0 steam into your radiators. With a hot water system, even if the DHW load pushes down your boiler water temp, you'll still get some heat from your radiators.
2. My point is that any boiler, including an AA, if run without its original jacket basically can't make steam per its original specs. If they have any future scenario that would involve running a coal boiler without a jacket, they need to factor that in when they compare it to the performance they get from their current oil-fired boiler.
3. As far as I know it's not a big trick to add hydronic heating zones to a steam boiler (without converting the existing steam radiation to hot water) and several forum members have done so. My last house had a hydronic loop and my current house has an indirect water heater; both use water from steam boilers.
4. If you burn 20 lb/hr in a boiler with a given heat exchange area, and I burn 20 lb/hr in a boiler with, say, a 25% larger heat exchange area, all else equal I'm pretty sure more of my btu's are going to end up in the water. A given boiler may work most efficiently near its maximum output, but that doesn't tell you anything about how it compares to the efficiency of other boilers with larger hear exchange areas.
Of course, if you find you have an underpowered steam system you can always shut off radiators, manage the timing of your DHW consumption, insulate the boiler and live with cold floors, etc. To me, that misses half the point of the cheap btu's you get from coal - you can choose to have a quality of life that involves greater comfort in - and even expansion of - the habitable area of your home, as well as prodigious amounts of DHW, all while saving a large percentage of the cost. Especially with steam, I just don't see the point of cutting it too close on capacity.
P.S. Mozz, how many sf are you heating to what temperature, and what is your annual coal consumption? Thanks.