Stuck Selecting the Right Size Boiler

My new-found love of coal has progressed to the point where I'm trying to make a decision about a boiler to add to the home system. Stuck on selecting the right boiler. So, I have a few questions and hope I can get some guidance. Here's my situation:

I currently have a Weil McLean oil-fired boiler that I installed (hated the heat pumps) with basboard about 15 years ago. Works fine. I have three zones. House is 18 years old, about 2,400 sq ft. Open design, with big cathedral main room so lots of wasteful air space with three levels of pella windows. Insulation is pretty good. The boiler is a model 68. Tag says it is rated at 114,000 btu/hr. I use it to heat my domestic hot water, but I run this into an electric water heater. Actually have the water heater switched off. I figure I burn about 6 gal/day of oil. I also use a propane fireplace insert to get a little more heat in the main room during the evenings. All my utility gear (boiler, water heater, pump tanks and water conditoner) is in the crawl space. No room there for any more gear and it wouldn't be fun handling the coal and ashes if I had a new boiler down there.

My plan is to put a new wing on my barn, probably about 16 x 24. I'd put the boiler in there and coal storage. Run about 80 feet of insulated pipe underground and tie into the oil fired system so heat would switch to oil if we are away and the coal system is down. So, here's where I'm stuck and a few questions:

I like the AHS-130, but I got a pretty nice quote on a Harman VF3000. The AHS is probably more efficient, but I think they are both good boilers. And, the folks at AHS indicated they probably won't do much for "spring discounts" so I'm looking at a big enough price spread to tip things to the Harman. But, the BTU rating is 95,000. We did an audit when the oil system was installed, but that was long ago and I can't remember if we went with the boiler I have because it was about the smallest available at the time. So, I'm wondering--since coal is burning all the time (even at idle) do coal boilers work differently than oil, and should I be concerned that the Harman may be undersized? I know there will be some additional heat loss in the pipe between the barn and the house, but the specs indicate it won't be too bad.

The other question at this time is how much radiant heat should I expect the boiler to generate? Will it be enough to warm the boiler room? And, if so, will there be enough residual heat to provide some modest boost to the main barn area if I have a sizable opening into the barn? I have a standard garage door on the side of the barn where I would bump out for the addition. I have a stove in the main barn now. It would be real nice if the boiler added some heat when the garage door separating the main barn and addition is open. Of course, I could put another zone in the main barn area but then I think I Definitely would have to upsize the boiler (the barn is 30x40x12) and even the AHS 130 might be too small.

So, any thoughts?

steve

It sounds like the current heat system is already undersized. I wouldn't undersize the coal boiler... If you have a 114K boiler right now, and have to add additional heat with a propane firplace unit, then you really want to have more btus available.
The AHS unit is a very good boiler..it's 130K BTU rating is conservative.. and it can make that heat output day in and day out without the heat exchanger needing cleaning.. it's design is self cleaning..

You will not get a lot of radiant heat from either boiler.. If you want to add heat to the shop, you should install hot water piping in the concrete floor of the new addition and a 'Modine' water to air heater as well. This of course will consume more btus.

I'd not limit yourself with the smaller boiler.. go with enough 'extra ' BTU capacity that you can heat the addtion and the house to a comfortable level.

Greg L

You will lose some BTU's in the piping also, it sounds like the 130 would be perfect.

Most oil and gas fired furnaces and boilers are oversized. If you are heating 2,400 sq. ft. with 3 zones, that oil boiler should be much more than capable without having to suppplement it with the propane fireplace. I'm heating 4,000 sq. ft. with a Harman VF3K with no problem. My oil boiler never fires. I too have a domestic coil in the oil boiler dumping into an electric water heater. I do leave the electric water heater on but it only comes on to maintain temp, it never sees cold water. I don't know what the price tag is on the AHS130 but I'm guessing it's substantially more than the Harman. Talk to some of the other forum members who have the Harman before you decide. Oh, and I keep my water at 140 degrees too. This boiler has way more potential than I'm using.

Go with the AHS 130, you will be very pleased. To save some expense go with the standard grate timer. It will work fine and you can always add the thermocouple controller later. The PID controllers are available from non-name brand sources and are much cheaper than the Fuji AHS uses.

You can make a heat loss calculation to determine your actual need. The most accurate method is a HVAC standard called Manual J. It uses an Excel spreadsheet to make the calculations from insulation, window and door data you enter about your house. It's possible to do it yourself but it has a steep learning curve.

Based on your oil average oil consumption of 6 gallons per day--or about 840K BTU (gross) per day. I would expect that the Harman would be adequate for your current heating needs. The big unknown is the heating load that will be added by the barn. Putting the boiler in a cold barn will result in some significant amount of heat being lost there. If you actually use the coal boiler to heat the barn that could add significantly more load. An additional heat loss factor will be the 80 feet of underground pipe. The loss will depend on how effectively you insulate it.

The maximum output of a properly sized heating unit is typically used on only a few days per year and even on those days for typically a few hours. So even with a slightly undersized coal boiler you would be fine for 95%+ of the heating season heating only with oil. For those few days that more heat is required you could use the oil boiler for additional heat. You could even install controls that would make that automatic. Of course if you go that path to save money on the boiler you have to factor in the additional cost of the controls.

You asked: "I'm wondering--since coal is burning all the time (even at idle) do coal boilers work differently than oil,?" The short answer is no. Output ratings, typically BTU per hour, are based on firing for the full hour for an oil boiler and for the combustion air blower running for the full hour for a coal boiler. Therefore it is appropriate to compare BTU ratings.

Thanks all for your comments. Just to clarify. My existing oil boiler does a great job. It's just that I grew up a bit closer to the Canadian border, and my wife is from the eastern shore of Maryland. She gets this wild look in her eyes whenever a snowflake falls. The propane fireplace was a compromise. I get to keep the thermostat set no higher than 70 during the winter and she can use the fireplace during the evenings to get that heat boost she loves. She would be happy if it were 90 and 90 % humidity all year long. I find the mid-60s to be pretty comfortable and a bit lower is nice for sleeping. Her office is in the house so I suspect that when I switch over to coal she will crank the thermostat up and I'll be opening windows. Life was much simpler a few decades ago when I was single.

steve

i am heating a 2000 square foot ranch witha keystoker kaa-2 and works great.i am running 4 zones and making hot water. the only problem I have run into was 168degree water out of the kitchen sink. had to install a whole house tempering valve did not want to cook the kids in the tub. keystoker seems to make a high quality stove for the price I am very happy with my unit plus I only burn a bag a day alot cheaper than oil

1975gt750 wrote:i am heating a 2000 square foot ranch witha keystoker kaa-2 and works great.i am running 4 zones and making hot water. the only problem I have run into was 168degree water out of the kitchen sink. had to install a whole house tempering valve did not want to cook the kids in the tub. keystoker seems to make a high quality stove for the price I am very happy with my unit plus I only burn a bag a day alot cheaper than oil

WOW 1 40 lbs bag a day is AWESOME! Everytime, I read that in a post I cry a little.hehe

What do you keep your t-stat set at?

keep the t-stat at 68 during the day and 60 at night. I use programable t-stats

If I were to be selecting a boiler for the above application, I'd consider a refurbed EFM boiler... They are very well built, and parts are available. The output is very adjustable, so you can set it for the application..

If you plan on using the garage heat very much, don't undersize... The AHS, EFM can be cranced up to greater output levels if needed.. But the Keystoker and Harman boilers, once you are pushing hot coals off the end of the grate, it is maxed out...

How about a used AxemanAnderson 130?? you can make a big hopper as part of your new construction, make it loadable with a front-end loader from outside if you want, and even get creative with ash handling if you want, A very good used or refurbed AA is $1500-3000, or a rebuildable one for $1000-1500. I'm very happy with my AA260 that I rebuilt.

As for sizing the boiler::

It's all about BTU load... a 2000sqft ranch with good windows, good insulation, and a fairly tight construction [house wraped, well caulked] will not need much heat, especially with the low thermostat settings.

You have to compare apples to apples.. I think my place compares closely to member 'e.alleg' . I'm delighted to be burning only 3 tons a month when every week I have -0* nights and teens and 20's days... and I'm heating a 4100sqft old drafty house and a 2400sqft polebarn shop...
If I could heat only half the house, and insulate it to modern standards, I'd be down to about a ton a month, that's 250# per week, so 75-80# per day... but it will never happen... maybe when the temps are high 30's at night and 40's in the day.
I keep the shop floor at 50-60*, the majority of the house at 62* and the 'TV-computer room' at 70* when occupied . I would be spending 2400-2800 PER MONTH for propane to heat to the same temps...