BTU requirements ugggghhhhh!!! how to figure??

[bassman]

I have a outdoor boiler and it must go!!
so in my search of a new system i am looking at a multi fuel unit that can burn coal wood and waste oil all of wich i can get for almost free or in the case of coal for about $40 a ton.
as you know most boiler units ask for a btu requirement when selecting a unit and this has me stumped.
what i do know is that my greenhouse has a 20x22 exchanger with a furnace fan behind it and at night it will run almost all night straight .
my house has the same exchanger mounted in the furnace and it will run for about 15 minutes every hour on average.
my shop has another 20 x22 and it will run for 15 minutes every hour also .
they are all 100 000 btu exchangers so if i had all 3 running at the same time for 1 hour would that then mean i need 300 000 btus an hour??

 

[drmiller100]

i get 150,000 btus, on average.

doesn't leave any margin though.

 

[windthrown]

Sizing needs

We have a 250,000 BTU boiler for the house here. Smaller unit, easilly keeps up with the demand of hot water and space heating with hydronic floor heating. I sized it 2x the estimated heating demand for size and space of house and hot water demand, and allowed for expansion for winter greenhouse, hottub, whatever.

Several ways to size it. One is to look on a site like Central Boiler (they have multi-fuel units, and wood boilers and a good size/use/space BTU estimater there on the web: www.centralboiler.com). Another method to estimate is to look at what you are replacing in terms of BTUs. As a second estimate here, I sized our OWB unit based on the hot water BTU demand and the electric floor heater BTU rating that we replaced with the OWB.

Oddly, I got the same result suing both methods. Size/space estimate, and BTU replacement, and doubled the value for sizing the OWB. Bigger is not always better in this case. We could have gotten away with a smaller unit, but they did not make a smaller unit when we bought ours. The rating of the exchangers is not a great way to estimate the heat requirements. But there in Canada with your multi-heating demand I would suspect that 300,000 BTUs would be the minimum needed.

 

[windthrown]

Btw...

What kind of OWB are you dumping? Just curious.

We have all the free wood here that we could burn in a lifetime, so efficiency is not a big issue with us and the boiler. 5 cords a year on average, in exchange for $250-300 a month saved in heating bills 8 months a year. Also coal is not readilly available here. $40 a ton CDN seems really cheap. My brother bought a 100 lb sack of anthrosyte coal from a guy when we lived in California about 20 years ago and we tried burning it in our fireplace. It melted the iron log grate. Burning rocks still seems weird to me. I have lived on the west coast my whole life, and burning coal is very uncommon here.

 

[bassman]

What kind of OWB are you dumping? Just curious.

.

It is a cozyburn 250.
I am trying right now at 3 am to keep the water temp up.
I am loading in 8 inch pieces of scrap 2x4 and other pallet pieces along with used cooking oil and a stihl leaf blower .
my greenhouse is full of plants tottaling just over 6 grand so if they get cold they die.
winter hit hard again with alot of snow and wind.
but when my wife is selling plants and has a smile it is all worth it.
total crap for me so i will be buying a better unit.
.

shayne

 

[Husky137]

The issue may be your fuel source as opposed to your stove. 8" scraps of 2x are going to burn quick no matter how full you stuff the stove.

 

[windthrown]

Greenhouse boiler feeding...

It is a cozyburn 250.
I am trying right now at 3 am to keep the water temp up.
I am loading in 8 inch pieces of scrap 2x4 and other pallet pieces along with used cooking oil and a stihl leaf blower .
my greenhouse is full of plants tottaling just over 6 grand so if they get cold they die.
winter hit hard again with alot of snow and wind.
but when my wife is selling plants and has a smile it is all worth it.
total crap for me so i will be buying a better unit.
.

shayne

Sounds like you have a reasonable 250k BTU wood boiler (as opposed to that guy that posted about his Ebay special OWB that filed to ever work, or the other owner with the Royall pain in the arse that blew up). In that case I would up my estimate and I think you need more like a 400k-500k BTU burner. Peak demands can really suck up firewod here when it is cold (cold here is 15 degrees). If you have access to a lot of pallets there are pallet burners out there that are rated at 500k BTU. I know Central Boiler sells them. Dual fuel boilers allow you to burn high BTU fuel in really cold spells. You can get them with dual fuel and burn one of NG, oil, or LP gas in them along with wood. Coal may be better and easier at that price though.

You might also consider that your boiler is just undersized. Maybe leave it hooked up to your house and garage, and get a 250k BTU wood/coal burner for the greenhouse? I am thinking of adding a greenhouse here near the house. We have gobs of space, and the boiler has plumbing for a second PEX line and room for another Taco pump on that loop. My orchids are down in California being babysitted for me in Carmel. They would freeze to death here in one night in the teens.

 

[bassman]

right now i have the house shut off and i am only heating the greenhouse .
I simply need a bigger output and i want to get it without burning just wood.
I like the boiler and it works well when it is not trying to do too much and i am not here to bash them as they have there place .
I also think coal is way hotter than wood but again I dont know and i dont want to have to spend 5 grand to find out.
I have a big post coming later .

gotta go

shayne