How Much/What Kind of Storage For a 25KW Wood Boiler?

[velvetfoot]

Hi. This is all roughly speaking. I have a 10 year old, 2000 ft2 colonial, in upstate NY, with a Burnham oil boiler set up for 79,000 BTU (net). I figure a 25kW (85,000 BTU) output boiler, like the Vigas, would be a good match. Would 500 gal storage be appropriate? I have a 36" door to work with. There are the fancy factory storage tanks that are, like, 200 gallons each. Maybe a 500 gallon propane tank would fit, but then require welding fittings, cleaning inside and out, painting and insulation. Or, an unpressurized solution like a Heat Bank would have no problem getting through the door.

Any opinions? Thanks.

 

[flyingcow]

Whats your avg oil use per yr?
Have you ever done a load calc?

FYI- I have a 1800 sq/ft 2 story house in northern maine. Avg insul. Was using about 1000 gals of oil yr round. My oil burner is a 85,000 btu. Kept up, just barely in the -30 to -40 outside temp times. Would maintain the house at 68/70 but it seemed to be running the majority of the time.
I put in a 102,000 btu gasser with 820 gal unpressurized storage. I figured the rated output of the gasser should be 15/20% more than the oil burner. Everything works well. If I was to do over again, might have put in 1000gals of storage. But I had limited basement access and the tank i bought was one i assembled in my basement. The company now offers a 1100gal tank, didn't back in '07.

The house is 18 yrs old. As time goes on I am finding air infiltration and trying to seal them up as I find them. Looking back, I wish i would have stepped up the r-value when it was being built and paid closer attention to the little stuff. All I have is r-19 in the walls and maybe r-35/40 in the ceiling.

A heat load calc would help you size everything. Your delivery system? Baseboard? Radiant? Hot air? The delivery system is important info.

 

[velvetfoot]

Yeah, I hear you about delivery. Alas, it is tube/fin baseboard.
The house is pretty tight. I have ideas about heating/semi-finishing the basement, but all the additional boiler stuff won't help with that, but if it does fly, would add some more heat load. The basement walls are insulated.

You have no problems charging the 820 gallons?

I'm trying to figure out the best combo of boiler and storage. It goes against my grain to buy an oversized boiler, since it is sized for a design day, just to charge up a large storage. Would ideal be that it would be large enough to absorb a complete burn to ash?

Those heat banks tend to be square, right?, which eats up maybe more room. Along with the boiler and some wood storage.

We don't see -30, knock on wood: got down to -11 the other week. We have an insert that does a pretty good job now, but the upstairs are usually 60 ish, depending on how cold it is outside. Would be atmosphere if boiler is in future, but could also boost heat on really really cold days.

The walls are 6" fiberglass, and I had a bunch of fiberglass blown in the attic and put foam on the rim joist while I did the basement walls. As I said the house is 10 years old and was built to code.

 

[flyingcow]

I have BB too. The more I learn here, I'm figuring out my installer just threw baseboard here and there according to his experience. He was a good old heating guy, but I should have done a lot more research in heating and design. Overall, the house is balanced pretty decent for a 2 zone house. So he did good. I've had the great idea of putting in more staple up and low temp emitters. Still dreaming.

Later on I did put staple up underneath my kitchen floor to keep the feet warm. Thats only about 25% of my first floor space.

I have no problem charging storage. The HX's that came with the tank do a really good job. In the summer I can bring the tank from 115/120 to 165+ on one load. Thats as far as i go in the summer for DHW. I bring the tank up to 180 with the weather we've had the last 6 or 8 weeks. Even had to do a second fire in 24 hours a few times. I think the firebox is 4.5 cu/ft. Thats with good dry wood and clean tubes.

When I was looking to buy a boiler, I got some info(can't remember where) about a wood boiler should be a little bigger than an oil boiler. Or any boiler for that matter. Thats why i went with a 30k unit. Also, it was the smallest unit in the product line I wanted.

I met Mark at AHONA a couple of yrs ago, at a trade show in Maine. I assume thats who your dealing with. Seemed very knowledgeable. Good to talk to. I also got to look at the Vigas up close. I liked it. He had his demo trailer with one running plus had one on display. If he says what size will work best for you, thats what i would go with.

Important info--I am not a heating pro, truck driver by trade.. Just can't sleep and this site is a good bunch of people.

 

[flyingcow]

Also, I agree in not over sizing. Which I was happy with the sizing of my weil-mclain oil boiler. I had no problem of the oil boiler running flat our for that week or to of serious january weather. Haven't really had -40 for a long time. But these last few weeks have been pretty brutal. But with storage, it will give a little flexibility in sizing of boiler. Once others wake up, they will chime in and give you better info than me.

 

[maple1]

330 gallon LP tanks are 30" x 9'. I've got two of those stacked, and they don't take up a ton of room. But I stacked mine outside, then rolled them in. Stacking them in the basement would be kind of tricky, methinks. You could also arrange several 110 gallon tanks to fit your space. They're 30" x 4', +/-. Would require more plumbing to get them all hooked up, but would be way easier to handle in a more restricted space. They are still kinda heavy though.

By the sounds of it, I would think a 25kw boiler would meet your needs - I would try to max my storage though. I would like to have 1000, but the 660 is doing me good.

 

[Clarkbug]

Hi. This is all roughly speaking. I have a 10 year old, 2000 ft2 colonial, in upstate NY, with a Burnham oil boiler set up for 79,000 BTU (net). I figure a 25kW (85,000 BTU) output boiler, like the Vigas, would be a good match. Would 500 gal storage be appropriate? I have a 36" door to work with. There are the fancy factory storage tanks that are, like, 200 gallons each. Maybe a 500 gallon propane tank would fit, but then require welding fittings, cleaning inside and out, painting and insulation. Or, an unpressurized solution like a Heat Bank would have no problem getting through the door.

Any opinions? Thanks.

I dont think Im too far from you actually velvetfoot....

I have a boiler rated at 37kw and I have 660 gallons of storage. I live in a drafty old farmhouse that is getting better as I work on it, but its enough storage that I can fire twice a day and usually keep the house at 68. With the wind and bitter cold it drops a few degrees.

I salvaged 3 220 expansion tanks from an old school that was getting its boilers replaced, and they work well so far. Had all the right tappings on them, and fit into my basement. Plus the price was right!

Tom in maine sells the unpressurized tank that you can build on your own, or you can talk to Smokeless Heat, as Varmebaronen sells square tanks that fit through a doorway. Cheapest way is definitely to find a scrap propane tank, but your time is worth something too.

 

[Chris Hoskin]

we use a general rule of thumb where we recommend a minimum of 40 gallons of thermal storage per 10,000 btu of boiler output and an ideal of 70 gallons per 10,000 btu, so a 500 gallon LP tank or Tom's 550 unpressurized would be right in there as would two 220 tanks if you are buying pressurized off the shelf. What you end up with will also be strongly influenced by budget and what you can get into the room, of course.

 

[velvetfoot]

Thanks. I drove over to AHONA today and had an great, informative time. Of course, I have more questions now.

Like, maybe 25 kW isn't right for me since I have so much 16" wood and that is what the insert uses. It could in fact, be derating it since the boiler is rated for the capacity which is like 22". The 40 kW isn't that much more expensive. Apparently the 500 gallon propane tank is 37" in diameter, which could fit through the door if the frame was removed. I guess it might be possible to stack two 500's.

Assuming I go with Mark, there's the question of Vigas, (lambda, steel), with Viadrus Hefaistos, (cast iron, no lambda). In the hefaistos, 25kw is not possible because it requires, like, 13" wood. The Viadrus looks very impressive and tank-like.

It was nice to see the Vigas go through its paces.

 

[flyingcow]

How long is the firebox on the 40?

 

[velvetfoot]

On the Viadrus Hefaistos 4 section, 136,480 BTU/hr max, 19.49".

 

[velvetfoot]

I found a YouTube video on a larger Hefaistos, and replacement of nozzle seems like a complex operation. Maybe even very complex, compared to others where you can take the old one out and pop a new one in. I'm not sure I'm necessarily a devotee of cast iron as well.