Need wood boiler and water storage advice

[jim_n_nh]

Hello everyone,

I live just outside of Manchester NH in a very energy efficient Structual Insulated Panel home that is partially earth bermed. House is basically a ranch (1 story with basement). On the north and west side the first 4 feet of the house is below grade. The south side and East side are walk out. House is 38' by 46' and the long side faces true south and gets substantial solar gain. The house calls for 24,000 btu to heat. While I have radiant floor heat with a 40 gallon propane hot water tank to heat it we use a Woodstock soapstone wood stove in the basement to heat it. The Tarm system is nice but simply to expensive. I would like to have enough storage so I have to fire up only every 2 to 3 days. Please help.

I forgot to mention that I only go through 2 to 2 1/2 cords of wood a year and no propane.


Jim

 

[Eric Johnson]

Welcome to the Boiler Room, Jim. If you can get away with not having a gasifier, you can pick up a conventional wood-fired boiler for around $4,000, and maybe less. There are also many used ones for sale for less than $1,000. To fire every two or three days, however, you're going to need some hot water storage. If you're a DIY type, I'd suggest doing some research and building your own.

If you want a gasification-type boiler, you might want to check with Windy Ridge Corp. in Tamworth. They have a nice looking Finnish import that's not very expensive, as I recall. Or, click on the Cozy Heat banner at the top of this page. They have pricing for the EKO line, which is a bit less expensive than Tarm, last time I checked.

 

[sparke]

Yes Windy Ridge has a Boiler/storage tank combo. The Boiler is around $2700 and the tank is around $3500 if I remember correctly. (I priced them at one time so this is from memory). FYI-their boiler is a downdraft so it requires a strong draft... Also, their boiler needs short wood if that is important to you...

 

[steam man]

You may want to think about some active solar collectors. For the price of a wood boiler system installed and the amount of wood you use I am not sure its worth the hassle to deal with the wood. Leaving what you have in place for the peak heating needs would seem to be prudent. For what your trying to achieve (the luxury of just burning every two or three days) doesn't seem to warrant the expense or hassle considering your still going to burn wood. I hope I don't get kicked off this forum for sounding anti-wood burning. Everyone should just think of it as leaving more wood for the rest of us. LOL.

Mike

 

[jim_n_nh]

Thank you all,

Solar is one angle I am currently looking into but when I talk to sales people I get "I think it will work" vs "it will work". My house is made to be offgrid but my first step is heating. I have looked some at (broken link removed to http://www.nationalstoveworks.com/Basic%20Info.htm) model 400 but I have not heard of anyone using them. I need water storage and judging from the threads here in hearth.com that seems to be a common area of concern. How big of storage would I need.


Please keep the comments/suggestions coming I want to learn and hear from people that have done it.

Thanks again,

Jim

 

[ericjeeper]

My view on radiant slab, I am assuming he is referring to in slab heat. Ok a slab sucks the life out of storage.It is not like an air to water hx.Figure it is coming in at 120-160. Then it runs through the tubing in the floor.The floor brings the temps down hard and for long periods of time.
For instance when my garage calls for heat there is almost 1,000 feet of pex at a temp of 65 degrees By the time the hot water goes through it. It leaves at 80-95 all depending on the temps coming in and how many other zones in the house are open at the current time. I have a 600 gallon tank and when the garage and living room both come on at the same time the temps fall pretty quick. My forced draft blower comes on when the tank drops to 145, I have had days after a warm spell when the temps dropped that the blower would run for 5 hours straight trying to get the tank temps back up.But as long as the slab is calling for heat it pretty much just keeps even.
My heat loss is 26 k. It does not take a lot of heat to heat my house on average. But you have to think differently when it is banking the slab up. as opposed to just blowing warm air into the room.

 

[Nofossil]

Hello everyone,

I live just outside of Manchester NH in a very energy efficient Structual Insulated Panel home that is partially earth bermed. House is basically a ranch (1 story with basement). On the north and west side the first 4 feet of the house is below grade. The south side and East side are walk out. House is 38' by 46' and the long side faces true south and gets substantial solar gain. The house calls for 24,000 btu to heat. While I have radiant floor heat with a 40 gallon propane hot water tank to heat it we use a Woodstock soapstone wood stove in the basement to heat it. The Tarm system is nice but simply to expensive. I would like to have enough storage so I have to fire up only every 2 to 3 days. Please help.

I forgot to mention that I only go through 2 to 2 1/2 cords of wood a year and no propane.


Jim

At 2 1/2 cords per year, that 24,000 figure must be per day, not per hour!

I assume that it's actually a peak of 24,000 per hour on your coldest and windiest day. 2 1/2 cords at a generous 50% delivered efficiency would give you something like 30 million BTUs. Over a 120 day heating season, that works out to an average of 250,000 BTU per day. With radiant, you can use water down to about 90 degrees, especially in your situation. The highest storage tank temperature that I'd plan on would be 170 degrees, giving you an 80 degree working range. That works out to 664 usable BTU per gallon of storage. Two average days would be 500,000 BTU, which would require about 750 gallons.

A note on assumptions: I'm basing this on wood consupmtion and an estimate that you're getting half the theoretical energy out of the wood that you're burning. That may be optimistic, in which case you could get by with a smaller tank. If you have a better estimate of average heat load, you can crank the numbers yourself.

In your situation, I'd do what I did here and make provisions to heat the storage with solar, using wood as a backup and fossil (oil in my case) as a last resort. I'd also plan on getting domestic hot water out of it as well. You can check out my setup - link is in my signature below.

 

[tuolumne]

A wood stove will never be as hungry as a wood boiler, but never provide the comfort either. We heated our last house with 2-1/2 cords of hardword per year in a Hearthstone Mansfield. Those soapstone stoves (plus an interior masonry chimney) can be very efficient. The house was 2400 square feet with a peak demand of 80,000 btus/hr. This year in VT we've already used over 2 cords using a cast iron stove in an old house. I've seen an 18kW Eko in the brochures. I don't know if anyone actually sells those in the U.S., but perhaps New Horizon could get one over here with a little time. I would think that small boiler and a 500 gallon propane tank would be a good combination for your small demand.

Thanks for a quick demonstration with the numbers nofossil. You make me optimistic that 1000 gallons will take care of our new home fairly well. The peak demand is 65,000 btus/hr at -20 degrees, but that was accounting only for R-value. We're using 2lb foam, and the limited infiltration probably means our needs are actually lower.

 

[jim_n_nh]

Thank you everyone,

It is reassuring that my uneducated guessimates are close to what is being expressed in the replies. My initial thught was to have solar hot water heaters dumping into a storage tank. The storage tank would preheat/heat the DHW and/or radiant floor heat. Down stream of the storage tank I would have on demand hot water heaters that could handle the input being preheated.

I was hoping to have the storage so I wouldn't have to feed a stove all the time because my wife and I can be away for 14-16 hours at a time, several days in a row.

The radiant heat is underneath my hardwood floors and not in the basement slab..

Thanks again for the suggestions.

 

[SteveJ]

Something you might consider is to have two storage tanks instead of one large.

Have one tank large for radiant and one smaller tank for DHW.

As nofossil points out, the radiant tank can be drawn down to 90F; whereas DHW requires tank temps of 120F or higher.

Issues would be maintaining stratification in both tanks and the increased cost of HX for both tanks.

Hopefully, someone else can elaborate on the benefits of two tanks versus one.

If you could stack the smaller tank on top of the larger, then you could also take advantage of thermosiphoning.

nofossil has a comment on two storage tanks in this thread https://www.hearth.com/talk/threads/13512/

 

[ISeeDeadBTUs]

Um . . .yes, concrete suck the life out of your boiler when trying to heat up, but

the temps going in are way lower than 140 deg :gulp: and
the mass of the concrete will help heat the house for longer periods after the 'heat goes off'

 

[ericjeeper]

Um . . .yes, concrete suck the life out of your boiler when trying to heat up, but

the temps going in are way lower than 140 deg :gulp: and
the mass of the concrete will help heat the house for longer periods after the 'heat goes off'

Yes The floor will hold heat for long periods of time.. Especially when company comes for the holidays. Nothing like Christmas with the windows open. we can have 20 people in our great room starting out at 72 degrees within an hour or there abouts it is well over 80..No one wears a sweater to my house. LOL

 

[ISeeDeadBTUs]

But does your SIL look good in a T-shirt when it gets drafty??

 

[jebatty]

But does your SIL look good in a T-shirt when it gets drafty??

Huh? SIL, Squamous Intraepithelial Lesion, intraepithelial neoplasia of sqhamous epithelium or inflammatory lesion which mimics intraepithelial neoplasia in gynecological area (especially in cytology based on Bethesda system).

 

[ISeeDeadBTUs]

Sounds like you've met my SIL :roll:

 

[Tony H]

My moms house has a gas boiler with a slab and radiant heat and while it will run for a bit on a cold sunless morning the advantage is with a good southern exposure it will go for several hours in the afternoon / early evening with out running much at all as the concrete absorbs and gives up its heat back to the house.
She also has a gas forced air furnace for the air conditioning and backup and when my Dad ran and compared them the boiler (20 years old) was more economical to run than the 90% forced air furnace.