wood/oil combination boiler

[hemlock]

Hello,
New here. I'm considering installing a wood/oil combination unit in my home. Currently, I heat with wood, but unfortunatley, my DHW is oil fired. If I were to install a wood/oil unit, would there be an excessive amount of re-plumbing to do, as well as thermostats and controls to add in? As well, the chimmney would have to be replaced I assume (5" flue now). Does anyone have any advice or expereince with this? Thanks.

Husky 137
Husky 50
Husky 262xp
John Deere Loader

 

[hemlock]

Sorry,
Wood stove, oil burner for DHW and radiant heat. (Don't use radiant heat)

 

[Vtgent49]

If you already have a decently designed radiant heat system (unused) and an indirect DHW system, then you are already 90% of the way there. Switching your present oil only to wood/oil or even to a wood boiler combined with your oil boiler seems like a "relatively" easy move. You should consult a local expert installer for quotes, as what is often discussed on here is do-it-yourselfer stuff, that admittedly may seem quite overwhelming.

But frankly, if your oil boiler is hot for 12 mos. of the year, just to heat DHW, PLEASE seriously consider a newly designed system (for the Earths sake). Or even a used Tarm wood/oil system from the 80's, which could slip SO Easily into the place of that oil burner. I have a simplex brand wood/oil, and solar panels for Summer DHW. It's not very exotic, but has 90% of the benefits of these state of the art systems often discussed here.

5" is small, but is that from the boiler to a masonry chimney? If so, a 6" is easily installed. The masonry chimney may be 6x6, or 6x8 or bigger?

 

[hemlock]

My oil boiler is running all year just to heat water. I would like the option to use wood, as we heat about 6 to 7 months of the year. Using a wood boiler would save a tremendous amount of oil. I am unsure of how they work, however. When the water reaches temperature, how does a wood boiler slow or stop combustion? An oil boiler simply shuts off, but wood must continue to burn, so where does the excess heat go? My flue is 5" all the way up. It is a selkirk. It would have to be replaced, i'm sure. Thanks for your help.

 

[Gooserider]

Welcome to the boards Catfish, hope we can help you out... You will get a lot of benefit from reading as much of the past threads that look interesting as you can stand :lol: then we can help fill in the parts you still have questions on...

As a very basic minimum...

There are two basic approaches with a gasification wood boiler, one more expensive and complex initially, but FAR more efficient, especially in the non-heating season, the other easier, but less efficient.

The easy way is to just slap a wood or wood / oil burner in place of the oil burner - as you said, sounds like you might need a new chimney, otherwise nothing to terrible in the way of added plumbing. The way it will work, is that you build a fire, and the house demand draws heat until it's satisfied, at which point the boiler will go into "idle" mode, where the air is shut off almost totally, keeping just enough to (hopefully) keep the fire burning. When the demand returns, the air turns back on, the fire heats back up, and the cycle repeats. While this works, it is very inefficient, can make for lots of smoke when the boiler comes off idle, and is not a real optimal approach.

The preferred method is to use thermal storage - usually a large tank of water (500 or more gallons) plumbed alongside the wood boiler. With storage, the boiler is run flat out, at it's maximum burn rate until the fire is done - any heat that isn't used to heat the demand is used to heat the storage tank. After the fire goes out, the demand draws from the heat stored in the tank until the tank temperature drops down, at which point you build another fire in the boiler. There are a lot of aspects to sizing the storage tank and boiler, but when properly done, most people will find they only need to fire up the boiler about once a week in the summer if all they are making is DHW. As the weather gets colder, you will need to fire more often, until you reach the point during the coldest temperatures where you will need to fire just about as often with storage as you would have without it. The other big advantage of storage is that it makes it very easy to tie in additional heat sources like solar, which can totally eliminate your need to run the boiler in the summer.

Hope this helps.

Gooserider