Used wood boiler?

[Komrade]

Brief history/background:
I have a log home. It's heated with a Fujitsu Mini-Split
After I built an addition, the mini-split was not enough.. I started supplementing with wood burning (internal wood stove).
The house (ground floor) is prepped for warm water (insulation under, many loops of pex piping)
At some point I considered heating that water with a SanDen unit.. The unit is great, about 6x more efficient than a typical electric heater, but not nearly as efficient as mini-split which have a SEER rating of 20-35 (20-30x more efficient). Plus it's meant for hot water, not heating and limited in capacity even if I abused it (15K BTU)
Since I live in the boonies (and neighbors have been w/o power for a week), I would prefer to have the peace of mind of being somewhat energy self-sufficient (I also have about 15K Solar array, battery and generator backup) I am back to looking at wood boilers as supplemental heating system (I am still not sure I'll love splitting so much firewood and feeding it twice a day.. In the past I have looked at Wood Gun (recommended by my builder, and about an hour+ drive from me). I ruled it out due to cost, although the SanDen unit would be fairly equal (but likely undersized from BTU perspective)..
I am fairly confident I need to stay on the smaller side of available boiler. (Footage of the house, including unfinished space is around 2500 ,BTU needs are not finalized as insulation can still be added)

I am reconsidering a wood boiler that I would put outside in a shed, and pair with storage and water solar panels that I have lying around.

There are currently 2 relatively close on CL

1) Wood Gun E100 that is estimated to be 15 years old
2) Econoburn EBW-100, age not listed

I understand the Wood Gun as I researched it plenty.. I understand it's a quality unit, however, what Q's would you ask if buying a used unit and what maintenance should I expect to do sooner rather than later on an older unit?

Thanks,

 

[Seasoned Oak]

I think your off on the SEER rating efficiencies. Your minisplit may be 2 or 3 times more energy efficient ,not 20 to 30.

 

[Komrade]

Um.. thank you. I guess I haven't looked at that in a while and had 1BTU=1Watt in my head, which is incorrect
1Watt = 3.41 BTU.. so 1000W electric heater is 3400 BTU/hr.
36000BTU 16SEER Fujitsu is 2250W/hr or 16000 BTU/1000W, so about 5x more efficient..
I feel like my math is still off somewhere, but seems like any SEER rating can be divided by 3.41 to compare to "direct electric heat"
Forum induced (re) discovery may change my planning..
Thanks again for pointing this out

 

[salecker]

I have an Econoburn.This will be the 11 or 12 th year.
I would not hesitate to buy an Enconburn again.Even used units would be worth a look.Other than soot on the outside of mine there is nothing to show its as old as it is.

 

[maple1]

A bit uncertain - you have considered a SanDen, or you actually have one in operation?

I had no idea what that was, had to Google it. IMO that looks very interesting for a thing like this, and I would be considering it - a boiler & storage setup is a very big step to take, money & logistics. How long have they been sold? How much do they cost? Looks kinda like what Highbeam has been searching for all these years - hope he sees this.

 

[peakbagger]

Air to Water Units are the current product that the heating gurus are pushing. John Segenthaller is a hydronics guru who writes for PME magazine and is really pushing them and has written several articles about using them recently. If you search around for PME magazine you can find his articles in the back issues The problem is not a lot of mainstream companies are selling them yet in the US. They only work well when paired with radiant heating devices designed for low supply water temperatures (120 F mx). That low temp means higher over all system efficiency with some major side benefits including far more effective use of storage if paired with wood boiler or other high temp source and the ability to tie in solar hot water. My suspicion is like mini splits, there just isn't a lot of heat in the air at temps under 0 F. Thus in cold climates their CIOP drops quickly when most homeowners need more heat.

Anytime you talk wood boiler you need to talk about storage. You really shouldn't have the boiler without the storage. So plan on adding a few hundred gallon thermal a storage tank to the mix.

 

[Komrade]

I do not have one, but been looking at it since last year.
for pricing
(broken link removed to https://foursevenfive.com/sanden-sanco2/)


my plans as they unfolded when I was looking at it:

Sanden EcoCute + Instant Heater as backup radiant design

This project started out as a solar heating project, and you can read about it here

forum.heatinghelp.com

I'll check out PME magazine and articles.. I think I may have stumbled on name/magazine before... ah yes, the gentlemen has written some books that I may want to consider reading.

Sanden works down to fairly low temperatures with 100% capacity (i think about 5F). It's been on sale in US for a few years, and there are a lot of research articles.

 

[Highbeam]

A bit uncertain - you have considered a SanDen, or you actually have one in operation?

I had no idea what that was, had to Google it. IMO that looks very interesting for a thing like this, and I would be considering it - a boiler & storage setup is a very big step to take, money & logistics. How long have they been sold? How much do they cost? Looks kinda like what Highbeam has been searching for all these years - hope he sees this.

I found reference to the Sanden units in a green building article and searched the product. Ruled them out because they cost about 5000$ and only make 15000 btu max. Plus some oddball manufacturer I had never heard of so no real reputation. It did put out high temperature water, like 150.

 

[Komrade]

The heat pump w/o stainless steel storage is $2200.

World Class Supply - High Performance Building Supply & Design > Sanco Water Heater > The SANCO2™ Heat Pump Water Heater

Sanco Heat Pump Water Heater is a two-part system consisting of a tank and a heat pump unit. The heat pump works like a reverse air-conditioner, drawing heat energy from the atmosphere and applying it to water in the tank

worldclasssupply.com

I think the manufacturer and technology are well known and proven in APAC.
However, as I said above, it's ready meant mostly for hot water, not for heating.

 

[maple1]

I found reference to the Sanden units in a green building article and searched the product. Ruled them out because they cost about 5000$ and only make 15000 btu max. Plus some oddball manufacturer I had never heard of so no real reputation. It did put out high temperature water, like 150.

Kind of thinking that your shop wouldn't have a huge heat load? Just to keep the chill off? Not really sure though. Ever run any numbers? Once you get the slab heated, it would likely steadily coast along great without a whole lot of BTUs.

Over time, I have figured our house averages 35,000 btu/hr over the whole winter. At $2200 mentioned above, for one unit., I could theoretically get 3 for $6600 and cover all our heat load with a little to spare. That's a pretty attractive price for a hands-off heat generation source that could do all our heating.

Hopefully a sign of more widespread same tech to come, over more common & 'brand name' manufacturers.

 

[Highbeam]

Kind of thinking that your shop wouldn't have a huge heat load? Just to keep the chill off? Not really sure though. Ever run any numbers? Once you get the slab heated, it would likely steadily coast along great without a whole lot of BTUs.

Over time, I have figured our house averages 35,000 btu/hr over the whole winter. At $2200 mentioned above, for one unit., I could theoretically get 3 for $6600 and cover all our heat load with a little to spare. That's a pretty attractive price for a hands-off heat generation source that could do all our heating.

Hopefully a sign of more widespread same tech to come, over more common & 'brand name' manufacturers.

I actually found one for sale and it was just under 5000$ plus our 10% sales tax. Not 2200 and not a well known brand. Even at 2200 it still is just 15000 btu. When I did the heat loss calc0s on the shop I needed almost 30k btu on my design day. So two of these Sandens for 10,000$

A regular electrical resistance boiler of 10,000 watts will make that much heat for under 1000$ with no moving parts.

I'm going to either use an electric boiler or wait for a name brand heat pump water heater that can make 30,000 btu for water heating. Surely the markets are close to doing it with items like this Sanden.