Add-on Wood Boiler

[Marshy]

Hi guys, I'm tired of trying to heat my house with a free standing stove and I've decided its time to add a wood boiler to my existing hydronic system. I'm starting this thread because there seems to be a lot of options and so much information available its a little overwhelming. I'll have questions along the way and would appreciated your feedback/knowledge/direction to resources as I try to put together a system and balance cost with reliability.

The installed hydronic system has a Utica Boiler, 4 heating zones with finned baseboard heaters and 1 zone for an indirect hot water heater. I will get the rating for the boiler later but suffice to say its either 95K or 105K BTU size. The system is closed and operates at 10psi.

I would like to incorporate thermal storage in the system. I found a forum member nearby me selling a 820 gal unpressurized thermal storage tank with a 100K BTU heat exchanger. My goal is to purchase the tank and install it in my basement. I would use the 100K HTX to provide heat to the house loop. I would like to keep the boiler a closed looped and use antifreeze so I will likely get a HTX for that side of the loop (probably 150K BTU HTX).

Questions I have right now are, what size boiler should I be considering, is 150K BTU large enough?
There is a used (indoor) ECOBURN 300K BTU boiler for sale nearby for $4500 that was manufactured in 2013, thoughts?

Thanks in advance.

 

[NateB]

That heat exchanger should be use to provide heat to the floors and put heat into the tank from the wood boiler.

The 300k boiler will be too big for that tank heat exchanger combination.

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[Marshy]

Thanks for the input. I just spoke with a rep at ECOBURN and he suggested that I put two 150K HTXs in parallel on the boiler loop to heat that tank. He said the 100K HTX might be fine for the house side of the loop but mentioned the boiler will easily go into idle mode if it cannot get the heat into the tank making the boiler very inefficient.

I also talked with the manufacturer of the tank and he said that 820 gal is actually on the smaller side that they would recommend for my area of NY.

Regardless, it sounds like having enough heat transfer is going to be key.

 

[NateB]

I bought my tank and HX from Tom. He was a big help for me in getting my system setup. I used primary secondary plumbing on my system, and I used supply house.Com for all my fittings. Webstone Purge tees helped in simplifying the install.

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[Highbeam]

Good thread, I'm following. I can't imagine a 300k btu boiler being anywhere near the right size for what you're doing. Way too big even though I realize that the rate of output just means it will take less time to charge the tank.

 

[NateB]

If the HX can out put the BTUs in to the tank fast enough. I think what would happen even with small loads of wood is that the boiler would have a tendency to over heat, because it will put out BTUs faster than the HX can use them.

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[Marshy]

If the HX can out put the BTUs in to the tank fast enough. I think what would happen even with small loads of wood is that the boiler would have a tendency to over heat, because it will put out BTUs faster than the HX can use them.

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Yes, there is benefits and draw backs if I oversizing the boiler. The benefit is can heat my storage rather quickly. The down side is I have to spend more in sizing the proper heat exchanger to keep the boiler from entering idle mode and wasting efficiency and fuel.

The Ecoburn 300 I was looking at a 300K BTU output but is priced very reasonably at $4500 and It's a 2013 model. Ecoburn said if I give them some info on the manufacturing plate they can tell me if it's ever been warrantied and how it was installed originally (commercial or residential).

 

[Highbeam]

So you want to burn the whole firebox load at high output to charge your tank and then use the tank's heat over the next day. You know that the output at full burn is 300k. So do you just vary the amount you fill the firebox based on temperature of the tank so as not to overshoot the desired tank temp and cause the boiler to idle?

 

[maple1]

Was that Econoburn used with storage? Do you know what it was heating?

As already mentioned, a boiler that big would have lots of potential for idling if it wasn't sized right for the application it was in, especially if it wasn't tied to storage from day 1. So if it wasn't (improper procedures could do it too), I would be leery of its condition even if it is a 2013 - there could have been corrosion going on in its firebox for the time it's been in service that might not be evident. You could likely get a more properly sized boiler, new, for maybe 50% more money?

Just a thought. Otherwise, adding an extra HX might be a small price to pay to get what you have lined up, working properly together. If you go that route I would go to Tom for one, and bend his ear while there for suggestions. He knows stuff.

 

[maple1]

So you want to burn the whole firebox load at high output to charge your tank and then use the tank's heat over the next day. You know that the output at full burn is 300k. So do you just vary the amount you fill the firebox based on temperature of the tank so as not to overshoot the desired tank temp and cause the boiler to idle?

Sounds right.

 

[Marshy]

So you want to burn the whole firebox load at high output to charge your tank and then use the tank's heat over the next day. You know that the output at full burn is 300k. So do you just vary the amount you fill the firebox based on temperature of the tank so as not to overshoot the desired tank temp and cause the boiler to idle?

Yes, that's exactly the purpose and how it would work, ideally.

With the back of the napkin calculation I could see how many BTU's it would take to heat my storage tank across an assumed temperature band. The larger the difference in temperature of the storage tank the more BTUs required and the better I can utilize the capacity of the larger boiler. It may be unpractical to get that 300k boiler even if I do partial fuel loads. I have to believe there is some sort of penality to the boilers efficiency when loading half a load vs full.

That asside, the potential draw back of my currently installed hydronic system (base board) is they are relatively inefficient at lower water temperatures. That may require me to control the storage tank temp between 160-190 vs 130 or 140-190. Having a larger delta T in storage is a blessing and something like in floor heating is very forgiving at lower water temps compared to baseboard. Controlling a narrow temp band in the tank is counterproductive in many cases because it increases the firing cycles of the boiler rather than letting it run full speed for the duration of the fuel load. It's a balance that needs considering.

Was that Econoburn used with storage? Do you know what is was heating?

As already mentioned, a boiler that big would have lots of potential for idling if it wasn't sized right for the application it was in, especially if it wasn't tied to storage from day 1. So if it wasn't (improper procedures could do it too), I would be leery of its condition even if it is a 2013 - there could have been corrosion going on in its firebox for the time it's been in service that might not be evident. You could likely get a more properly sized boiler, new, for maybe 50% more money?

Just a thought. Otherwise, adding an extra HX might be a small price to pay to get what you have lined up, working properly together. If you go that route I would go to Tom for one, and bend his ear while there for suggestions. He knows stuff.

I called Econoburn and asked them if they could share any info on the boiler, like if they did any warranty or repairs based on it's serial number. He said he would be happy to provide me what he has. I gave him the serial number but he needs the safety certificate # to verify the info. He said if it's the one he believes (based on the serial # alone) he believes it could have been installed originally at a state college in the forestry maintenance building. The seller bought it and was going to install it on another property he owns but decided not to. I've asked him for the safety certificate # so I can follow up with Econoburn. He said if that is the one, he has plenty of history to share, and I tend to believe the installation would be top notch at a facility like a state college. BTW, that boiler is $10,500 new before NY tax, and I asked what a refurb of the entire boiler would cost, he said they just refurbed one in bad shape for $3-3500 and he basically left with a new boiler.

 

[Marshy]

Here's a good reference for calculations. Theses will come in handy later.

http://www.plumbingperspective.com/key-water-heating-charts/

BTU= (#gal x 8.3 x (delta T))

BTU= (820 x 8.3 x (190-160))
BTU= 204,180

BTU= (820 x 8.3 x (190-150))
BTU= 272,240

More to follow.

 

[Chris Hoskin]

Here's a good reference for calculations. Theses will come in handy later.

http://www.plumbingperspective.com/key-water-heating-charts/

BTU= (#gal x 8.3 x (delta T))

BTU= (820 x 8.3 x (190-160))
BTU= 204,180

BTU= (820 x 8.3 x (190-150))
BTU= 272,240

More to follow.

Marshy, that would suggest that the 820 tank could store about one hour's output from the big Econoburn. I recommend you either look for much larger thermal storage or (better) a smaller boiler.

Also, no need to have separate input and output coils in the tank, one coil can do both. PM me or email me at [email protected] if you'd like me to send a schematic.

 

[Highbeam]

Here's a good reference for calculations. Theses will come in handy later.

http://www.plumbingperspective.com/key-water-heating-charts/

BTU= (#gal x 8.3 x (delta T))

BTU= (820 x 8.3 x (190-160))
BTU= 204,180

BTU= (820 x 8.3 x (190-150))
BTU= 272,240

More to follow.

That tells the story. A 300,000 btu boiler could only make heat full output for an hour before dropping to idle. If you consider warm up and cool down output it will probably never even be able to get fully warmed up. Looking at the popular tarm options, their output is way lower. The 166k btu output model has a 7CF ft firebox. It doesn't take many #s of wood to get 280,000 btu. 8600 btu per # means only 33# of wood which is only a half load in my little woodstove.

I read here that most folks with these wood boilers shoot for a three hour burn so a sub 100k btu boiler would be more appropriate if your "charge" is near 300kbtu.

The tank can release 280k btu before getting too cold. Is that enough over 24 hours to keep your house warm? 12000 btu per hour is like a 3500 watt electric heater.

It looks like you have too much boiler and not enough storage for your emitters. If you could take advantage of lower water temperatures then the 820 gallons of storage will go a lot farther.

 

[maple1]

A couple of other things to consider.

Your baseboard might do better than you think at lower temps. Mine did. It seems to have been over engineered a bit when done 20 odd years ago, but I didn't discover that until I started heating from storage for a while. Which I am now very thankful for. I don't really feel a need for more heat or feel that the house is losing heat until my storage temps get down & below the 140 range. But you likely won't really know for sure until you actually do it, no matter how many heat loss numbers you run.

You could also add more emitters - hopefully? Either more baseboard, or maybe a cast iron rad in select spots? Mine (Slant Fin) was installed with the enclosures going the full wall length in most rooms, so I still have lots of places where I could add more by just cutting in fin sections under the existing enclosures. And cast iron rads are usually pretty easy to find used.

I also stretch my storage most of the time, by doing small setbacks during the day, then I burn in the evening when the house needs the heat, at the same time as the storage is depleted. And I run the stats (programmable) up a degree or two past what I might otherwise maintain in the evenings. So maybe half the boiler output, for maybe half the burn, is going to the house. And once the stats setback (usually around bed time, when the fire is almost out), nothing gets drawn from storage for a couple of hours or whatever. Once I program the stats, it just does it. Don't have to think about it. You might have to have the emitter horsepower to do that suitably though - another good reason to have over sized heat distribution, it allows you to setback if you want without screaming hot supply temps to recover. (Mine recovers very well with 160 supply).

I think sort of an 'ideal' baseline or guideline might be to have enough storage, that would hold an entire firebox of heat when depleted.

Guess that was more than a couple....

 

[Fred61]

An oversized boiler can and will be a bigger nightmare than an undersized one. I would steer clear of it and keep shopping.

 

[maple1]

Here's a good reference for calculations. Theses will come in handy later.

http://www.plumbingperspective.com/key-water-heating-charts/

BTU= (#gal x 8.3 x (delta T))

BTU= (820 x 8.3 x (190-160))
BTU= 204,180

BTU= (820 x 8.3 x (190-150))
BTU= 272,240

More to follow.

There is another skewing factor at play here too in the number running.

Usually when you re-charge, you do it when your supply temps get too low.

But assuming stratification is at work (I think it is with open storage & coils also), those temps are at the very top of storage.

The temps then below that will be a lot lower. I have minimum 20°dT in my storage when I recharge, most times it is in the 30 area. (I see 40 sometimes when drawing - good emitters & low flows widen that spread). Which actually applies to almost the whole storage volume, if you time things right, when the stratification layer is at or close to the top. So the above 150 example assumes an entire tank at 150 - whereas another 20 lower might be more realistic for calcing.

EDIT: I think I would try running numbers back the other way. Just for fun, you know. Start with a heat loss calc (which might be more of a guess than anything), then how long you would like to go between burns, and see how much storage you would need. That might govern things more than anything. Then you could see how that lines up with a given boiler capacity, and how many hours you would actually want to have a fire going.

 

[Bad LP]

An oversized boiler can and will be a bigger nightmare than an undersized one. I would steer clear of it and keep shopping.

This is exactly my thought. It will only get more expensive to do it twice.

 

[Marshy]

I'm not committed to that 300k boiler. It happened to be reasonably priced, local, and a gassification boiler, that's why I mentioned it. I plan to keep looking for something more appropriate but I need to do some better estimating of what my heat loads are to know what I should be looking at. The only exception might be the storage. The price seems very reasonable and buying new is not in my budget. I could install the 820 gal tank and expand later if necessary. I'd like to keep the system at 7K or less. At one point I even thought about building my own boiler but I just don't have the time.

Thanks for all the input, I have a lot of reading to do. Any links on where I should start eating the elephant would be appreciated. Right now I'm going to play around with some free online heat load calcs to try and estimate my heating demand.

 

[Marshy]

Marshy, that would suggest that the 820 tank could store about one hour's output from the big Econoburn. I recommend you either look for much larger thermal storage or (better) a smaller boiler.

Also, no need to have separate input and output coils in the tank, one coil can do both. PM me or email me at [email protected] if you'd like me to send a schematic.

Chris, you guys have some excellent products. I'd love to be able to afford a Froling boiler with lambda control.
Yes I realize I only need one heat exchanger but I wanted to do a closed glycol boiler loop so if I lose power or go away for the weekend I can flip on the oil fired boiler that's already installed. I'll be in touch I'm sure. Thanks.

 

[S.Whiplash]

Man, that Econoburn is about 1/3 of it's retail price. "IF" it's in good shape I would take the saving and purchase 2 or 3 1,0000 gal. propane tanks and insulate the hell out of them, in the end you would have a very good system at a low cost with enough thermal storage to last you a couple of days depending on your heat-loss. I doubt you're going to find anything new for under 7K.

 

[Marshy]

Man, that Econoburn is about 1/3 of it's retail price. "IF" it's in good shape I would take the saving and purchase 2 or 3 1,0000 gal. propane tanks and insulate the hell out of them, in the end you would have a very good system at a low cost with enough thermal storage to last you a couple of days depending on your heat-loss. I doubt you're going to find anything new for under 7K.

No, there's no possible way I'll get a decent boiler and storage under 7k. Actually, if I paid asking price for the boiler and the 820gal storage I would only be at $6300. If I did use the boiler I was hoping I could make up the $300 between it or the storage tank and be in it for 6K. I have about 150ft distance to where it would be placed and if the piping is $8.50/ft that'll add $1275. Only other major cost is the other htx and the glycol.

Btw, since I have a ranch style house with an unfinished basement I would likely add some pex under the main floor for radiant heat in case my base board emitters are not enough.

 

[maple1]

For some reason I was thinking the boiler would be in your basement.

(Any way it could be?)

That 150' spacing will indeed be quite a contributor to your budget with 'proper' underground piping. And 'proper' is pretty well a necessity when it comes to that stuff. I think glycol can be pricey too.

Have you looked around where you are for used LP tanks? I (luckily) found tons of them at a large scrap yard an hour away from me. I got 2 x 330's, and a 110 for expansion, for around $800. Then again, they don't go into tight basement spaces very well. 110's are pretty easy to handle, could stack & plumb a few together maybe?

Some have built their own open storage enclosure/tank themselves, in place, then used a pro custom liner from Tom. Maybe another consideration?

 

[Marshy]

I want to get the wood and fire out of the house, my wife and daughter have allergies. I have a 12x15 tool shed that I can turn into a boiler she'd. My idea was to get an indoor type boiler and install it in the shed with future plans on attaching a 24x32 ish sized garage. I might only enclose a portion of that footprint though and would like in for heat.

 

[gfirkus]

No, there's no possible way I'll get a decent boiler and storage under 7k. Actually, if I paid asking price for the boiler and the 820gal storage I would only be at $6300. If I did use the boiler I was hoping I could make up the $300 between it or the storage tank and be in it for 6K. I have about 150ft distance to where it would be placed and if the piping is $8.50/ft that'll add $1275. Only other major cost is the other htx and the glycol.

Btw, since I have a ranch style house with an unfinished basement I would likely add some pex under the main floor for radiant heat in case my base board emitters are not enough.

So, I kept all receipts and a mental note of where my cost was at. After I went over my estimate, I threw all my receipts out because I didn't even want to know. I just smile now when anyone asks me the total cost. ( I also had to get water from local city because my well water test was not good- added expense)