Does this all make sense?

[canmic]

I have been working on figuring out how to convert from $$Oil$$ to wood, and solve a few problems that my current oil setup is causing. I've done a lot of reading and had some discussions and this is what I came up with. Looking for some constructive comments or pointers on anything I am getting totally wrong.

I have calculated the peak BTU demand of the house several different ways, using calculators going room by room with areas and windows and R values, adding up how much oil and electricity I used last year for heat and getting the degree days and going that route, and doing a basic rough guesstimate based on a few numbers and it always comes out to 100,000 btu/h peak demand +/- about 10%.

The existing system is big old cast iron radiators, gravity flow open system with an expansion tank in the attic. Tank is about 30 feet above boiler in basement, highest radiator is about 20 feet above boiler. Pipes are all iron and steel.

Current boiler is an old retrofitted coal burner burning oil, scary looking. Price of oil is also scary looking, likely to pass $5 a gallon this winter, even higher next winter.

My plan is this:

Put in a gasification boiler in the garage, about 120 feet from the current boiler. Bury insulated 1-1/4" double tube insulated o2 barrier pex about 3 feet down between the house and the garage. Run the boiler loop under pressure with a short bypass and a thermostatic mixing valve at the boiler to prevent thermal shock.

Replace the existing scary boiler with a big flat plate heat exchanger rated at about 120,000 btu/h. sandwitched in lots of Roxul insulation.

Put a sidearm heat exchanger onto the existing electric 100 gallon DHW tank and valve it into the boiler loop. Put a thermostatic mixing valve on the DHW tank so that the line to the house from the tank is fixed at 120 F, set it up to keep the tank at about 140 F via the boiler (or the storage) when they are hot.

When the boiler line gets to the house,have it feed 2 "side loops" for the radiator HE and the DHW HE, basically in parallel but valved with aquastats.

After the 2 side loops, run the boiler loop through a 250,000 btu/h HE in a big unpressurized "open" storage tank (insulated plywood/liner type tank, polyiso insulation, marine plywood, EPDM or custom high temp plastic liner). I've sized it out and I have a perfect spot for a 4,000 gallon tank (4400 gallon total volume, leave 10% for expansion), insulated to R-30 on all sides, any heat lost would just go into the house anyway.

Then the boiler loop goes back to the boiler.

Couple of valves and a pump on a bypass of the boiler loop where it enters the house so that when the boiler isn't hot, nothing runs through the outdoor lines and the storage loops (as needed) with the DHW and radiator HEs.

Pumps and valves etc to make the water go where it needs to go when it needs to go there.

Booster pump on the gravity flow radiator lines to beef it up a touch and to compensate for the flow restriction of the HE.

For the boiler, looking for something that would run at about 250,000 btu/h and hopefully have about an 8 hour burn time at that average rate over the burn, on douglas fir. Maybe the NextGen Biomass 80 or 100? Not sure. 120k btu oil boiler in parallel with wood boiler as backup, only triggered when DHW or radiator needs heat and storage is below 140 and wood isn't burning, ignores and bypasses storage when boilers are in oil burning mode.

UPS power supply for both boilers for times when the power is out with decent sized battery bank (the power goes out for days at a time here sometimes).

I think that's about everything.

Any downside to having such big storage? I worked it out that it gives me a 24 hour cycle time with an 8 hour boiler burn on the coldest days and during the shoulder season, I can get a 48 hour cycle time most of the time, based on storage temps ranging from 140 F to 180 F (40 degree delta), assuming I got the calculations right.

Anyone know how to find data on burn times and average BTU/h of various gasification boilers based on wood species?

Does it make sense to set things up with only one HE in the storage or is it important to use 2, a "charging" one down at the bottom of the tank and a "draw from storage" one up at the top of the tank? (water in tank will be about 60" deep)

 

[maple1]

I think I read how you would get heat into your storage, but how would you get it out of there & into your house? Might be I missed something.

Sounds like you've been doing your homework - that is good. Even if something needs adjusting in your plans, that's almost trivial at this point. I'd say the main consideration right now is just the wood handling & supply part - if you're up for all that entails, I'd be doing all I could to get rid of the oil as you're planning now.

BTW, could you put a wood boiler where the oil one is rather than in another building? That would save a huge amount of work, if possible - on the system & install side at least, maybe it would introduce problems on the wood handling side. 4000 gallons is a lot of storage though, so you must have some room down there - I think you should be able to get by with a lot less if more room would help on another aspect. And, realistically, how much would you expect your backup heat source would be used? If you're home all or most of the winter, and it wouldn't be used much at all, I'd seriously consider ditching the oil all together and use an electric boiler for backup.

 

[heaterman]

Got the wood/coal grates that were in the old beast originally? Might not be a bad option.

Those old gravity systems were/are a thing of hydronic beauty when functioning right. They are very easy to screw up when you start modifying them from the way the dead men that installed it intended.

 

[rkusek]

Sounds like an interesting project. Isn't there a way to keep the old beast functioning as is, but heat it's water via a shell tube or plate HX where it would still function the way it was designed? Is pressurized storage an option in your garage? It would be much easier to maintain, simplify your plumbing, and not have the losses of another HX. Two 1000gal tanks at 185 degrees drawn down to 120 degrees would yield about 1.1 million btus per Jebatty's numbers. That would be about 11 hrs based on your 100k estimation which is hopefully just on the very cold days. Looks like you would need to burn about 400lbs. of wood (6kbtu per pound) on those days which is probably 2 loads of a 80kW class gasser.

 

[canmic]

I think I read how you would get heat into your storage, but how would you get it out of there & into your house? Might be I missed something.

I was going to use the same Hx for both, by having a short-circuit of the boiler loop with a valve to shut off the underground lines, so basically when the boilers were "off" (cold) and the water coming from them was "cold" and that pump shuts down, but there is still heat demand and the storage is hot, the valve would shut and the pump would come on and circulate the water in the loop within the house, follow me? Does that make sense or is it better to have 2 Hx in the storage, one down deep to charge it and one up top for taking the heat out and then valve the 2 of them so only one or the other is used at a time, depending on the conditions?

Sounds like you've been doing your homework - that is good. Even if something needs adjusting in your plans, that's almost trivial at this point. I'd say the main consideration right now is just the wood handling & supply part - if you're up for all that entails, I'd be doing all I could to get rid of the oil as you're planning now.

I've got 20 cords of wood piled up inside the storage barn and dried about 2 years and another 5 stacked outside from this summer and drying. The storage barn is just behind the garage and there is room to stack about a cord inside the garage where the boiler would go. Easy to just wheelbarrow wood from the barn to the garage on weekends and then take from the stacked cord in the garage. I get about 5 cords a year for free now with only the effort of splitting and stacking it. Worst case, I can get a cord of doug fir delivered for $220 here, $250 delivered and stacked.

BTW, could you put a wood boiler where the oil one is rather than in another building? That would save a huge amount of work, if possible - on the system & install side at least, maybe it would introduce problems on the wood handling side. 4000 gallons is a lot of storage though, so you must have some room down there - I think you should be able to get by with a lot less if more room would help on another aspect. And, realistically, how much would you expect your backup heat source would be used? If you're home all or most of the winter, and it wouldn't be used much at all, I'd seriously consider ditching the oil all together and use an electric boiler for backup.

The storage barn is about 200 feet from the house, the garage is next to it (120 feet from the boiler to the old boiler for the pipes). The boiler would be in the basement with a small indoor staircase to carry wood up and down. The old chimney is unlined brick and there is just a single flu available. The ceiling height in the basement is about 74". If I was going to put the boiler in the basement, I'd need a wood/oil combo boiler with about 250 btu/h output from the wood and 120 btu/h output from the oil, that can fit in a space with that low a ceiling. Can't find such a solution. Can't use 2 boilers in 1 flu, would have to line the chimney and makes some curves and is about 50' long. Also oil tank is in the basement and insurance isn't happy about that, nor about the boiler inside the house.

As far as the backup goes, we go away in the winter 2 or 3 times for 2 weeks each time and the power is known to go out here for 4-5 days at a time every other year and for 48 hours at least once a year in the winter.

The water storage is in a crawlspace next to but walled off from the basement section where the boiler is. Access is from outside through a hatch on the veranda. I can drill holes to run the pipes through but it wouldn't be a practical location for wood storage or for boiler location (no way to run a chimney).

 

[canmic]

Got the wood/coal grates that were in the old beast originally? Might not be a bad option.

Those old gravity systems were/are a thing of hydronic beauty when functioning right. They are very easy to screw up when you start modifying them from the way the dead men that installed it intended.

Thought about that but the thing is soo inefficient I'd end up burning about twice as much wood each year, plus it's a pain to get the wood into the basement where it is and there isn't much room for wood storage there. Lastly the old boiler is covered with asbestos that is starting to crack and look dangerous. Want to get rid of it asap.

Also, the conversion job done on it involved putting and oil burner into the ash drawer and filling the coal burning chamber with sand and welding the doors shut. Would not be easy to 'unconvert' it back.

Luckily I do have an old guy who works on it who is the son of the guy who put it in and apprenticed with him for many years.

 

[canmic]

Sounds like an interesting project. Isn't there a way to keep the old beast functioning as is, but heat it's water via a shell tube or plate HX where it would still function the way it was designed?

That is "stage 1" of what I am planning. But the wife and the insurance company want it gone. Also there is the asbestos issue and the indoor oil tank issue.

Is pressurized storage an option in your garage? It would be much easier to maintain, simplify your plumbing, and not have the losses of another HX. Two 1000gal tanks at 185 degrees drawn down to 120 degrees would yield about 1.1 million btus per Jebatty's numbers. That would be about 11 hrs based on your 100k estimation which is hopefully just on the very cold days.

Don't have room for 2 x 1000 gallons in the garage, would have to build another building for them next to it. Also with such a long run to the house, there would be a lot of loss (about 6000 btu/h) in the pipes and the storage tank losses as well. With the unpressurized storage under the house, any losses just go up into the floor of part of the house, so they aren't truely losses.

No "losses" from the storage Hx, where would the heat be "lost" to?

I can't go down to 120 for the storage, as the radiators won't really function below about 140, I'm in the process of figuring out how low they can function by dialing down the aquastat on the existing system temporarily to check. Also I figure a degree of loss in the pipes plus another 4 of unbalance in the Hx so storage in the garage side would have to be about 145 minimum to work.

I had thought about a garn but I am reluctant to go that way due to the same reasons, need a new building, outdoor storage losses and about 10 times the heat loss through the underground pipes due to them being flowing 10 times as long.

Looks like you would need to burn about 400lbs. of wood (6kbtu per pound) on those days which is probably 2 loads of a 80kW class gasser.

The wood I have available is Doug Fir, which from what I can find out is about 26 mbtu/cord, also from what I can find out, the ratings of the boilers are based on about 30 mbtu/cord type wood so I figured I'd need to go with about a 100 kW boiler for the wood boiler to be on the safe side. The cost difference between 80 and 100 isn't much, given the total cost involved of putting the system in. Any recommendations about which boiler?

 

[Eric Johnson]

I had a gravity feed system like the one you describe with an old coal to oil conversion. All I did was put in a stainless steel chimney liner and replace the old cast iron boiler with a new, combination wood/oil unit. No pumps. No heat exchangers.

If I were you, I'd put a gasification boiler in to replace the current oil unit and call it good. You can use a pump to circulate domestic hot water through a tankless coil in the new boiler, or use a sidearm with no pump involved. Either way would work great. BTW, I use my EKO 60 (205K BTU) without storage and it works just fine. My house is full of cast iron radiators, so there's some buffer and storage already built in.

If you still want a remote installation, I'd keep the existing boiler vessel and just pipe the hot water into it and let the existing gravity feed system do its thing. As Heaterman says, those things are really a marvel of engineering and simplicity--if you resist the temptation to screw them up with pumps, zones, etc. It was designed (yes, by dead men) to heat your house. Let it.

 

[canmic]

I had a gravity feed system like the one you describe with an old coal to oil conversion. All I did was put in a stainless steel chimney liner and replace the old cast iron boiler with a new, combination wood/oil unit. No pumps. No heat exchangers.

Can't find one that I can install with such a low height clearance. This was my first idea before the height issue came up. I would have to put a short loop with a pump and a mixer valve to prevent thermal shock though as the cold water that comes back would overwhelm the volume in most modern boilers.

If I had the height, or if someone made a short enough unit, this would probably be the way I'd go. Any ideas on a short 200k btu unit?

The other issue is getting it in there. I would have to get it down a narrow staircase and through a 36" doorway. I can't imagine how to do that with something that weighs over 2000 lbs.

If you still want a remote installation, I'd keep the existing boiler vessel and just pipe the hot water into it and let the existing gravity feed system do its thing. As Heaterman says, those things are really a marvel of engineering and simplicity--if you resist the temptation to screw them up with pumps, zones, etc. It was designed (yes, by dead men) to heat your house. Let it.

That is basically phase I, but using a Hx on a spare set of in/out pipes on the existing boiler with a little pump to circulate that mini-loop. Then the existing is my oil backup.

If the old one wasn't covered in asbestos, I'd probably leave it in place and use it as a mini storage tank and distribution system. It works.

I will look into what would be involved to get rid of the asbestos but leave the old boiler in place. That way the distribution system would remain as is and as has worked well for 100 years. I can always build a plywood box around it and wrap the thing in Roxul batts or spray in high temp foam insulation to take the place of the asbestos. Maybe if I did that, I wouldn't have to worry about removing the asbestos as the foam would "seal it in" safely.

 

[Eric Johnson]

Mine was festooned with asbestos, too. But in New York, homeowners can do the removal themselves and put the stuff out with the trash for regular pickup. Don't try that if you're a professional of any kind (plumber, heating contractor, etc.) or you'll wind up in prison. Funny how these things work. Sealing it up with plywood and/or foam is probably an even better idea. Put the new boiler somewhere where you have the headroom and just pipe a loop into the existing unit, either direct or with a flat plate hx. As you said, it's been working just fine for 100 years.

I had about 7 feet of headroom to work with, so boiler height wasn't an issue, though I find it hard to believe that you wouldn't have room for a replacement, but you're there and I'm not. As to the return, I didn't do anything about that on mine (didn't know I needed to) and the boiler rusted out (at the return) after 8 years. What I'd do now is put a heat exchanger jacket around the gravity return and pump hot water from the top of the boiler through it. I think the convection is slow enough so that the return water would get warm enough, and then there's no concern about volume. Or, strap an electric heating element to the pipe for the same effect and probably minimal additional cost on your electric bill.

I guess what I'm getting at (and you seem to appreciate and agree) is minimal disruption to a heating system that works--just another source of hot water, which is what you'd get with a separate boiler--wherever you decide to put it. And hey, if that oil burner still works, you've got a built-in backup with no additional expense.

 

[canmic]

Mine was festooned with asbestos, too. But in New York, homeowners can do the removal themselves and put the stuff out with the trash for regular pickup. Don't try that if you're a professional of any kind (plumber, heating contractor, etc.) or you'll wind up in prison. Funny how these things work. Sealing it up with plywood and/or foam is probably an even better idea. Put the new boiler somewhere where you have the headroom and just pipe a loop into the existing unit, either direct or with a flat plate hx. As you said, it's been working just fine for 100 years.

I had about 7 feet of headroom to work with, so boiler height wasn't an issue, though I find it hard to believe that you wouldn't have room for a replacement, but you're there and I'm not. As to the return, I didn't do anything about that on mine (didn't know I needed to) and the boiler rusted out (at the return) after 8 years. What I'd do now is put a heat exchanger jacket around the gravity return and pump hot water from the top of the boiler through it. I think the convection is slow enough so that the return water would get warm enough, and then there's no concern about volume. Or, strap an electric heating element to the pipe for the same effect and probably minimal additional cost on your electric bill.

I guess what I'm getting at (and you seem to appreciate and agree) is minimal disruption to a heating system that works--just another source of hot water, which is what you'd get with a separate boiler--wherever you decide to put it. And hey, if that oil burner still works, you've got a built-in backup with no additional expense.

For the height issue, I'm thinking of the nextgen biomass 80 or 100, and those are 72.6" high. My floor joists above are at about 76" high, there are a few big issues if I try to wedge something in that tight, such as trying to sort out the 2" steel piping on top and also I'm sure there is some sort of a clearance requirement to combustibles like wooden floor joists. The old boiler is a short fat thing only about 48" high and even with that, the piping is a bit "creative"

And also there is the issue of getting it in there without ripping out a foundation wall, not gonna happen. If they disassembled and then reassembled, that would make it easier but I'd still have the height issue.

I am really liking the idea of putting spray foam around the old boiler in some sort of wooden box to cover the asbestos and then using it as a small storage tank and distribution system, if it ain't broke...

I think that a flat plate HX makes the most sense for connecting the two systems, that way I could keep the water separate, run the boiler a bit hotter than the rads for efficiency, get a decent flow rate for the boiler loop (again for efficiency) without mucking with the gravity feed or cavitation issues.

When you say the boiler rusted out, you mean the new boiler rusted out where the cold water was hitting the return? Or did you mean the old boiler and it was the return from the radiators? If it was the old boiler, I think putting a small Hx jacket on the boiler loop there would be easiest solution if it was the new boiler, that's why I was going to put a short circuit loop with a thermostatic mixing valve in, to keep the return temp on the wood boiler at 140 F to avoid thermal shock and condensation corrosion issues. Makes sense?

I am really liking this idea because it means that I can phase things in over time. I can start by insulating the old boiler and sealing in the asbestos, then I can put the wood boiler in the garage and run the insulated PEX to the old boiler and put in a Hx linking to the old boiler. Then later I can add in DHW and some heat storage. Nice to put things in one step at a time.

What I'm wondering about is hooking the Hx into the old boiler. What would be the best way to do that? I'm thinking of this sort of set up:

T off of Return Line from Rads -> small bronze pump -> Hx -> T off of hot water line back to rads

So basically the Hx is in parallel with the old boiler, with a small pump to push the water through the Hx

Alternately, I could grab one of the return lines entirely, not a T and put the pump then the Hx then into the boiler, might be better as this would pump the hot water into the boiler and pull a bit on the return line and would deal with the fact that there are multiple ins and outs to the boiler. I don't want to muck up the gravity flow.

Thoughts?

 

[canmic]

Ok, I'm going to take a totally new approach here. I have to redefine the word "difficult" and accept that sometimes you just have to say "But why not?"

I talked to a construction working friend and he said "Can't find a short boiler and can't raise the ceiling? Lower the floor! If height is such a big problem, bust out the floor, dig a hole and then re-concrete the floor with a bit of a down-slope into a flat lower area that is big enough for the boiler and to be able to walk around it and stand in front to load etc. He said he can accomplish this no problem for me for a reasonable cost (a lot less than running insulated pex out to the workshop!)

This solves a lot of my problems!

So, what I'm thinking now is:

1 - Leave the old boiler in place, cover it with isocyanurate spray foam (rated to 240 F) to solve the asbestos problem. Use it as the backup oil boiler for now.

2 - Pump the hot water with a small pump through 2" pipe into an unused (capped off) hot water outlet on the old boiler.

3 - Attach the return line of the new boiler to an unused (capped off) return line on the old boiler, making basically a very low pressure loop.

4 - Do all of the proper near piping for the new boiler like an aquastat feedback loop to keep the return temp at 120 like the boiler wants.

5 - Add a big iron radiator directly over the new boiler on the 1st floor above and T it in to provide the emergency gravity feed heat dump in case of pump failure (with the appropriate valves and such). Can even have a parallel Y piping for it on the feed line with a thermostat controlled valve so that rad can heat the room as well if that room is cold.

Then later...

6 - T in another low pressure loop that goes out to the HX in the unpressurized storage tank and back with its own pump. Valve and control that loop and pump so that if the heating system is hot and the boiler still has heat, off to storage it goes and if the heating system needs heat and the boiler isn't burning, pull from storage.


Everything is short runs, so nice big pipes.

Anything I"m missing or totally getting wrong?

Thanks for any comments!!