tank and system sizing help

[Hamilton]

Dear all, I've been reading up on boiler systems for six months now (largely on this very helpful forum), and am just about ready to take the plunge.
I've settled on a Frohling system, and was going for a 40/50. The house is about 4,200 sqft, and reasonably tight (mid-'80s, so oil-crisis thinking).
In addition to keeping me toasty warm and helping out the environment, one of the main aims of the system is to keep the house at a safe non-freeze temperature when I'm not home - which tends to be about 4 days per week. The plan was to oversize the water tanks, so that there'd be sufficient buffer to do this effectively, with an existing relatively new buderus oil burner as backup, to kick in once the water tanks get below the temp at which they're effective. I would like the frohling to do most of the work though, for as many hours as possible whilst I'm away.
The problem is however, that the pressurized tanks that have been recommended run at $10,000 per 600 gallons of storage (tanks alone, not the boiler or pipework) - so $20,000 for our needs (providing 1,200 gallons of pressurized storage). This figure has completely blown the overall boiler project budget out of the water, and pretty much makes it a non-starter.
I've been reading that a lot of people use re-purposed LPG tanks in lieu of certified pressurized water tanks, but I wonder if anyone has any opinions on 1) using LPG tanks effectively and safely. 2) whether there are cheaper certified tanks out there. 3) whether we could achieve our goals by using larger, non-pressurized tanks (we have plenty of space in the basement). 4) any other way that the system could achieve our goals without costing $45,000 in total.
I really appreciate any insights that anyone is able to offer.
Thanks.

 

[BoiledOver]

Where are you located? I will supply you with as many tanks as you need for $10,000 each, nooo problem.

Honestly, depending on your location and heat loss calculations, I doubt that 1,200 gallons would be sufficient for a 4 day cycle. Or even 2 for that matter. Realistically for a house of that size, 2,000 gallons would be the minimum.

If you provide additional information, there are many experienced members here to assist you. Keep in mind that it is June and it will be quite slow in here until some time in September.

 

[lotawood]

I got my old 500 gallon propane tank at scrap iron prices. It was rated way beyond what my boiler can do with temperature and pressure. I just went to my propane company and said what I wanted and what is was going to used for. They even loaded it.

It is hard to make $20k for storage pencil out. I would think you could get something for 10% of that or less. You just got to search the scrap yards or ask around. I don't know up-pressurized prices, but the liner from (I think) Tom in maine is the one that gets high marks.

Your size house might be hard to get enough wood heat over four days without doubling up on storage. You also need to plan on insulating the tanks to a high r-factor.

That is a good choice for a boiler.

 

[maple1]

Exactly what tank costs $10,000?

That sounds pretty ludicrous to me.

Edit: my 660 gallons of storage cost me around $1000, including insulating material.

 

[flyingcow]

What do you heat it with now? Oil?Propane? And how much do you use in a year?

And what type of delivery system? i.e. baseboard? radiant? hot air?

 

[airlina]

Just went thru this as I am adding storage to my Econoburn 100 after 5 years of burning without. In searching my area (western NY) I found 1000 gallon tanks for $1000 and 500 gallon tanks for $200. I went with 500 gallons of storage, and total cost of tank after having fittings welded on and spray on foam was in the neighborhood of $1000. Add to this the cost of misc black pipe fitting, drain, temp wells, air vent etc to get the tank ready for install. As I type this I am filling the system to do some test firing. Winter comes early here! Bruce

 

[maple1]

To your 4 questions, from my POV:

I've been reading that a lot of people use re-purposed LPG tanks in lieu of certified pressurized water tanks, but I wonder if anyone has any opinions on

1) using LPG tanks effectively and safely.

I think the majority of posters here are doing this, some for years.

2) whether there are cheaper certified tanks out there.

Define 'certified'. And your reasons for wanting that. Have you checked out all the advertiser banner ads here? I know Smokeless Heat sells 'factory' tanks you can see on their site, but think you have to call for prices. They also have re-purposed propane tanks. (And some really nice boilers ) Other vendors may do the same thing.

3) whether we could achieve our goals by using larger, non-pressurized tanks (we have plenty of space in the basement).

Maybe - not sure of all your preferences though. Member here 'Tom In Maine' is the first guy to go to to check out that aspect - he makes & sells tanks & liners, sells custom made liners to fit your tank. Main general difference is non-pressurized will need heat exchanger(s), pressurized will need expansion tanks. Non-pressurized may also add some humidity to your space with that much of it.

4) any other way that the system could achieve our goals without costing $45,000 in total.

Mine ran me about $15k, all-in. That's for gassifying boiler, loading unit & stand, spare ceramics, 660 gallons of storage, new 80 gallon electric hot water tank, electric boiler for backup heat, freight/duty/currency hit to get the boiler here, all plumbing & control stuff, insulation, and tax on what I bought here. Basically my entire heating system, except for rads, zone valves, and chimney. Doing it all myself (except wiring the electric boiler & hot water tank).

Our 2 storey is 2700sq.ft., plus 1500 of unfinished basement. I can burn for 6 hrs. a day, and coast the other 18 on storage. But the house isn't quite as warm at the end of the 18 as at the end of the 6 - I can match the time of burn to the heat demand cycle though, so we are always comfortable. With a house that size, and 2000 gallons, you might get through 3 days and have your oil kick in for the 4th - but that would depend on how cool you don't want your house to get before you get home.

 

[Tennman]

Welcome Hamilton, With a quote like that on the storage, I'd make sure I got competitive quotes on the other major components. There are a number of boiler distributors who sell modified LP tanks for storage ready to go. I was tempted to drive up north to purchase two that were all welded up, but in the end our welder did the fab work for us. If you want more than 1,000 gal that could get difficult with LP tanks since they're in increments of 500 gal I think.

Our home is larger and less efficient than yours and our two 500 gal tanks work well. I chose to go vertical vs horizontal to save floor space and get better stratification. Many here have horizontal because of ceiling height and the horizontal guys are all happy too. So there doesn't appear to be a significant stratification advantage. I can tell you placing those tanks was "interesting" with a 10,000lb fork lift in a 10' ceiling barn. I searched Craigslist for several months to find two 500 gal tanks. Left them open/vented for ~3 months before welding and still could smell the stuff they add to propane.

I designed the tank legs and fittings and had our welder fab them up in a well equipped shop. If you don't know good welders and have equipment to handle the tanks, buy from one of the gasification boiler distributors who modify them, i.e. contact a EKO, BioMass, etc boiler distributor for tanks. Seems like I could buy modified 500 gal tanks for ~1200-1500 each ready to go without foam insulation. I didn't save lots of money doing it myself. I think I spent ~1,000 to get them sprayed with ~4" polyurethane. I welded my demand supply and return nipples at the dome to barrel tangent point. Some just use the top and bottom boiler return/supply manifolds. If I was to do it again, I'd probably split the difference and weld the nipple midway of the dome to get into a hotter zone of the tank. If you go vertical, I can provide minimum weld length and leg angle size to make sure it's safe. That's a very big deal because the combined tank/water weight approaches 5,000lbs. Obviously a tank leg or stand weld failure could kill someone.

From someone who burned without storage for 5 or 6 seasons, I really should have had storage after the first season. Big mistake not having storage early. I totally underestimated the benefit to the system and my lifestyle. BTW, I did not weld threaded fittings to my tanks. I welded 6" nipples so I do not have any threaded joints under the foam, only weld joints. In the next few months we'll be modifying the manifolds to add capability. I should have planned on many more fittings/wells for thermocouples. I'll be adding a control/monitoring system to better manage/monitor temps from top to bottom. Data acquisition/control systems are getting very cheap to run off obsolete laptops. So allow for plenty of temp sensors so you can better control/monitor in the future. Here's a pic in our boiler barn. BTW, I installed that industrial fiberglass insulation. Surprisingly inexpensive but a pain to install. Good stuff.

 

[Hamilton]

I'm bowled over by how generous you all are with your advice and shared experiences - thank you!
It seems that the proposal they've put together for us is very overpriced and still wouldn't be quite fit for purpose.
We're in north eastern Connecticut, and of course it was a pretty dreadful winter this year. We got through about $4,000 worth of heating oil, but the furnace is getting on to 30 years old and so I imagine pretty inefficient. The house is primarily forced air, with about 1,000 sq ft of under floor water-radiant as well.
It's reassuring to hear that with a properly sized storage system, we should be able to get 3-4 days of heat. We don't need the house to be toasty warm for this unoccupied period, I just don't want it to freeze.
The picture above is very useful. I think we'll have to go horizontal, as although there's plenty of space, we don't have the vertical clearance that Tennman does in his barn.
Someone also asked why I feel the need for 'certified' tanks - I don't, at all, it's just that the chap that did the quote for us said that $10,000 is what it costs for 'certified' tanks.
I really do appreciate all the input. I'll get on to Tom and some of the other distributors mentioned above.

 

[tom in maine]

Just for the record, an unpressurized tank that is sealed properly does not increase the humidity in the room it is installed in.
It a simple thing to do.

 

[Tennman]

I like to have my system pressure cold at about 10 psi and keep it under 20-23ish psi when charged. Our pressure relief is just a standard at ~30psi. So the max pressures are really nothing for the wall thickness of a 500 gal propane tank. You need to get plugged into a distributor who installs lots of systems with lots of experience. Someone like Tom above would be a good source up in your area. Crazy high quotes often come up here from inexperienced contractors who cover their risk with big dollars. Get the Froling guys to spec the components then hire a good plumber. Your research has lead you to an outstanding boiler. Never read of a frustrated or disappointed Froling customer here.

Pretty quiet around here this time of year. But now is the time to be preparing for 15-16 season. Best wishes.

Oh... and have your Froling guy do some math for you as regarding the total stored btus at say... 180F in 1000 gal. I doubt it will last 3-4 days. Except during the shoulder season, most in your latitude will burn once or twice a day.

 

[Hamilton]

I like to have my system pressure cold at about 10 psi and keep it under 20-23ish psi when charged. Our pressure relief is just a standard at ~30psi. So the max pressures are really nothing for the wall thickness of a 500 gal propane tank. You need to get plugged into a distributor who installs lots of systems with lots of experience. Someone like Tom above would be a good source up in your area. Crazy high quotes often come up here from inexperienced contractors who cover their risk with big dollars. Get the Froling guys to spec the components then hire a good plumber. Your research has lead you to an outstanding boiler. Never read of a frustrated or disappointed Froling customer here.

Pretty quiet around here this time of year. But now is the time to be preparing for 15-16 season. Best wishes.

Oh... and have your Froling guy do some math for you as regarding the total stored btus at say... 180F in 1000 gal. I doubt it will last 3-4 days. Except during the shoulder season, most in your latitude will burn once or twice a day.

Thanks Tennman. I've been speaking to Tom offline, and am thinking about un-pressurized, at 2,200 gallons. I'll speak to the dealer about sizing, but that seems more appropriate. Thanks for your help.

 

[Dutchie84]

Any updates on your install?

 

[BoiledOver]

I can tell you placing those tanks was "interesting" with a 10,000lb fork lift in a 10' ceiling barn.

LOL. Some folks take the easy way. Picture one man in a nine foot ceilinged shop, 2-500 gallon tanks needing stacked horizontal, one pair of saw horses, one engine hoist and a floor jack. Took 3 full days to get everything fitted, welded and erected. A neighbor offered to help but I wouldn't dare risk someone else's life, after all, it was my adventure. Yes I probably looked like a monkey having a football at times.