Storage sizing calculations because of Craigs List tank deal(pics)

[infinitymike]

I'm leaning towards hooking up storage.
i was looking on Craigs List and found these tanks.

Used approximately 400 gallon horizontal or vertical T-304 stainless steel storage tank. 34" diameter X 92" long straight side. Flat heads. One end (2) 6" flanges and (1) 2" drain. Mounted on short saddles. Top fittings1) 2" fill. FOB: NC

(broken link removed to http://images.craigslist.org/5Z15W65P43k53m83laba7dd69a719f1d41a58.jpg)

(broken link removed to http://images.craigslist.org/5O65T05R53n63p23l9ba7cdaa09ad4b8d1492.jpg)

(broken link removed to http://images.craigslist.org/5O15X25R13n73kf3ocba760f1244d9dc81ae4.jpg)


They are asking $500 each.

I think its a great deal.

I dont know if I need one or two tanks.

My house is basically an "L" ranch that had 2 bedrooms and a bath dormered into a second floor over the back "L" area.
The first floor is about 1500sf and the second is about 600 sf.

I have 2 zones with baseboard heat.

I'm slowly renovating so I have:
Almost all new Andersen windows.
R38 in attic of second floor.
R15 in most of the walls.
R38 in attic over first floor.
I live on Long Island.
I would like to possible burn to heat DHW in summer and who knows maybe heat the pool.
For now I'll keep it simple and use it for the shoulder seasons and DHW.

Whatta ya guys got?!

 

[jebatty]

From the pix I'm not sure that these are pressure tanks, so make sure they meet your needs. All the pressure tanks I have seen have bulged out rounded ends.

 

[PassionForFire&Water]

Correct, they are not pressure tanks.
You can weld a 2"x0.25" cross in regular steel on the flat part. Use SS 309 welding wire if the tanks are SS 304. use 316 wire if they are SS 316
This would increase the pressure rating.
I would use them in the horizontal position, not vertical.
Looking at the nameplate on the tank in one of the pictures tells me they were used in the horizontal position.

 

[infinitymike]

Thanks guys,

I didn't think they were pressurizable (if thats even a word).
But I like the suggestion of beefing up the ends.

I only have room to lay them horizontally any way.

What do ya think about sizing?

400 or 800?

 

[jebatty]

I'm sure others know a lot more about pressure tanks than I do, but I suggest you be careful in using non-pressurized tanks in a pressurized application.

 

[Gasifier]

Mike,

This is just my opinion. And compared to most of the guys on here, I don't know squat! But I would find a pressure tank. One with an ASME stamp welded on it. It may take you a while. But if you look around you will find one. (Ebay, craigslist, used equipment companies.) It will not slow your install down at all. All you have to do is have your boiler guy put two ball shut-off valves in with a short section of pipe coming off of it. One for your supply to tank and one for your return. Then you can add it in any time you are ready. Former air pressure tanks are usually nice and clean. Have a good one.

 

[Jim K in PA]

Mike - as to your primary question (how much storage), this always comes down to what is your peak heat loss? More storage is better, to a point. More storage decreases idle time for the woodgun, and increases dwell time between burns. Only the math can tell you what is "enough". At that price, I wouldn't hesitate to get two tanks, perhaps three if you have room for them.

Others have wisely pointed out that using a non-pressure rated tank in a pressurized system is a bad idea. IMO, stainless tanks are less forgiving than mild steel due to inherent brittleness of the SS (depending on alloy). HOWEVER - you can seperate the storage from the pressurized system via a heat exchanger. You will have a more complex pumping and control schema, and you will lose some transfer efficiency through the HX, but it will certainly allow you to leave the tanks unpressurized.

 

[stee6043]

Here is some quick and dirty math to illustrate the "how much" topic:

It takes 1 BTU to raise one pound of water one degree F. For rough approximations lets say a water to air HX has a useable temp range of 40 degrees (140-180).

Soooo...for easy math. 1000 gallons x 8.4 lbs per gallon = 8,400 lbs. If you have 40 useable heating degrees in that tank that is 8,400x40 = 336,000 useable BTU's on a fully charged tank (180 top to bottom).

So take your estimated average heat load (not max heat load) and divide 336k by that number. Presto - that's how long you can heat from storage with no fire. For most newer homes (2000 and newer?) less than 4,000 square feet I would imagine (very rough guess here) that most will end up between 20,000-30,000 btu/hr average load. 20k=nearly 17 hours of heat in a 1,000 gallon tank. 30k= closer to 11 hours.

The above math is almost exactly my setup. I can usually heat for 16 hours from my tanks. Closer to 8-10 hours on REALLY cold days (below zero all day) which we have a few of each year.