Pressurized verse Unpressurized Storage

[kopeck]

First off I tried searching for thread, I'm sure this has been discussed before.

Anyway, I'm in the process of figuring out what direction I want to go in adding wood heat to my house.

I've got two boilers in mind, either a Scandtec Solo or a Tarm Solo Innova. I know I can get some others cheaper but the local outfit carries these models and both the brands and the reseller have good reputations.

At first I was going to try and make a go of it with out storage (which would have limited me to the Scandtec) and then add storage later on down the road. I've sort of back tracked on that now and I think I'm going to just try and get the plumbing done in one shot.

So that leads me to my question, pressurized or unpressurized storage and what the advantages of one over the other?

I think the big one that I can see is generally pressurized is going to be cheaper, especially if you can source used tanks. You do have the hassle of converting them and dealing with expansion though. I've been looking for tanks locally just to see what's out there and used is close to impossible to get your hands on. Everyone would happily sell me a new one though!

Unpressurized seems to leave you with more options (solar, easier to add domestic hot water, etc) but the cost is more.

What else am I missing?

Thanks,

K

 

[flyingcow]

I had the same question when i started. Because I planned on using my tank year round, unpressurized was a better option. Also, I wanted to put my tank in my basement, the tank i have now fits down the stairs very easily. Have been very happy with it. I also have an Innova.

But i drive a truck for a living and I've relied on thers for info. This site has given me good advice. Good Luck.

 

[afblue]

I have searched up and down on this myself, and the conclusions have come down to space.

If you have the space to put and insulated pressurized storage in 500 or 1000 gal storage. its seems to be the cleanest installation.

If you are trying to get tanks into your basement, and all you have is a 30" doorway like I do, unpressurized is your only choice unless you find 250gal vertical tanks.
Unpressurized storage although the copper is ridiculously expensive, its also an investment. Copper is only going to get more expensive, so if 15-20 years from now, if the system ever comes out, the copper is going to be worth i bet you exactly what you paid for it now. Rusty steel propane tanks probably not even close to what you paid for it.

Pressurized by design seems to be better, but it also comes down to the economics of it. If you can get propane tanks cheap and you have the place to put them, great. If you have to buy them new it ends up being the same price if not more than unpress. I dont know for sure but it seems like alot of states are passing regulations on propane tanks, so I am guessing its tying the hands of companies selling used tanks, thats probably why you are having a hard time finding them.

 

[Chris Hoskin]

good thread here: https://www.hearth.com/econtent/index.php/forums/viewthread/72019/P0/

 

[Adios Pantalones]

There are companies selling converted tanks with the fittings installed for pressurized. If you have an indirect for DHW already, then you could do this and bypass some serious money in exchangers.

 

[dpsfireman]

Another consideration, correct me if I'm wrong but the non-pressurized designs I have seen have the inlet and outlet at the top of the tank. With pressurized storage the water can come out of the bottom of the tank, go through the boiler and back into the tank at the top. The advantage to this is if there is a power or circulator failure the hot water will readily convect into the tank. This works especially well if the tanks are vertical.

 

[kopeck]

I do have a TopPerformer DHW tank on it's own zone, so I guess that is something that has to be taken into consideration.

Thanks,

K

 

[kopeck]

I guess I should also ask is sizing is any different between the two kinds of storage?

I'm look at the 30s models, so we're talking 100,000 BTU/hr units. Would 500 gallon do it? I know more it probably better, I'm just looking for a starting point.

K

 

[tom in maine]

A couple points about unpressurized tanks:
Most unpressurized tanks have inlets and outlets through the top.
This has minimal impact on stratification. I can tell you from our experience and voluminous testing done at the University of Maine and Bangor
Hydroelectric Company (they tested our smaller tanks for off-peak electric heaters), stratification is very significant in unpressurized tanks that are 4' and taller.

We are now using a 200F continuous temperature liner in most of our tanks. As soon as the old inventory is gone, all our tanks will use it. It is a proprietary
polymer that we have been testing for years, which is used in industrial applications that are more severe than hot water.

If you are paying for someone to install, insulate (to R-30) and install the large expansion tanks required for pressure systems, the gap between the two systems is not as significant as some might feel. And there will be no smashed toes or welding. :coolsmile:

As someone already mentioned, serviceability of an unpressurized tank, whether it is to retrofit for solar or move the tank around, is a relatively simple process. You can install a new heat exchanger for most applications in under an hour.

 

[kopeck]

Thanks Tom.

The one thing that I was wondering about was temperatures. I have baseboard heat, which I know like hot water (180ish) and that unpressurized didn't like to go that high. I'm assuming then that these new liners could hit 180/190 and be fine with my baseboard.

I like the simplicity of the unpressurized setup, I also like the foot print. Obviously price is always an issue but it will be interesting to crunch the numbers when you take into account either a new LP tank or one that's already fabed up and then you add insulation.

K

 

[Singed Eyebrows]

First off I tried searching for thread, I'm sure this has been discussed before.

Anyway, I'm in the process of figuring out what direction I want to go in adding wood heat to my house.



What else am I missing?

Thanks,

K

Chemicals with non pressure storage. I personally like the simplicity of a large vertical pressure tank used with a tank charger. There is no way you could get any air pockets or bleeding issues with a single tank 2 feet from the boiler like mine. Good luck, those are good boilers you are considering, Randy

 

[tom in maine]

We almost never use chemicals in any of our tanks. The only time they are used is if we are running a ferrous metal boiler directly into the tank.
With a copper heat exchanger as a boiler interface with the tank and heating system, there is no treatment required.

If I get a chance tomorrow, I will post a photo of a 23 year old liner that we recently took out. I replaced the tank with a Heat Bank in order to get the liner. I wanted to have it for show and tell. It looks like the day it went in, except that someone replaced a bronze pump that was pumping tank water into a pool heat exchanger with a cast iron pump. The water was clear, but the liner turned slightly amber. It was originally clear.
Other than that, it was like the day it went in. In our case, the liner would deteriorate by becoming brittle.

 

[SteveJ]

Another potential issue is the pump requirements based on what heat exchangers you use with unpressurized tanks.

Basically, the pressurized solutions require no circulator modification but the unpressurized will require the gpm and head of the heat exchangers involved. However, you don't have the 25psi missile in your basement or garage

 

[tom in maine]

HX pressure drop can be an issue. It is a minor one if they are properly designed.

 

[foamit up]

I believe i know where a few used propane tanks are in Maine. What size do you need?