Oil Furnace with Storage?

[hiker88]

I'm planning on converting my home to an IWB boiler within the next two years. As you all know, the capitol outlay on these projects are one of the major drawbacks. I'd like to build this system in stages to avoid any financing of the project. I've been working with a local company that has been in the boiler business for many years and I'd like to run one of their proposals by the group here to see if it makes sense.

A major decision I need to make about my storage is pressurized vs. non pressurized. I have baseboard heat so I thought I would lean towards a pressurized system. The company in question tends to opt for non pressurized storage, but will do either.

I'm hoping to do as much work as I can on my own. This company sells a kit and plans for a non pressurized storage tank. Here is what my designer suggested and I want to see what others think.

He suggests I get the storage tank build it on my own and then connect it to my oil burner for the time being. He says that we can locate the temperature sensor high enough in the tank so that the tank can work similar to a boiler mate and then I can treat it as it's own zone and re program my oil burner aquastat for "cold start". This sounds pretty similar to what my oil company tried to sell me a couple years ago when I had them out to explore efficiency options (before I learned about boilers).

Then in a year or so when I have saved enough for my boiler, I can add it to the system and have it assume primary heating responsibilities. What does everyone think?

 

[maple1]

Are you keeping your existing oil unit, when all is said and done? (ie. after you get your IWB in).

Does it have a DHW coil? Is it capable of running in cold start mode? Most oil units like to be kept warm all the time - unless it's something quite new.

I'm not seeing any advantage to running storage with just an oil burner - I think there will be decreased efficiencies from increased stand-by losses with the added water volume.

Initial thoughts...

 

[hiker88]

I will be keeping the oil burner as a back up system. I am pretty confident that my oil burner can be configured for cold start. I had my oil company out that installed it a year or so ago and they recomended at I install a boiler mate (60 gallons I think) a temperature reset probe for outside the house, and reprogram the aqua - stat for cold start.

 

[maple1]

So you would be using the storage tank in the interim as a DHW indirect tank? What is your existing DHW setup?

That might be OK, but I'd expect some inefficiencies from stand by heat loss - might be able to minimize those some by insulating the bejeebers out of it.

 

[hiker88]

Right now, I have the worst setup possible. I just have the oil burner with its internal capacity. In the summer, you turn on the hot water to wash your hands and the boiler can run for 10 minutes depeding on how long it's been sitting since the last cycle.

The tank they sell has a very high R value. I think it was R 30 or higher - maybe a bit more than that. I can't remember exactly, but it was pretty close to the claimed values of other non pressurized storage systems I looked at online.

 

[Clarkbug]

In general, it would be a wise idea to keep your stored energy in oil instead of transferring it into the water storage which will have some heat loss, no matter how good the tanks are. Once you convert those BTUs from their state in the oil to the energy in the water, you start to lose it.

However, if I see what you are saying, it would be to install the storage tank, and then also install the DHW coil into that tank that you would intend to use with the wood boiler setup. You will see some incremental increases in efficiency due to the reduced cycle time of your OB, but depending on how old that is, those might be taken up with the heat loss.

My thought would be to build the storage tank, and get your Hx put in there that you want to use, but dont hook it up or flood the tank. Do that once you have the money to put in the boiler. I personally dont see the advantage to hooking your storage up to oil right now. Those here with much more experience than me may prove me wrong, so take my thoughts with a grain or two of salt.

 

[maple1]

I am in a similar situation in that I rely on my oil boiler, and it's DHW internal coil, for DHW in the summer when the wood fire is not on. Yes, it is quite inefficient having to keep the OB hot all summer even if next to no DHW is being used - with mine, if I did let the OB cool off, it would leak water from more than one place. I'm pretty sure I could not gain much in efficiency, without replacing my OB, or keeping a wood fire on all summer. I am also planning a system overhaul for next summer - it will include replacing my current furnace. I think if my current OB would handle cold starting, and I would not be needing or installing a WB for a couple of years, I would just get an indirect DHW tank (maybe a Superstore) and plumb it in as a separate zone. Then you would at least have the DHW side of the equation handled when WB/Storage came into play, and be able to eliminate an exchanger - and reduce your oil consumption. You could also get the storage tank ready to go if you wanted to spread the expense out. I would also consider just putting in an electric hot water tank, and turning the boiler off all together - that would depend on electric rates & usage. You could heat that from storage, when the storage & WB is in place, with a sidearm HX. So I guess along with your scenario, that would make a couple more to consider. Then again you could maybe go one further & just get a heat pump water heater, and hook it up to your existing coils. I think the OB would act as heat storage in that case. Lots of options - sometimes too many.

 

[hobbyheater]

I'm planning on converting my home to an IWB boiler within the next two years. As you all know, the capitol outlay on these projects are one of the major drawbacks. [/quote]

When my backup was oil it charged a 1000 gallon storage tank, with a open ended expansion tank higher in the building - producing 2 -3 lbs psi at the boiler.
The oil boiler was cast iron weighing 295 lbs and holding around 3 1/2 gallons of water, but had a tank less coil for domestic supply.
I attached a Hobbs meter to the oil burner and drew no domestic water or house heat for a 24 hour period and found that the burner ran for 3 1/2 hours just to maintain standby temperature. When heating the storage tank, the oil boiler would fire when the storage tank dropped to 140 degrees and would shut off at 185 and would run for 3 hours 3-4 times weekly giving me better than 50% savings.
In this system, the wood boiler, oil boiler and storage all shared the same water, but both boilers had separate feeds to the storage tank and once the boilers had finished firing, the water could not circulate between the tank and boilers.

Allan