Flush and Fill for Boiler with Storage

OffGridICF

Hi,

Thanks to all for sharing so much great info. After poking around I know more about water quality but one question remains.

Is it possible to clean a new system containing 850 gallons of water without breaking the bank?

My system will be based on a Froling wood-fired boiler with about 850 gallons of water for heat storage. The idea of buying 16 gallons of system cleaner, circulating it for a day or two then flushing it out is scaring my wallet. Are there any other options?

The fill water will come from a well with TDS of about 140ppm or 8.3 grains/gal. The conductivity is about 280uS/cm. If necessary, a mixed bed resin can be used to filter some of the water reducing the TDS number for the final fill. I still need to check the pH.

The storage tanks are repurposed propane tanks with some rust in them. They have been descaled and power washed but I'm sure more rust will shake loose. The boiler plumbing is a combination of black iron pipe (some with a little residual machine oil) and copper. There is a dirt-mag on the boiler return. It is a closed system using barrier PEX, an air eliminator and diaphragm-type expansion tank.

I'm making steady progress on the plumbing so any advice on how to commission the system will be greatly appreciated.

EdTheHeaterMan

I am no water expert, but I have installed hundreds of boilers over the years and I have never needed to clean the cutting oil from the cast iron sections or iron pipes and fittings. I have used untreated well water in my own boiler. I have installed boilers in many different municipal water supplied systems, and in many rural places that have different and varied well water.

If I notice that the water has caused the old boiler and system parts to fail, then I would test that water and add or subtract what was recommended to get that water to be less abrasive to the system. That was rare though.

My take is to flush the tanks as good as you can with water pressure and let any loose stuff drain out the bottom. If you do not have bottom tapings then you may need to use a vacuum to suck all that crap out with a wet shop vac. But I would not go crazy. Once that closed system water does its little bit of damage, that water will become inert with no more corrosiveness left to do any more damage. Just don't be adding more new water on a regular basis. Then check and flush the dirt mag with a little additional water as possible. (if a gallon of flushing renders clear water, then don't use 5 gallons to do the flush)

That is my take on this subject. @hot_rod may have other ideas, he deals with water across the world, not just the water in my back yard.

hot_rod

Does Froling have a water quality spec?

Years ago we used TSP for boiler cleaning

Many have used dishwasher soap.

OffGridICF

Thanks Ed,

It sounds like flushing the system with well water then using the well water passed through a DI mixed resin filter for the final fill should be adequate. I can monitor the TDS / conductivity and pH during that process. The bigger concern was flushing out any residual cutting oil, flux, etc. but it sounds like that hasn't been an issue for you.

Most of the crud should already be out of the tanks after pressure washing with Simple Green followed by a good rinse prior to welding on the new fittings. They got another pressure washing right before installation. They are standing vertically with air vents up top and drains at the bottom so any additional crud that settles out can be easily drained. There are 4 tanks in series - not ideal but the price was right.

Thanks Bob,

I'll consider the dishwasher soap option if a bunch of stuff shows up in the dirt-mag.

The US version of the Froling docs that came with the boiler say hardness < 100ppm and pH between 8.0 and 8.6. They also spec chlorine at <30mg/L which should not be a problem since the well water is not chlorinated.

In the European version of the Froling manual there are different specs depending on the country. Germany allows total hardness up to 200ppm while Switzerland only allows 10ppm. Both spec conductivity at <100uS/cm.

To make it even more interesting, in Germany fill water must conform to VDI2035 which specifies hardness based on the total water volume / boiler rating. For my system, the volume is about 3218L and the rating is 30kW which gives 107L/kW. In that case, they specify a hardness of 0.02mol/m^3 which works out to a stunning 2ppm CaCO3. Perhaps more water provides more potential for scale formation so it needs have very low hardness. Their limits are based on completely refilling the system three times during its life. I'll include the VDI2035 chart from the Froling manual.

And a nice summary from https://www.heatgeek.com/heating-water-treatment-explained-vdi-2035/

Thanks again for taking time to provide your feedback.