Copper DHW coil in pressurized storage

[hartkem]

Been toying with the idea of incorporating DHW into my boiler system. Have EKO 40 and waste oil burning buderus boiler in outbuilding. 500 gallons of pressurized storage in basement (one of those red preinsulated square ones new horizons sells or used to). I currently use a 40 gallon lp fired unit for DHW. I've been researching the idea of fitting one of those finned copper coil Water to water exchangers that bolt onto a boiler into my pressurized storage. I'm a fairly skilled welder and thought about removing the skin and insulation from the top of my storage and welding a custom made flange sized to one of those coils to bolt down to. I'm trying to avoid adding more pumps and this seems like a simple way to do it after the modifications are done. I would drain down the tank this summer when I'm doing some other repiping. What do you guys think?

 

[maple1]

Personally I would avoid cutting into my pressurized tank, and go with a plate HX to heat your LP tank. It would only need one more circ - I used a small B&G Ecocirc. And I guess something to control it. I used a Johnson A419.

My welding isn't 'skilled' though. But I did have some welding done on my LP tanks by a welding shop. They had to come out & touch up a couple of pinholes I found when pressure testing after I got them home. That was most likely due to getting cast fitting instead of steel - but I still would be very reluctant to cut a tank open after that episode. But some do do it with success.

 

[Bad LP]

I'm thinking about taking my DHW out of the wood boiler system and putting it back onto the System 2000. I've seen more times than not my DHW zone open trying to make 140-150 degree water with a loop temp of 120-140.

 

[maple1]

I only heat mine to 125-130 or so.

 

[hartkem]

I'm thinking about taking my DHW out of the wood boiler system and putting it back onto the System 2000. I've seen more times than not my DHW zone open trying to make 140-150 degree water with a loop temp of 120-140.

Before I added the waste oil boiler I never had the intention of heating the DHW because of your reasons mentioned above and I already have a big heat load. I heated all this winter and never burned any wood but I did go through 800 gallons of waste oil so far. My tank heated via the buderus waste oil never goes below 160. Of course if waste oil becomes less plentiful I'll be using wood again or a combination of both. I guesss I'm just trying to get an idea of how well the coil would work in my storage tank. I use about 200 gallons of propane for domestic hot water yearly.

 

[hartkem]

This is my boiler shack. The waste oil convertered EKO will be transitioned back to wood once the buderus oil boiler install is completed and the oil burner moved to it. Very clean burning with no visible smoke. The EKO convertion worked very well and it was a test really to see how viable it was to heat my house with waste oil. With how successful it was this winter I decided to install the buderus so I could fire one or both depending on available fuel source and time.

 

[Bob Rohr]

I think you would be better served and invest less $$ to use flat plate as maple 1 suggested. It would perform much better with two moving flows, be easy to service and probably perform at much lower tank temperatures.

I have a small plate on my 500 gallon tank and can take a warm shower with the tank at 120F, at a continuous draw around 1.5- 2 gpm.

Boiler tankless coils like that need fairly consistent, high boiler temp 180+ to perform well.

 

[maple1]

Boiler tankless coils like that need fairly consistent, high boiler temp 180+ to perform well.

We had one in our old boiler. In summer I would set the boiler back to maintain about 145-150. That was adequate, but barely. It didn't take much water use before the temp dropped and boiler finally kicked in. The key element was water movement in the boiler to wash hot water over the coil. Otherwise, the water immediate to the coil would be cooled off by the coil, and the hot at the taps would decrease in temps quite drastically without the controls or boiler really knowing it. With the plate I can maintain our electric tank water heater with supply temps down to 130 or so, and have good stratification.

 

[hartkem]

Thanks for all the opinions. The coil piping just seemed more simple but my storage tank may not have flow as maple mentioned. The temp should be ok. I need to do some more research regarding the flate plate.