Best Of
Re: Indirect HW off steam- shaking circulator
You will not get very much heat into the indirect, if you're only flow is through the bypass loop. And just for the record, I have piped many indirect off of steam boilers, without any bypass loop.
Re: Indirect HW off steam- shaking circulator
I see no need for a flow check. All the flow check does is add a restriction. Its purpose is to prevent gravity flow. The amount of gravity flow from the top of the boiler to the bottom of the boiler is negligible.
As far as the flow through the indirect it should be as the tank mfg recommends. However reversed flow may not change the operation of the tank that much.
I would assume they would put the hotter boiler water into the lower coil tapping as you will have colder DHW at the bottom of the tank don't know if this is true.
Re: Indirect HW off steam- shaking circulator
@WilliamME … I have been following this for a while and see that you have asked if several different things can work outside of repiping the system correctly.
My first thought after looking at your pictures is to open the FlowCheck valve to the manual open position and flip the circulator pump to pump from the bottom of the boiler to the water heater return tapping. Just turn the circulator around. That is easy with the valves there. You could do that yourself. This will be positive proof in your mind that pumping away from the lowest point in the boiler WILL solve your problem.
If you find that the water heater overheats when the circulator pump is off, then you need to install the flow valve properly. That will involve some repiping. At that point you should have it done correctly.
Re: Which Viessmann boiler to buy?
You could also just replace the current oil burner with a gas power burner. 20 years is still pretty young for a boiler. It could leak tomorrow or it could last another 30-40 years. Without some heat loss calculations you don't know if your current boiler could pick up your loads or not. If the conversion to gas is propane it likely isn't going to be cost competitive to oil. The 125 gallon tank probably can't handle the drawdown of a boiler in winter so the new propane tank would be a significant expense. The cost of replacing the boiler is going to far exceed any fuel savings once you account for the piping and trim and labor.
mattmia2
Re: Which Viessmann boiler to buy?
I would say the Vitorond or the CU3A would be good choices. Both boilers are very good. The issue I've had were the CU3A would have been a great choice for a replacement boiler was ceiling height in a"Michigan" basement. Basically a glorified crawl space. I just didn't have the headroom for the boiler. The CU3A is easy to connect to a majority of piping arraignments with little modification. The CU3A is going to give you a few added features with the controls like OAT reset.
The Vitorond casting is well built, but heavy to move . We had a customer purchase one and put a waste oil burner assembly on it for his shop. I attached a pic so you can see what the casting looks like. A plus on the Vitorond would be that you can change over the burner to gas at a later date if you decide fuel oil is no longer the route you wish to go.
The question is what fuel you would like to go with now propane vs fuel oil. Factoring in the fuel oil tank replacement vs a 1000 gallon propane tank installation is sort of a wash. I would treat this as a separate bid then compare just the boiler installs. We don't discuss actual prices here. As for the Carrier acquisition of Viessman, I have not yet seen any changes in service from our Viessman rep or supply houses. It's still my go to mod con boiler choice.
Re: Which Viessmann boiler to buy?
The 600gallon/year oil use puts your heat load around 30000BTU, you are oversizing by a fair bit with the Vitocrossal 300 CU3A. I would run through the math here to get your heat loss nailed down and go from there on selecting a new heat source.
Oil heat has completely disappeared around me due to operating and maintaince costs.
Kaos
Re: Indirect HW off steam- shaking circulator
Turn the pump and flow check valve around and pump in the other direction.
The resistance of the flow check and the resistance of the indirect coil are starving the pump and causing cavitation.
Can't say if turning thoes two items will be a 100% fix. The suction pipe coming out of the boiler should be 1" minimum and it would be better if it was larger. All indirects should have minimum 1" pipe.
Turning those two things may get you by
The flanges on the circulator can be changed to accommodate this. Keep the circulator as close to the floor as possible.
Your installer screwed up
You always locate a circulator to push against high restriction not pull through high restriction.
Re: Indirect HW off steam- shaking circulator
This type cavitation is about dropping below the vapor pressure of the fluid. So temperature and pressure are involved. More on this below.
hot_rod
Re: Indirect HW off steam- shaking circulator
Your situation, like so many, is complicated. Thanks for the additional info.
It sounds like maybe you haven't paid them in full yet? That is good. Surely I wouldn't pay someone for an install that wasn't working.
I don't think that just reversing the pump direction is going to solve everything. Boiling hot water will still enter the pump, and that is going to cause difficulties I think.
Just for fun, here is a link to my hot-water loop that I slapped together. It is not going to solve your problems, but it might give you some ideas about how you could put in your own bypass and it might make the ideas clearer in your mind. Good luck! (bypass loop talk starts at 8:30 into the video)
Re: Indirect HW off steam- shaking circulator
Taking pumped suction from a steam boiler isn't complicated at all. But it is also not forgiving at all, and there is only one way to do it right.
The pipe from the boiler to the pump must be the same nominal size as the tapping on the boiler or the inlet diameter of the pump, which ever is larger. It must be absolutely straight for a minimum of 12 pipe diameters before the pump inlet and should not be longer than 12 pipe diameters, or if the pump can be set lower than the tapping that is permissible, but the lead to the pump must still be that diameter and straight for at least that length, and the pipe size should twice the diameter otherwise required. . If there is a valve on it, it must be a full port ball valve. The tapping on the boiler which is used must be the lowest available tapping.
Then, and only then, do you have a reasonable chance of not having at least occasional cavitation in the pump and early pump failure.
