Tankless with a super-stor

[masstech]

I'm currently quoting a boiler for a community development block grant and the spec calls for a boiler with a tankless coil and a 30 gal. super-stor on the side. Is there a real cost savings or advantage to the home owner by doing this or are they better off going with just the tankless coil or just the super-stor and save money on the installation cost?

[johnsp]

The issue I have with a tankless coil is the flow restriction and you cannot cold start the boiler. I would invest in a circulator rather then the coil and just heat the indirect off the boiler on demand. Also put the indirect on priority if there's no excess BTU's in the boiler.

[splus]

Did a few tankless like these and there working out great.What is the application you are looking at.how are you venting the equipment if sidewall a tankless will cost less

[nutshell]

Stay away from the tankless, flow restriction among other issues you will run into. Superstore with a Sparco mixing valve should provide all the hot water you will need providing it is sized right.

[Noel Murdough]

Go with the cold start boiler and the indirect. The mixing valve (if the correct one) is also an excellent idea.

Noel

[masstech]

Thanks for your imput. My initial feeling was to go with the indirect.

[casturbo]

I won't disagree the indirect hwh is the best source of hot water. But running a system with a cold start control kills boilers. EVERY cold start OIL boiler I service (no exaggeration either) is loaded with scale and has efficiencies way below 60%. Name brand cast iron boilers are the most sensitive too. A consistently warm boiler is a clean boiler. Oil consumption on a boiler that maintains a low limit temp is maybe 15 gallons a month in the summer....running a dirty cold start boiler costs ALOT more than 15 gallons a month. Something to think about.

My source of hot water in my home is technically called an aquabank. Meaning, I have a storage tank that stores hot water made by the tankless coil in my boiler. My low limit is set for 130°F. It works very well. Restriction thru a hot water coil is minimal and actually, there is alot more restrictions elsewhere in a house (shower head for example) that is more of a concern. My storage tank, by the way, is a discarded electric hot water tank. The 220 volt electric elements are disconnected and the thermostats in the tank now run a recirc pump when the tank cools off during the day. Works incredibly well and is soooo cheap to install.

[Al Gregory]

You sure they arent talking about a tankless coil and a Super Store Aqua Booster. A tank that uses a bronze circ to circulate water through the tankless and store it in the tank.
There is no coil in the tank. Its basically just used for storage.

[johnsp]

I disagree. Having a coil that can lime/scale up. The gasket starts leaking after 10 years, and you have to heat up the space durring the summer keeping the boiler at temp. Plus you have an expensive bronze circ that might need replacing some day. Just get a low mass steel boiler like the Burnham LE. Why keep 10 gals + of hot boiler water in the boiler so the BTU's just go up the stack? Low mass is used in just about all the condensing gas boilers. Why should an oil boiler be different.

[casturbo]

Originally posted by johnsp
I disagree. Having a coil that can lime/scale up.

True, but recovery with an aquabank style hot water heater is not important. So even if the coil limes up, it will continue to be effective for quite some time. I see it firsthand in my location....tankless coils without storage tanks have a hard time supplying alot of hot water, but the same setup but with a storage tank at the very next house (figuratively speaking) is just fine. Hot water is all about how much you can store, not how fast you can make it. Take for example the typical indirect hot water makers (Phase III, Bock, BoilerMate, etc), their hot water making ability is maybe 3 gallons per minute. That is not alot of hot water recovery.

Originally posted by johnsp
The gasket starts leaking after 10 years,

After 10 yrs?...kinda an exageration. But if it does leak, the gasket is cheap and the repair is not all that tough on a cast iron boiler.

Originally posted by johnsp
and you have to heat up the space durring the summer keeping the boiler at temp.

A warm boiler is a clean boiler. See my original comments on cold start boilers.

Originally posted by johnsp
Just get a low mass steel boiler like the Burnham LE. Why keep 10 gals + of hot boiler water in the boiler so the BTU's just go up the stack? Low mass is used in just about all the condensing gas boilers. Why should an oil boiler be different.

HUGE difference in my experience comparing gas with oil boilers. The Burnham LE in my experience, as well, is not a great boiler (at least with a Beckett AF burner). Never seen one run clean yet. Cold start wreaks havoc on all oil boilers, even more dramatic on the low mass units. They can't take any clogging of their flue passages whatsoever, so they soot up real fast.

[johnsp]

True, keeping a boiler warm 365 days a year is best for the boiler. (But not my wallet at over $2/gal I like using the reverse indirects like ErgoMax, Dunkirk Artesian, etc. since they hold 20 gals of hot boiler water. When the aquastat calls for heat and the boiler fires, the indirect circ is sending 120° water to the boiler, not room temp water from the baseboards and rads. I guess what I'm saying is that I like the tankless coil, I just think it should be placed in an insulated tank rather then in a boiler that will easily loose BTU's up a flue pipe. My fear of snapping a rusted bolt on a coil gasket swap could turn a simple fix into a painfully long repair.

[oilman]

I like both ideas. I like coils with boosters, however, I also like the Ergo Max- Artesians style of heater.However, I would still have a low limit. The thing that casturbo said that was missed is that your low limit w/ an aquabank can be lower than coil only.

[casturbo]

Originally posted by oilman
....The thing that casturbo said that was missed is that your low limit w/ an aquabank can be lower than coil only.

Yes, I fully agree. I run my boiler's low limit at 130°F and even at that low low setting, the tankless coil makes hot water easily.

Standby loss is .50 gallon of oil per day, so roughly $1 per day to keep the boiler running at top efficiency. If the boiler was coldstart, I'm sure standby loss would be less, but the boiler in a few months time would be scaled up and efficiency would be poor....negating all savings of coldstart and adding oil consumption beyond what it would take to keep the boiler at a low limit setting.