Oil Fired combi boiler?

Actually what you have is pretty good — a quality modern oil boiler firing a hydronic system. The downside is keeping the boiler warm for the domestic hot water. You might gain some efficiency by using an indirect hot water heater, such as a SuperStor, heated by the boiler but storing a good deal of hot water, like a regular hot water heater. It works like a separate zone off the existing hot water heat.

What you will NOT find is an oil fired "combi" in the modern usage of the word — which also implies "mod/con" — that is modulating. Those do have slightly higher rated efficiencies, true — but they are only for LP or natural gas, as modulating an oil burner is really remarkably hard and there isn't that much to be gained anyway (oil is naturally more efficient that either LP or gas under otherwise identical conditions).

@TdiGuy

Yes EK is the way to go, or you’re going to have to go to Europe or Asia for one.

I have a Bock tank which I use for hot water and hydro-air. I think that a switch will not save you any significant amount of oil. Perhaps changing equipment is not the best cost saving approach. Are you using a "full service" oil dealer? You could be paying for high cost services you are not using. I use a pay as you go dealer and rely on my plumber for service. There are also independent heating service companies. Pay as you go dealers are usually have a much better oil price. Also, consider if you need annual service calls. I only have my equipment serviced every other year because of low operating hours. I heat with wood

Hay @TdiGuy, An oil-fired boiler with a tankless coil is about as close as you are going to get to a combi system with oil heat. However, I would not recommend that approach.

Where are you located? What is the price of Fuel Oil v. Electric in your area? And finally: Do you use wood heat to reduce your fuel oil usage? Answering those three questions will send you to or away from some suggestions above.

Gas-fired mod-con combi boilers are a step above that because they do not maintain a minimum water temperature the way an oil-fired boiler with a tankless coil does. That is why I say they are a step above. Even so, I still would not recommend a combi system, for at least two reasons.

The expected life of a tankless water heater is generally less than 17 years, even if all the required maintenance is completed properly during that time. With a combi system, both the heat and the domestic hot water come from the same device, even though those two functions have different demands and different potential problems.

Either the heating side or the domestic hot water side could become the determining factor in replacing the entire heat and hot water system. An expensive failure any time after the fifth year could mean buying a complete new system. That could happen because of a failed control board related to the heating system, a domestic hot water problem caused by improper heat exchanger maintenance, or any number of other issues that can occur.

That said, an oil-fired boiler that maintains a minimum temperature for domestic hot water all summer long is, in my opinion, a waste of energy. In most cases, that boiler is connected to a chimney. The chimney continues to draft, pulling heat out of the boiler’s heat exchanger while cooler basement air is drawn in to replace the warmer air going up the chimney. That standby loss can cause the burner to operate every four to six hours just to recover the heat lost up the chimney, even if you dont open a hit water tap during that time.

If you were going to install a gas-fired mod-con boiler, I would choose a heat-only model and connect it to an indirect water heater. That would give you the energy-saving benefits of outdoor reset control and the small water content associated with mod-con boilers.

Since you are suggesting that you want to stay with oil heat, I would choose the most efficient cold-start, heat-only oil boiler available in your area and connect it to an indirect tank for domestic hot water. That will get you as close as possible to the most energy-efficient oil-fired system you can have.

The burner is large enough to heat your home, so it has more recovery capacity than an oil-fired stand-alone water heater. The indirect tank is not connected to a chimney or any other vent system, so the standby loss is measured over a much longer period, often 12 hours or more, and as much as 20 hours on some well-insulated models.

That means if you go away for the weekend and forget to set the water heater to a lower temperature or vacation mode, the burner may only operate once for less than ten minutes every 12 to 20 hours to make hot water. That is very different from a tank of hot water connected to a vent system that can constantly pull heat up the chimney.

The main heating boiler can operate as a cold-start boiler, and the boiler temperature can drop as low as the basement temperature during that standby period. That will vent far less energy up the chimney than keeping a boiler hot all summer just to maintain a tankless coil.

Indirect water heaters also tend to last longer than tanks that have flames directly under them. Some even have lifetime warranties. It might be the last water heater you ever purchase.

Energy Kinetics has one of the best offerings, as you may have seen in a previous post. I would look closely at that one. Your fuel dealer may wonder if you started buying fuel from someone else!