For a while now I’ve been planning to get a Triangle Tube Smart Series indirect water heater. Indirect water heaters use the boiler to heat the water rather than have built-in heating elements. Lester, our radiant heating guy, agreed that it was a good design but cautioned that there can be issues with getting them approved by inspectors because they don’t have a double walled heat exchanger. I looked into the code and determined that we shouldn’t have an issue with that, but for a number of other reasons I wound up looking at other water heaters anyway.

The first is simplification. Our project is really complicated, with a set of interlocking pieces with dependencies and requirements across the gamut. Our existing water heater is in the way of our new boiler panel installation, so if we use an indirect water heater, we need to first move our existing water heater (disconnect everything, move it, and run water and gas plumbing to the new location along with exhaust flue to the chimney). Then we’d get the new boiler installed along with the indirect water heater, and re-plumb the water lines to the new location. We wouldn’t be able to remove the chimney until the new system was fully up and running. Conversely, if we just buy a standalone water heater, we can install it soup-to-nuts and be done with it. The boiler install loses any other dependencies, the chimney isn’t waiting on anything else, and we don’t have a single point of failure (the boiler) down the road.

There’s a few other factors to consider. For one thing, when the home is tightly insulated our heating load will be quite low. Having an indirect water heater actually means we’d need to buy a bigger boiler. The boilers modulate, meaning they can run at different levels depending on load (25%-100%), but if the boiler needs to be bigger just to run the water heater, that 25% is still a much bigger value. Our plumber, Mariusz, recommended the AO Smith Vertex 100, and it’s easy to see why. It’s 96% efficient, it’s reliable, we’ll never run out of hot water, and it’s direct vent, so it uses outside air for combustion, which is important when we’re doing so much air sealing.

I’ve already decided against tankless. They draw too much gas (up to 199,000 btu) and they don’t work well in the Midwest where our cold water can be 50° F or less. I’ve decided against tankless hybrids since they seem unreliable. I’ve ruled out most of the other condensing storage models because they either cost more, produce less, are less reliable or some combination thereof. There are cheaper models that direct vent but in addition to not having as much capacity (first hour delivery not tank size), they’re more than 40% less efficient, easily costing more over their lifetime.

Vertex 100

Vertex 100

In the end, I did a cost comparison. The Smart Indirect is the cheapest until you factor in the cost of a bigger boiler. A lower efficiency direct vent water heater is cheap until you factor in the operating cost. The Vertex 100 is expensive, but its high efficiency will pay for itself. I also looked at a more expensive direct vent heater that had a stainless steel tank so it would last longer, but the payback wasn’t there. I’ve reached out to Mariusz to get the ball rolling. In the mean time our whole-house water filter showed up and I need to frame out the mechanical room wall.

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