Monday, March 9, 2009

Tanks But No Tanks

High Efficiency Water Heating Compared

Having hot water at the simple turn of a tap is a great convenience. How your water is heated makes a difference. An efficient water heating system saves you money and reduces pollution. Water heating is about 15 percent of an average home’s energy use. An efficient system can cut that energy usage in half or better.


Our home came with a conventional natural gas, tank water heater. It recently went on the fritz. This is our opportunity to upgrade it. So what type of water heater to use? 

Of course given the name of this blog, the first consideration was solar hot water heating. More on that later. First, let's look at the options. Below is a chart of efficient water heaters from energyStar.gov.

High Efficiency Tank: These are conventional water heaters with highly insulated tanks. These are great for retrofits and not much more expensive than a traditional tank, but not that big of an energy savings compared to the other options. The drawback to this type is the energy used to keep the water hot at all times, known as “standby losses.”

On-Demand aka Tankless: These have been popular in Europe for years and are only now starting to have a significant presence in the US market. These heat the water when it is needed and so avoid the standby losses. There is no tank. Heat it when you need it; that is eloquent. And you have the benefit of "never running out" of hot water. Gas models do require a larger gas line than a tank water heater, so retrofitting may be difficult. You can buy these at various flow rates. Be sure you get a unit that can keep up with your household's needs.

Heat Pump aka Hybrid: These are relatively new to the market. Heat is extracted from ambient air and transferred into the water. When the air is too cold, then the "hybrid" models switch over to electric water heating mode. GE has a model planned for 2010, but I was unable to find any major brands that produce these today. If you must heat with electricity, this is your most efficient option. 

Solar Water Heating: This type costs the most up front, but they often don't need fuel and can "pay you back". The Sun’s energy is harnessed to reduce operating costs up to 90 percent. Since the Sun is not always out, solar water heating systems require a secondary water heater as a backup. Solar water heaters have their own tank. They either send the water itself up to be heated or another medium can be used and then the heat is transferred from this medium to the water. The advantage of a medium is that it can be something that does not freeze in the winter. Whereas water based systems must have a drain mechanism to make sure no water is left where it can freeze and burst a pipe.

So now we know something about each type. The first place I called was my solar installer, they install hot water systems too. They came out and looked at our setup. As it says above, solar hot water heating requires a tank of its own. So I would replace the tank system that we have now with a high efficiency tank and then add solar as a preheating system. This doesn't work for our little garage since we don't have room for two tanks. There is also an option for a single tank, this is electric when the solar cannot get the water to temp. The problem with this one is that our water heater is jammed in-between our furnace and a staircase. This single tank system was too big for the 23-inch space that we have. Unfortunately, it looks like solar water heating will not (yet) work in this house. 

The next most efficient system on the list is tankless. We had two contractors come out and give us quotes for a tankless system. The prices were outrageously different. The first one was in-line with what I expected. The second one was twice as much, wow. 

I checked out the CCB # of the cheaper quote and the brand of tankless that he recommended. It all looked good, so we are going tankless.

The tankless unit is going to be placed on the inside of the exterior wall so the new gas line can easily be run to it. This is what both contractors recommended. It means, however, that the water lines are going to be run across the ceiling of the garage. Too bad our house was not just built for tankless in the first place. 

The good news about the tankless unit being placed on another wall is that now we will have room for a solar tank if we want to add solar in the future. However, now that our water heating bill should be down to about $8 per month, I think other green projects will be higher on the priority list. Like adding more panels to the PV system.

We are taking this opportunity to install a whole-house water filter too. We had our water tested at a local lab to see that type of filter to get. Our water checked out great so we are getting a simple chlorine filter. 

When the system is installed, I'll post before and after pictures and discuss the High Efficiency Water Heating Incentives that I found. 

Links:
Energy Star Hot Water Guide

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