Craftsmen of Homes

540-797-3059

Roanoke & Smith Mountain Lake, Virginia

Tankless Water Heaters

We are often asked about these types of hot water heaters.Rinnai tankless hot water heater for new home design and built at Smith Mountain Lake by house builder Timber Ridge Craftsmen Inc. Bedford County, Franklin County, Roanoke County, Blue Ridge Mountains of Virginia.

Tankless water heaters, as the name suggests, have no storage tank where heated water is stored till use.  Hence there are no stand-by heat losses from a tank.  These can respond instantly to demand, running hours continuously if need be, and so are also called 'instantaneous' hot water heaters.  Although there are both gas and electric versions of these, you will find far more gas units than electric - and for good reason.  If you saw the older-style electric meters that have the spinning meter wheel, and observed the current draw of the electric tankless units, you'd wonder how the wheel doesn't fly off its pivot and spin into earth-orbit.  Dramatic, to say the least.  Gas units are the 'go to' version of tankless water heaters, and electric should only be used for infrequent or minor applications.

The instantaneous tankless hot water heater pictured at right is a Rinnai model, fueled by bottled liquid propane gas supply at a new home designed and built here in Bedford County at Smith Mountain Lake, Virginia.

You may have heard about the desirability of tankless hot water heaters from a friend, a plumber, or a builder.  You may have heard they can save energy cost, and qualify for either credits or points from various utility or green building programs.  Rather than rely on someone's word or a program recommendation, we do prefer that your home design and build solutions are tailored to your particular goals, and that energy-modelling tools are used to provide you with some objective inputs into the decision process. Energy modelling is in no way perfect or even precise. But such modelling is better than 'a guy told me I just had to use this'.

Electric resistance water heater energy modelling for new home design and built at Smith Mountain Lake by house builder Timber Ridge Craftsmen Inc. Bedford County, Franklin County, Roanoke County, Blue Ridge Mountains of Virginia.

Using the above graph as a standard baseline for study comparisons, notice that this new airtight, well-insulated energy-efficient home has a typical electric-resistance tank hot water heater installed.  Hot water heating costs are projected to exceed the space heating costs (that's heating the whole house with an air-source heat pump, annually).  This is a rather common finding in high-performance homes.

Let's next compare the above pie chart to the same home, modelled with a new liquid propane (LP) tankless hot water heater.

Tankless LP gas hot water heater energy modelling Smith Mountain Lake, Timber Ridge Craftsmen Inc. New home design and house builder. Bedford County, Franklin County, Roanoke County, Blue Ridge Mountains of Virginia.

The above graph is based on a typical residential instanteous tankless hot water heater with an energy factor of .93 and liquid propane (LP) delivered cost of $1.60 per gallon, which is the current summer-time price from a reputable propane firm here at Smith Mountain Lake.  Comparing the water heating cost of $150. here to $414. in the top graph, you can see a predicted annual savings of $264.  Will the actual savings be precisely that ?  Of course not; the savings will be subject to a host of factors, some knowable at the time of energy modelling, some not.  But the general trend here is helpful in making wise purchase and planning decisions.   With predicted annual savings of $264., we anticipate an eight or nine year simple payback on this decision, compared with the basic electric-resistance tank hot water heater.  Was that better, or worse, than you thought ?  

Lastly, let's look at the same home, same type of pie chart, which shows a similar instanteous tankless gas hot water heater - fueled by "street gas", which would be natural gas.

Tankless natural gas hot water heating energy modelling for new home on Smith Mountain Lake by Timber Ridge Craftsmen Inc. Home design and house building. Bedford County, Franklin County, Roanoke County, Blue Ridge Mountains of Virginia.

The savings is similar to - if a bit better than - the liquid propane (LP) gas modelling results.  The benefits of street-gas infrastructure are real, even if relatively few residential areas here in the Blue Ridge mountains of Virginia are served by natural gas supply.

Pros & Cons of Tankless Gas Hot Water Heaters

Clearly these types of hot water heaters can provide a simple economic payback, and are worthy of consideration.  Additionally, they are 'instantaneously' responsive to demand - which means that they are well-suited to homes that have substantial variability in how/ when hot water is drawn. For example, here at Smith Mountain Lake (SML), many homes are occupied year-round by a couple, which is likely a light annual demand on any hot water heater. However, since SML is such a desirable vacation spot, adult chidren/ friends/ family join parents here in the warmer months for frequent visits and vacations.  As such, the demand draw can be much higher during a busy week/ weekend - where many family members want to take showers about the same (1 to 2 hour) time. Tankless hot water heaters can be configured to keep up with most of that demand variability in a reliable and satisfying manner.

Factors which should be considered before choosing this kind of water heater include:  recommended number of tankless units necessary to keep up with maximum demand, simple installed costs, variability in liquid propane (LP) fuel costs, and water quality issues.  Regarding the number of tankless units necessary, would it surprise you to learn that there is a maximum Btu output for each tankless model you consider buying.  Once an analysis of the maximum water-fixture demand in the house is done, and a discussion is had regarding how many visitors/ how many simultaneous showers, it is common for folks to seriously- consider installing two such units to work in tandem (think large occupied house during a holiday weekend).  

Installed costs are an issue:  these are not inexpensive to purchase or install, especially when better equipment and higher-Btu outputs are desired.  Variability in LP fuel costs are a given, but fortunately in most years are subject to seasonal demand patterns.  The smart strategy here is to install a large underground LP tank at time of site planning/ building, and then purchase a year's worth of fuel during the summer when prices are lowest.  Water quality can be also be an issue.  In our area of Bedford and Franklin counties at Smith Mountain Lake, most water is drawn from private water wells drilled on site.  Given the typical subterranean rock strata here, it is common for water treatment of some type to be necessary.  While water treatment may seem optional to some, and water hardness (for example) viewed more as nuisance than hazard, if you invest in a tankless hot water heater then you don't want calcification/ mineral build-up to damage the heat exchanger.

Solar Electric PV & Tankless Hot Water Heaters

In designing and planning low-energy and net-zero energy homes here in Bedford and Franklin counties near Smith Mountain Lake, we often recommend diversified fuel-energy solutions.  The prime reason for this is redundancy and resiliency in future-proofing a homestead.  The volatility of weather events, and commodity-market fluctuations, are predictable enough - in looking years into the future. 

The need for site solar electric (PV) solutions is a given, and with falling install prices every home site should be future-proofed for it.  If hot water heating is fueled by gas, and not electricity, it is easier/ quicker to take a home to net-zero (site) and even off-grid because fewer PV panels and less storage is needed to do so.


Timber Ridge Craftsmen, Inc.                                                                             540.797.3059

One of Virginia's finest custom home builders, with extensive experience building with SIPs, ICFs, Timber Frame, Hybrid Timber Frame, Log, Panel, and Modular construction systems. Smith Mountain Lake, Roanoke, Bedford, and Franklin Counties, in the beautiful Blue Ridge Mountains of Virginia.      Google +      Houzz

 

 

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