Hello, I am a homeowner in NC mountains where we get cold winters. We are currently paying around $3000 per year for propane plus another 1500 per year for electricity. We are researching options on ways to reduce our energy expenses. We have a 60 gallon hot water heater and an propane HVAC system. We also supplement our heat with a woodstove throughout the winter.

My thought is I would like to switch out our water heater and replace it with a solar hot water heater. We have not done so yet because my husband and I keep disagreeing about which direction to go. He wants to switch out the entire heat system...actually he wants to add solar radiant heat but hook up the HVAC system as the default. He also thinks that we can run a tankless hot water heater through that system. He keeps telling me how affordable it will be but I am doubtful. I would rather go the direction of just keeping HVAC heat and replace solar hot water heater and maybe add wind turbine. Especially because in NC we use 50% coal to power electricity.

Thoughts? thanks...

Posted By dharmama on 31 May 2010 07:38 AM
Hello, I am a homeowner in NC mountains where we get cold winters. We are currently paying around $3000 per year for propane plus another 1500 per year for electricity. We are researching options on ways to reduce our energy expenses. We have a 60 gallon hot water heater and an propane HVAC system. We also supplement our heat with a woodstove throughout the winter.

My thought is I would like to switch out our water heater and replace it with a solar hot water heater. We have not done so yet because my husband and I keep disagreeing about which direction to go. He wants to switch out the entire heat system...actually he wants to add solar radiant heat but hook up the HVAC system as the default. He also thinks that we can run a tankless hot water heater through that system. He keeps telling me how affordable it will be but I am doubtful. I would rather go the direction of just keeping HVAC heat and replace solar hot water heater and maybe add wind turbine. Especially because in NC we use 50% coal to power electricity.

Thoughts? thanks...

Air sealing & insulating the place to the extent possible would come WAY ahead of any solar solution.  If your clear-wall R values are under R30, and your air leakage is over 1 ACH @ 50pascals pressure  the size & expense of an active solar system to support your heat load would be ridiculous.

Assuming your HVAC isn't too oversized and isn't a "high efficiency" unit it probably has a real-world AFUE of ~75-80%, and  uses conditioned-space air for combustion.  If the HW heater is a propane-fired heater with a standing-pilot ignition & is atmospheric drafted, it's probably running ~ 50-55% efficiency.  If it's electric, it's running ~85-90% efficiency.  An in-floor radiant system running on the propane will run better than 90% if a modulating condensing boiler (or condensing tankless HW heater) is used.  The same boiler could be used to heat hot water in a separate "indirect" tank, or a solar HW tank as well (but at only ~88-90% efficiency due the the higher temperature requirements for DHW.)

Do you have a full basement or crawlspace?  Are it's exterior walls sealed & insulated?  (If not, they SHOULD be- it could easily be 20% of your total seasonal heat loss.)

If a full basement, and you take shower rather than baths you can get far quicker payback than with solar with a drainwater heat exchanger on the main drain to the house feeding back heat to the cold supply to the shower & HW heater.  (It takes a section of vertical drain at least a 4" diameter 48" or taller, or a 3" drain 60" or taller to fit a decent one.) No matter how you're heating hot water, the value is there- it enhances the solar-fraction of solar HW, reduces fuel/electricity use of other systems.

Are you in an area that offers off-peak rates for electricity?  Using off-peak electricity for heat (and hot-water pre-heat) is often substantially cheaper than propane.  Since your peak heat loads typically occur during off-peak hours (typically between 10PM & 6AM), buffering off-peak energy in a tank or concrete slab for day-time power use can often result in HUGE savings.  (And if your local grid is running on nukes & old-school coal it means you're using energy that would have otherwise been wasted in power-dumping systems to avoid the inefficiencies of having to shut down & restart the generator.)

Have you replaced all of your lighting with high-efficiency linear fluorescents/compact-fluorescents & or better quality LEDs (only the best of which beats compact fluorescent efficiencies, but not yet clobbering electronic-ballasted T8 or T5 long-tube fluorescents)??  Are you switchin any of the lighting off occupancy detectors to make sure they turn off when unneeded/unattended?

Is your clothes washer a better-efficiency front loader, using a fraction of the water/hot-water of a top loader, and able to clean clothes with warm or even cold water better than a top loader does with warm/hot?

A lot of stuff comes way ahead of replacing heating/hot-water systems.  To be effective, you have to be COST effective.

Dana, as always, has done a fine job of discussing the possible problems and solutions for you.
Let me add a couple thoughts.
The most likely problem area will be:
Air infiltration. Caulk and seal around doors, windows, seal plates, electrical outlets, etc. Any place air can get in.
Caulk and spray foam are cheap and easy installs. You may need to remove window/door casings to do a thorough job.
Attic insulation: I don't know the age of your home, however, if you have not upgraded the attic insulation, it probably needs to be upgraded.
HVAC duct leakage: This is a common problem with systems more than a few years old, at least in my neighborhood. Lack of attention to detail by installers, and lower quality materials can lead to more air in your crawlspace/attic than in your house.
Lastly, have your HVAC unit thoroughly inspected, and adjusted. If your unit is a 'gas-pack' with all the equipment in the outside unit, is more than a few years old, and the upkeep has been less than perfect, its efficiency may be severly hampered.

Excellent point on the duct leakage issue. Duct location & design counts too. If it's imbalanced you may need to build in jump-ducts & return grilles between rooms to keep it from generating infiltration-inducing pressure differentials. If the ducts too small, sometimes sealing them will create frost up issues with the AC (not enough air flow if they're not leaking!), but you can cross that bridge when you come to it. If they're located in unconditioned space, insulating them (both supplies & returns) can be huge.

Solar & wind are great, but if it's about lowering your carbon footprint, enhancing the efficiency of the building envelope & existing systems usually buys far more carbon per dollar invested, and is the highest first-priority. Only after those measures are taken will the size of the renewable-technology required become anything like affordable. A lot can be done with deep-retrofit before solar or wind becomes the next-most-cost-effective thing to do, eg:

https://www.powerofaction.com/media/pdf/DER_CaseStudy.pdf

Low temp active or passive thermal-air panels are far less expensive/ more effective retrofits than active-hydronic systems for space heating or hot water, but even there you can often buy a lot more insulation, foam, & caulk for the money, if there are still places that need it.

Solar hot water for a two-person household is typically $6000+ to install and would only save ~150-175gallons of propane or ~3500kwh/year. Drainwater heat recovery is more like ~$1-1.5K and saves about 60gallons or 1500kwh/year at NC water temps (more, in colder regions.) But applying the same $1-1.5K to air-sealing & insulation or building-in thermal-air panels will save much more. You really need the bigger picture on what's going on in the place (and the budget constraints) to properly prioritize the retrofits. But most people haven't even sprung $20 to insulate the near-tank plumbing on the HW heater (with sub-1-year payback!) let alone fully insulated all of the accessible hot water distribution plumbing with 3/4" -wall closed cell foam pipe insulation (a cost effective upgrade from the 3/8" wall stuff found at big box stores, but you may have to buy it online, plumbing supply houses, or Graingers, etc.) Typically 15-20% of the hot water heating energy is abandoned in distribution plumbing, and 85-90% of the energy that went into a shower goes literally down the drain. Buying hot-water sipping EnergyStar washer & dishwashers, insulation the plumbing, and installing drainwater heat recovery typically cuts hot water energy use roughly in half for less money than the solar HW system needed to supply that half.

If your husband is great at DIY and is still sold on solar radiant, keeping the existing HVAC in place for cloudy days, and hacking a low-temp atmospheric drainback system is possible (but I wouldn't advise using a propane-fired tankless as back-up on it for many technical reasons.) For a primer on how it's done see this existence-proof:

http://www.builditsolar.com/Projects/SpaceHeating/SolarShed/solarshed.htm (DO pay attention to details- they count! The designer in this instance is an aerospace engineer.)

So many intriguing and free thinking sites to read and possibly implement on the net, thanks Dana!

John