Optimization of heating efficiency first requires determining your specific requirements. In general terms there are two or more distinct heating energy uses:
- Area Heating – Warming occupied areas fully, or selectively as living habits occupation or use may demand.
- Domestic Hot Water (DHW) – Heated, potable (drinkable?) for baths, showers, laundry and personal consumption.
- Special Uses – High temperature power washing, sanitizing, etc. (Refer to prior blog.)
All of these requirements can ideally be met by using a hot water boiler system as a single, central source but the question arises of how to accomplish this efficiently. Specifically, varied heating demands that may range from continuous (?) DHW to very occasional (seasonal?) and selectable area warmth can become a challenge, particularly economically. These occasional demands can “lighten your wallet” to execute and maintain. Let’s address this problem systematically.
Arguably the most important decision has to be your heating fuel selection. We cannot overemphasize this and the use of a Heating Cost Comparator to define your choice. (See our other blogs.) The standard unit of measure is the “Cost per Million BTU” expressed as a dollar figure. We use the NH-OEP Calculator at http://www.nhclimateaudit.org/calculators.php for our area usage, but similar ones are available in your locales. Use your current or projected new heating appliance efficiencies (AFUE) to get an accurate calculation. New Gas (Natural or LP) AFUE’s are typically 95% for top end (condensing) boilers and 87% for Oil Triple-pass boilers.
The current and foreseeable heating fuel choices have become quite obvious in the northern climates:
- Natural Gas (where available) is a bargain and promises to continue to be so. But BE CAREFUL! Natural Gas is a “distributed fuel” (through a pipeline). Your actual bill will be considerably higher due to service and distribution costs added to your actual therm usage. Get a billing estimate from your gas provider first! (Our local multiplier is about 1.3 or 30% adder for actual natural gas billing costs.)
- Heating Oil is the predominant fuel where natural gas is not available.
- Liquid Propane (LP) Gas is another option along with oil where natural gas is not available. LP has predominantly been used for domestic cooking and somewhat for DHW generation. As an area heating and DHW fuel it has traditionally been up to a 65% premium over oil. Even with the recent spike in oil prices LP is still a 28% premium locally.
Note that solid fuels (wool, coal, peat, waste, etc.) have been purposefully omitted from this discussion. Insurers typically disallow continuous firing fuels using interior combustion equipment. Their use externally typically requires interfacing with an internal power fired system to assure continuous heating maintenance. Verify these statements and weigh potential penalties for your particular situation.
Consumers predominantly identify their area heating options as Forced Hot Air (FHA) Furnace or Forced Hot Water (FHW) Boiler Systems. Similarly DHW options as Electric, Gas or Oil stand-alone Water Heaters or from an immersion coil within a boiler. So therefore we usually find the typical FHA System with a stand-alone DHW Heater as a combination. FHW Systems usually provde DHW from an internal Immersion Coil, as previously noted. (More recently we are seeing the emergence of the Indirect Hot Water Heater, supplied by a boiler as the efficiency choice.)
But in fact our heating options are more extensive. They include:
- Air Handler – A FHA Furnace without a fuel-powered heating source. Instead it has an internal large radiator (heat exchanger) that is supplied with energy from an external FHW source (boiler).
- Unit Heater – A radiator with fan, typically found as an overhead heater in a garage, warehouse, etc. There are also variations of these with provisions for attaching ducting – otherwise similar to an Air Handler.
- Plate Heat Exchanger – Basically two (or more) mutually integrated radiators allowing the interchange of heat from varied sources. Source variation attributes may be pressure, temperature, flow rate(s) and composition. Their composition may be aqueous (or not) and adjusted for properties such as freezing and/or boiling resistance.
Utilizing these latter devices allows us to employ higher efficiency or lower cost hot water generation sources (or both) for all our area and DHW heating requirements. We respectfully suggest that where a single, efficient energy source is desirable or necessary for continuous demand that a FHW boiler should be employed. Further, that this source then be applied to all your structure’s heating demands with all the resources detailed within.
So, let us wrap it up by considering some common scenarios for our FHW boiler system source:
- A Central HVAC (Heating,Ventilation & Air Conditioning) System Upgrade
- Upgrade the existing FHA Furnace with an Air Handler, if desirable, or
- Install a FHW Heat Exchanger (radiator) into the existing FHA Plenum, plumb and rewire as necessary.
- Existing or planned FHA System Upgrade – Same as 1. without A/C.
- FHA installation into a seasonal, incremental, unheated area or as an expansion.
- Install an Air Handler or Unit Heater variation to suit.
- Where freezing protection is desirable, employ a Plate Heat Exchanger as necessary.
- Use a Plate Heat Exchanger to couple “incompatible” secondary heated water sources such as exterior wood & coal boilers, solar & geothermal loops, etc.
- In all cases, move to an Indirect Water Heater for efficient DHW generation.
By the way, these new high efficiency boilers do not necessarily need a chimney. Condensing Gas Boilers typically use PVC pipe for venting and Triple-Pass Oil Boilers with Pressure-fired Burners can use a direct exhausting vent kit.
Have we run you out of excuses yet?
Last Edit: 10/10/2012 pdm