Efficiency of Utilities: Difference between revisions
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*Electric water heaters (tank) are about 95% efficient, while gas are about 63% efficient [https://smarterhouse.org/water-heating/replacing-your-water-heater#:~:text=The%20minimum%20efficiency%20of%20electric,to%20the%20high%20operating%20costs.] | *Electric water heaters (tank) are about 95% efficient, while gas are about 63% efficient [https://smarterhouse.org/water-heating/replacing-your-water-heater#:~:text=The%20minimum%20efficiency%20of%20electric,to%20the%20high%20operating%20costs.] | ||
*Efficiency factor (EF) considers standby loss but not distribution loss. Gas is 60% and electric is 90%. Tankless gets gas EF up to 82% (standby efficiency), but that doesn't consider distribution loss. Electric is 100% efficient to begin with, so standby would be near perfect efficiency. If you are at the point of use - you are close to 100% efficiency. | *Efficiency factor (EF) considers standby loss but not distribution loss. Gas is 60% and electric is 90%. Tankless gets gas EF up to 82% (standby efficiency), but that doesn't consider distribution loss. Electric is 100% efficient to begin with, so standby would be near perfect efficiency. If you are at the point of use - you are close to 100% efficiency. | ||
=Standby Losses= | |||
*Standby losses for water heaters are about 1000BTU/hr - [https://forum.heatinghelp.com/discussion/108652/hot-water-heater-standby-loss-cost-how-figure] - or about 300W! | |||
*1993 average was 1200kWhr/year! [https://inspectapedia.com/plumbing/Hot-Water-Heater-Standby-Losses.php]. Equivalent to 140W. That is more reasonable. | |||
=Cost Efficiency= | |||
*Electricity costs about 2x as much as gas for the thermal content - but it's lower cost if you use a heat pump. | |||
=Expected Hot Water Heater Usage= | |||
*Shower x2.5 - 6 minutes - 15 minutes | |||
*Dishwasher - 3 times per week - or 3/7* per day - of 4.5 gallons - with 0.3 gpm water use - 15 minutes of how water at low flow. But only about 7 minutes of that. | |||
*Washing hands and brushng teeth - 6 minutes *2.5 - 15 minutes | |||
*Total - 37 minutes of hot water - or 1 kWhr with a 1.6 kW water heater. | |||
=Conclusions= | |||
*Point: there is absolutely no case for gas heat with advances in heat pumps! Unless you are attracted to having a gas system in your house for some other reason. One advantage is that gas can be available even if electric dies - so gas is useful from a backup perspective. But backup heat is done better via pellet stove - cheaper and more decent(ralized). | |||
*There is little case for gas water heater with point of use electric heaters! Which can be as efficient - as they save both standby | |||
*On-demand heaters, when used with low flow - can easily use less energy than tank heaters lose in standby! In fact, we are using 1kWhr - about | |||
Revision as of 17:51, 21 February 2021
- Heat pump is 3x as efficient as electric heat.
- Point of use is 27-50% more efficient than tank water heater [1]
- Electric is 2x as efficient as gas - this one says 74% vs 40% efficient.
- induction is 20-25% more efficient than electric cooking - with induction at 90% and electric at 65-70% - [2].
- Electric water heaters (tank) are about 95% efficient, while gas are about 63% efficient [3]
- Efficiency factor (EF) considers standby loss but not distribution loss. Gas is 60% and electric is 90%. Tankless gets gas EF up to 82% (standby efficiency), but that doesn't consider distribution loss. Electric is 100% efficient to begin with, so standby would be near perfect efficiency. If you are at the point of use - you are close to 100% efficiency.
Standby Losses
- Standby losses for water heaters are about 1000BTU/hr - [4] - or about 300W!
- 1993 average was 1200kWhr/year! [5]. Equivalent to 140W. That is more reasonable.
Cost Efficiency
- Electricity costs about 2x as much as gas for the thermal content - but it's lower cost if you use a heat pump.
Expected Hot Water Heater Usage
- Shower x2.5 - 6 minutes - 15 minutes
- Dishwasher - 3 times per week - or 3/7* per day - of 4.5 gallons - with 0.3 gpm water use - 15 minutes of how water at low flow. But only about 7 minutes of that.
- Washing hands and brushng teeth - 6 minutes *2.5 - 15 minutes
- Total - 37 minutes of hot water - or 1 kWhr with a 1.6 kW water heater.
Conclusions
- Point: there is absolutely no case for gas heat with advances in heat pumps! Unless you are attracted to having a gas system in your house for some other reason. One advantage is that gas can be available even if electric dies - so gas is useful from a backup perspective. But backup heat is done better via pellet stove - cheaper and more decent(ralized).
- There is little case for gas water heater with point of use electric heaters! Which can be as efficient - as they save both standby
- On-demand heaters, when used with low flow - can easily use less energy than tank heaters lose in standby! In fact, we are using 1kWhr - about