From time to time I’ve seen references here to “high efficiency water heaters.”
Is there such an animal?
I’ve just been through the Bradford White models, and none seem to go above 80% “recovery efficiency.” (Some don’t give such a figure.) The lowest figure given is 76%
I’m wondering if there are, in fact, “high efficiency” hot/warm/cold* water heaters, or if folks are assuming that draft inducer = high efficiency.
The US Dept of energy says this:
“Rating Efficiency
“Once you have decided what type of water heater best suits your needs, determine which water heater in that category is the most fuel efficient. The best indicator of a heater’s efficiency is its Energy Factor (EF), which is based on recovery efficiency (i.e., how efficiently the heat from the energy source is transferred to the water), standby losses (i.e., the percentage of heat lost per hour from the stored water compared to the heat content of the water), and cycling losses.
“The higher the EF, the more efficient the water heater. Electric resistance water heaters have an EF between 0.7 and 0.95; gas heaters have an EF between 0.5 and 0.6, with some high-efficiency models around 0.8; oil heaters range from 0.7 to 0.85; and heat pump water heaters range from 1.5 to 2.0. Product literature from manufacturers usually gives the appliances an EF rating. If it does not, you can obtain it by contacting an appliance manufacturer association (see Source List).”
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* Per regulations recently adopted by the Equal Opportunity for Water of Varying Temperatures Commission {G}]
I don’t know about yours, but my church isn’t a hotel for the holy, it’s a hospital for sinners
Replies
http://www.njenergystarhomes.com/html/builder/tutorial/H-E_WaterHeating.html
http://www.energystar.gov/ia/new_homes/features/HighEWaterHeating1-17-01.pdf
http://www.nol.org/home/NEO/loan/improve/whstand.htm
If you plan to install a gas storage water heater, you must purchase a unit with a minimum efficiency rating of 0.60 to receive a loan. Click here for more information.
http://www.socalgas.com/residential/savemoney/conservationtips/waterheat.shtml#listefficient
Also you might want to look around AO SMith web pages. I think that I have seen some that where spec'd for heating along with HW service and also had an AFUE rating.
Thanks for the links."High Efficiency" seems to be more of a marketing term than description.The Bradford White and AO Smith sites use different units of efficiency, but within the range of water heaters at the two sites, there is very little difference between the various models and venting systems.OTOH. since I can't find a definition of the energy efficiency units, I don't know how significant the difference between, say a .58 and a .64 "Energy Factor" is.But I think that people tend to assume the "power vented" water heaters are "high efficiency" in the same way draft induced and draft assisted furnaces have significantly higher efficiencies than natural draft furnaces.I don't know about yours, but my church isn't a hotel for the holy, it's a hospital for sinners
Sojourners: Christians for Justice and Peace
Well the first two links include this and show a picture with a blower."The most commonly used types of water heaters today are gas and electric storage units. Figure 1 shows possible improvements to gas storage type water heaters including more efficient burners, better flue design, and low input pilots. Since more heat is transferred to the water with these models, combustion gases are exhausted at a lower temperature and can be vented with PVC pipe through a wall (similar to a clothes dryer)."So from these I figure that if it is rated to use a PVC vent then it is "high eff". Now they probably require a blower to vent with the low temps. But there might be some with blowers that don't have low temp exhaust.Here is a more complete list of hf units.http://www.aceee.org/consumerguide/topwater.htmWhat is interesting is that the 50 gal units use the same or less amout of gas than the 40 and 30 gal units. Of course that is based on their "standard usage" used for the test.You might want to look around the aceee or contact them to see if they have more details on EF testing.http://www.energyright.com/waterheat/faq.htmNow this has some general FAQ's and at the bottom it gives a ASHRAE standard for testing.And a link to DOE proceedures. However, that link is dead and redirected to a search engine.http://www.eere.energy.gov/menus/search.htmlUseing - water heater energy factor - as the search terms give some links that might be helpful, but I did not go through them.
My understanding is that the water heaters with the blowers can use plastic vents because they are pulling large amounts of room air into and mixing them with the flue gases so they are much cooler.My new combustion analyzer allows me top measure flue gas temps, so next time I run into one, I'll check out the temps in the internal flue and the flue after the blower.But in looking at the actual specs, there is very little difference in their rated efficiencies, so I'm beginning to suspect the inclusion of a blower isn't significant from an efficiency point of view.I looked at the specs of about 20 different water heaters yesterday and use of descriptive words like "high efficiency" in the product descriptions bore little relation to actual rated efficiencies.I don't know about yours, but my church isn't a hotel for the holy, it's a hospital for sinners
Sojourners: Christians for Justice and Peace
There is an employee of State water heaters that sometimes post here about tankless units and has written a comparision about them and tank type.http://www.stateind.com/new/Tankless_WhitePaper.pdfI think that he use WRHOOVER as a username.Try contacting him.
Bill,
I did a combustion analysis yesterday on both a Rheem power vent, 40,000 btu 40 gal tank, and a Richmond natural draft 40 gal, 40,000 btu.
Neither was drafting properly (see the pic below for the backdrafting problem with the powervented) and the natural draft water heater had a lower draft reading.
I don't think those draft problems were having a significant effect on the flue temp readings however.
For the powervent, the flu gas temps in the tank's internal flue were 430° and a flue temp after the draft inducer of 161°; the natural draft had readings of 421° and 345°.
Thus the powervent is pulling a lot more room air into, and mixing with, the flue gases than the natural draft.
I forgot to get the efficiency ratings from the tags, though.
OTOH, I think this shows that the ability to use plastic flue with powervents is not because they are heating the water more efficiently.
I don't know about yours, but my church isn't a hotel for the holy, it's a hospital for sinners
Sojourners: Christians for Justice and Peace
Forgot to attach the pic ....I don't know about yours, but my church isn't a hotel for the holy, it's a hospital for sinners
Sojourners: Christians for Justice and Peace