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  1. #1

    power vent water heater and HVAC impact

    I am looking for a new water heater and my existing HVAC/water heater is a Rheem 80% and BW water heater vented through what i would say is a traditional metal chimney. the house is 12 yrs old and I am looking to pro-actively replace the water heater. The difference in price is signficant between a traditionally vented WH, and a power vented water heater. Assuming sometime in the next 5+ years I replace the HVAC system will the move to get a chimney vented WH now impact the HVAC Upgrade?

    I know many newer HVAC high effieciency systems vent through a PVC pipe and eleminate the chimney (which I like), so would putting a Water Heater with chimney vent be a bad move? I have read the power vented models are more expensive and dont last as long and have many more complex components.

  2. #2
    Join Date
    Dec 2008
    Location
    Buffalo NY
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    3,124
    If your water heater is vented through a metal chimney such as a b- vent you will be fine with that and can skip a power vent. Pewter vent heaters have there place but I would avoid them if you can.


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  3. #3
    Join Date
    Feb 2010
    Location
    In a boiler room
    Posts
    7,142
    Power vent models are no more efficient than a chimney vent model.

  4. #4
    Join Date
    May 2012
    Location
    Upper Michigan
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    3,589
    Quote Originally Posted by chuckcrj View Post
    Power vent models are no more efficient than a chimney vent model.
    Beat me to it, they all are the same basically. I think they are more like 60% eff correct me if I'm wrong.


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  5. #5
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,311
    Consider an instant water heater. Cost a little more than conventional power vented some even use PVC pipes.

  6. #6
    Join Date
    Jun 2007
    Location
    Minneapolis, MN
    Posts
    735
    At conventional gravity (atmospheric) vented water heater will last about 10 years on average. The "combustion" efficiency is in fact about 80%. This number is based on ambient air temperature and stack temperature to keep it simple. A typical power vented water heater will us PVC to vent the by-products of combustion to the outdoors instead of a traditional chimney, saving the builder money. That is really the only advantage of this appliance and if you have ever had to replace the blower on a power vented water heater, you know the cost can be a problem. The power vent draws the hot gases from combustion mixing them with conditioned inside air to enable the use of PVC venting material.

    If you want high efficiency water heating-above 86% combustion efficiency you will have to buy a condensing water heater, either tank-less or tank type. We use more tank-type condensing water heaters such as Polaris or Vertex as we have many big tubs to fill and often use them for combination space heating and DHW.

  7. #7
    Join Date
    May 2012
    Location
    Upper Michigan
    Posts
    3,589
    I have always been told 60% on draft vent, never really tested or anything.


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  8. #8
    Join Date
    May 2012
    Location
    Upper Michigan
    Posts
    3,589
    Found this
    http://aceee.org/node/3068


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  9. #9
    Join Date
    Jun 2007
    Location
    Minneapolis, MN
    Posts
    735
    The article is useful but misleading. And energy factor of .60 is not 60% combustion efficiency (40% of the available heat from combustion going up the flue) nor is it thermal efficiency (the heat transferred to the water). It is akin to the AFUE used for space heating equipment. We have tested many atmospheric water heaters with electronic gas combustion analyzers. 80%.

  10. #10
    Join Date
    Feb 2010
    Location
    In a boiler room
    Posts
    7,142
    Thermal efficiencies (heat actually transferred from the fire to water) run around 69 - 72%. It is impossible to reach 80% without condensing at least some of the flue gases.

    The combustion efficiency calculation on a combustion analyzer means nothing useful. It has too many assumptions. Sometimes making an appliance more thermally efficient actually has made the CA read a slightly lower efficiency!

  11. #11
    Join Date
    Jun 2007
    Location
    Minneapolis, MN
    Posts
    735
    Quote Originally Posted by chuckcrj View Post
    Thermal efficiencies (heat actually transferred from the fire to water) run around 69 - 72%. It is impossible to reach 80% without condensing at least some of the flue gases.

    The combustion efficiency calculation on a combustion analyzer means nothing useful. It has too many assumptions. Sometimes making an appliance more thermally efficient actually has made the CA read a slightly lower efficiency!
    I believe the question was of combustion efficiency and the confusion was over CA. I find great use for the CA nearly every day. Though thermal efficiency can't be measured in the field it pays to know you stack temperatures (one aspect of the CA test). Suffice to say, atmospheric water heaters, including power vents are not efficient. We use a lot of condensing water heaters.

  12. #12
    Join Date
    Jul 2009
    Location
    Columbia, MD
    Posts
    4,054
    thermal efficiency can be measured in the field. It is also the only true efficiency reading.

    My customers always loved when i showed them what their furnace was producing when i arrived and what it did when i left, which also improved on their energy bill.

    output/input = thermal efficiency

  13. #13
    Join Date
    Jul 2009
    Location
    Columbia, MD
    Posts
    4,054
    I would stick with ol' fashion water heater.

    If something were to break on the power vented one, it cost about as much as a new water heater.

    keep it simple.

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