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columbuschris

Traditional Water heater V Power vented

ColumbusChris
9 years ago

Recently had an energy audit done and our old traditional water heater is drawing barely enough. We're thinking of adding insulation and sealing the basement and attic and have been advised that our heater wont draw enough if we do this. The heater is 8 years old and runs well. Right now we've been told that we have two options a new power vent heater or to add a new smaller flue (old flue was used for furnace and water heater, now only water heater). So i wanted to get everyone's thoughts on if I should spend the $700ish for a new flue or $1600 for the new power vent hot water heater. Thanks in advance.

Comments (21)

  • cindywhitall
    9 years ago
    last modified: 9 years ago

    How long will your old hot water heater last and do you want to pay $700 for that length of time. Look at it as would you pay $700 to repair your old one?

    Also, give some consideration to the gases that are going up that flue and how safe you feel that nothing bad will leak into your living space. Make sure you get a carbon monoxide detector down there.

    But, the power vent one won't work during a power failure. I got a tankless (and a generator!). I love the never ending hot water in the winter! It was expensive though.

    I was actually able to sell my old hot water heater, it was about 8 years old. I got about $100. The buyer was converting from propane to gas and it suited his purpose because buying a conversion kit would have cost him the same amount. I don't know how many people would buy a used one in general, maybe landlords.

  • mike_home
    9 years ago
    last modified: 9 years ago

    Did the company who did the energy audit tell you your flue is too big? Are they also in the business of installing new flues and water heaters?

    What does "our old traditional water heater is drawing barely enough" and why would sealing and adding insulation cause a problem?

    I am not an expert on flues, but drawing to me means the air for combustion. The flue is to expel the exhaust gas. I don't understand why getting a hot water heater with a power vent is the solution.

    You may have a venting problem. It is very common to install a chimney liner when the furnace not longer is using the flue. In my opinion that would be a better way to spend the money rather than getting an expensive power vent hot water heater that can't operate during a black out.

    An 8 year old hot water heater has another 5 - 8 years of life. Don't throw it away and spend money on something you may not need.

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  • cindywhitall
    9 years ago
    last modified: 9 years ago

    I read this:
    Atmospherically vented gas water heaters have a major disadvantage: when installed inside the conditioned envelope of your house, they are subject to backdrafting whenever a strong exhaust fan is turned on. So atmospherically vented gas water heaters are a no-no in a tight house

    and this:
    Ironically, backdrafting may be the consequence of a more energy-efficient home. In bygone eras of cheap energy, cracks and gaps in the structure allowed continuous air exchange with the outdoors. In these “leaky” houses, negative indoor pressure would be unsustainable. In energy-efficient, air-tight homes with little outdoor air exchange, however, exhaust fans in rooms such as the kitchen and bathroom can pull enough air out of the structure to induce negative pressure. Combustion gases that would normally flow up and out of the heater exhaust vent are instead sucked into living spaces. Properly sizing exhaust fans so that the combined cubic feet per minute (CFM) of air movement complies with building safety codes can reduce the risk of backdrafting.

    If there is already a slight problem then additional air sealing might create a problem. It might be a line they feed you to increase water heater sales, or it might not be. I was told it was a safety issue and that I would need a power vent hwh when I got the air sealing done as well.

    I suggest a carbon monoxide detector get installed asap if there is not one now. I don't know if there is a way to self-test the draw (or lack of draw)

  • jakethewonderdog
    9 years ago
    last modified: 9 years ago

    Chris,

    Forget the power vent and go with a condensing tankless. The cost of the units is about the same, but with the tankless will pay back over the cost of a standard water heater in about 5-6 years.

    Use a tankless that gets it combustion air from the outside.

    On my house I had the choice of line the masonry chimney or power vent water heater. I went with the tankless and am very happy I did.

  • mike_home
    9 years ago
    last modified: 9 years ago

    Here is a link which has a good explanation about back drafting.

    Before you spend thousands of dollars on a new hot water heater read the article and do some investigation. If you have have an orphan flue then you could very well have an issue. If that is the case then in my opinion fixing the flue would be a lot easier and cheaper than getting a different type of hot water heater.

    Here is a link that might be useful: Water Heating Backdrafting

  • jakethewonderdog
    9 years ago
    last modified: 9 years ago

    You can fix the flue.. and you still have a big source of air infiltration as well as a 65% efficient or worse water heater. Keep in mind that with an atmospheric flue, hot air is going up the flue all the time - not just when the heater is on. And, when air is leaving the building that means that cold air is infiltrating, causing drafts, to replace that warm air. Why would you want to pay $700 to have a 4" hole in your ceiling for hot air to escape?

    Condensing tankless heaters pull combustion air in from the outside, then vent it back outside. You don't use conditioned air from the living space and therefore you don't have cold outside makeup air causing drafts. They are 92-95% efficient as well.

    This was exactly the same issue I had: I had replaced the furnace with a condensing furnace that vented with PVC pipe. I could no longer keep the water heater vented into the unlined masonry flue.

    The cost of the materials for the tankless was ~ $1100 the same cost as the power vent water heater that was still only 65% efficient.

  • mike_home
    9 years ago
    last modified: 9 years ago

    Conventional hot water heaters do not have a 65% efficiency rating. If they did then they would require a flue bigger than that required for an 80% efficiency furnace.

    Here is a link from ACEEE site which compares the operating costs of various hot water heaters. The operating cost of a tankless versus a conventional hot water heater is about $470 less over a 13 year period. It is not enough to pay back the cost difference.

    Here is a link that might be useful: Hot water heater comparisons

  • cindywhitall
    9 years ago
    last modified: 9 years ago

    Tankless won't pay back if you have to have it installed by a pro. It is a bit of a luxury item. I love mine ( except for that feeling of dread when there is a storm that could put the power out! But I have a generator so it's ok.) I only got it because I used the "savings" from a rebate program to pay for it and I needed its efficiency to meet the goals for the highest rebate in the program. The original poster doesn't have that bonus so I doubt tankless is on his radar. Tankless price Might be worth a check though if he is considering the power vent.

    The OP just has to decide if he wants to invest in a new vent for his old one, or put that $ towards a new one. Old one could last 2 more years, or maybe 8. I wouldn't spend the 50% to "fix" it any more than I'd spend 50% to fix any other appliance with a questionable life span. But that's me, not a big risk taker or maybe I like to justify getting new things with new warranties etc. I guess it's 6 of one or half dozen of the other. His choice.

    Mike, his old hwh probably is 65% or less efficient! I know mine was that or less and even some power vents aren't high eff, so you have to check that out too.

  • mike_home
    9 years ago
    last modified: 9 years ago

    Cindy,

    Conventional hot water heaters do not loose their efficiency as they get old. At worst it may be a few percentage points as the sediment collects at the bottom of the tank. This is a myth that the so called "energy auditors" spread in order to convince you a new hot water heater will pay for itself in 5-6 years.

  • jakethewonderdog
    9 years ago
    last modified: 9 years ago

    Mike,

    Any atmospherically vented gas appliance has a maximum efficiency of about 65% minus any standby losses which is how standard water heaters end up with an energy factor of 0.6.

    Condensing gas appliances have an efficiency starting at 92 - 95%. With standby losses, the Rheem RTGH-95DVLN, for example, has an energy factor of 0.94 (not .86 as your referenced link shows).

    A standard gas water heater will cost $277 a year vs $178 a year using the DOE information on both heaters. That's $100 a year difference.

    The cost of a standard 40 gal gas tank heater is $450 (Lowes) and cost of tankless heater is $1320 (Amazon) for 200kBTU unit mentioned above + vent kit and valves.

    Subtract the $300 federal tax credit and you now have a $570 difference that will pay back in about 5.5 years assuming gas doesn't go up in that period of time.

    These numbers work very well if it's a self install. If not, you have to be careful because installers tend to gouge on tankless installs for some reason.

    However, once installed, a tankless replacement is very fast and easy and can almost be done with a pair of channel locks and a screwdriver. (there's no big tank to wrestle out of the basement).

    There's no question in my mind that the combination of energy efficiency of the appliance, plus not having air exfiltrating the envelope has made a huge difference in my home comfort and gas bills. Yes, I have insulated and have a 95% furnace, but the original 100 year old windows and I have a $42 gas bill (budget - gas heat, water heater, dryer and stove) in central Indiana where it was -15 this year.

  • SaltiDawg
    9 years ago
    last modified: 9 years ago

    While your in Lowes pricing gas heaters, take a peak at the Hybrid Electric Hot Water Heater and its DOE sticker. ~$997 less the $300 less local rebates, including beiing exempt from Sales Tax here in MD.

    I know, noisy and not as fast recovering as NG.

    But maybe worth a peek.

  • mike_home
    9 years ago
    last modified: 9 years ago

    Jake,

    I don't want to completely hijack this tread. This will be my last post until the OP returns.

    I still disagree about the efficiency of the conventional hot water heater. But we can agree to disagree.

    There is currently no energy tax credit for tankless hot water heaters. Many energy credits ended in 2013.

    When installing a tankless hot water heater you will need to run a electric service line for power and usually you will need to increase the size of the gas service. These are additional costs which need to be added. These are not typically not DIY projects. In addition a tankless will need annual maintenance and are more likely needing repairs.

    Sit down and calculate how much gas you use to heat hot water. Then pull out your old bills when you had the old hot water tank and do a comparison. The comparison should be done in therms and not dollars. You may find some savings but they are much smaller than you think.

  • jakethewonderdog
    9 years ago
    last modified: 9 years ago

    Mike,

    There's no disagreeing on the efficiency of standard tank water heaters. It's posted right on the DOE tag that you can pull up on any heater. It's also on the link that you gave. That number is 0.60 or 60%. Forty cents of every dollar you spend is going up the flue. And that doesn't include the air ex-filtration / infiltration issue. The combustion air going out the flue is being replaced by cold air leaking around the doors and windows that then must be heated.

    The operating efficiency of the condensing tankless is 0.94. Only 6 cents of every dollar is going out the flue.

    You are correct about the tax credit, that's unfortunate. That credit makes the math work out much better. Some local areas/utilities offer a rebate or credit so worth checking.

    The other stuff is FUD though - I have fairly hard water and have cleaned my tankless twice in 5 years, both times was able to do it myself with vinegar. The nice thing is that one CAN clean it.

    Yes, they will probably need to run some larger gas line - that may or may not be significant. I think I had about 10' of 3/4" pipe on mine. Older homes that had 65% furnaces and water heaters to start with often have the gas service to supply a tankless once the furnace has been switched to a high efficiency furnace.

    Still, the installation costs can kill the deal if too much gas line work has to be done -- but it's worth looking at.

    SaltDawg: I like the Hybrid Electric units in warm weather areas. You don't want to use them in cold weather areas. The other problem that I'm seeing a lot of is reliability issues. These things should be as reliable as my 20 year old Frigidaire - because it's using the same technology. There's no damn reason that they shouldn't be able to make those water heaters reliable and for $1,000 or less.

  • SaltiDawg
    9 years ago
    last modified: 9 years ago

    Jake,

    The Hybrid Hot Water heaters work fine in a cold climate assuming located indoors in basement. Mounted in the living areas can be a problem because they are noisy - mine is located in the basement close to my heat pump. The noise from the hot water heater when operating is about the same as heat pump. (Not a problem in my basement, but I wouldn't want it upstairs in the living area.

    I still think "doing the math" for the Heat Pump hot water heater compared to a gas hot water heater would be telling.

  • jakethewonderdog
    9 years ago
    last modified: 9 years ago

    Saltidog,

    What brand / model are you using? Have you had reliability issues with it?

    I say that about cold weather climates because what you are doing during cold weather is using the heat that the primary source of heat (furnace, or heat pump) put into the space in the first place. If that's an expensive source of heat (say propane, electric resistance, or 65% gas or oil) you have significantly changed the overall efficiency and cost of running the hybrid water heater.

    For example: If you live in a climate where you heat the house 6 months out of the year and you normally use the equivalent of 150 therms a year for water heating, you would be adding the equivalent of approximately 75 therms on to your space heating load that your furnace must produce. If that heat is electric resistance, you have no net gain over a standard electric heater during that time.

  • SaltiDawg
    9 years ago
    last modified: 9 years ago

    Two things to remember about the TINY heat pump on top of the hot water heater. It only removes heat from the room to replace the BTUs that are removed from the space via hot water going out the pipe.

    Example. You go on vacation for a week. ZERO net heat is removed from the room. In other words, heat transfers from the stagnate hot water back into the room and then the heater kicks in and removes it from the space and transfers it back into the water... not free, but very inexpensive and absolutely no need for the home's heating plant to make up any heat - as I said, no NET heat loss or gain.

    Now take the case where you take a hot shower upstairs. ANY heat removed from the basement by the hot water piping remains inside the conditioned household envelope except that which exits via the plumbing drain in the shower. Also, presumably cold replacement water from the street is brought into the envelope to replace that drained water.

    I have NEVER seen a change in my basement temperature due to the heat pump hot water heater because my subterranean basement is simply a massive heat sink that resists temperature change big time. While I do remove like a pint of water from the air per day in the summer, I have never been able to measure a change in humidity - just the nuisance of having to deal with disposing of the condensate.

    You're creating an apples and oranges situation when you compare heating with gas and "pumping heat" from the room into the water. With your gas heater, the heat that 'flows' back into the room is not recycled back into the hot water heater, rather it is "replenished" by bring NG into the room and igniting it in a non-recoverable manner. The net effect is to heat the room while you are on vacation... as I suggested there is ZERO net effect with the heat pump hot water heater in my example.

    I have documented in this forum that my electrical savings for my family of two is approximately $40 per month due to the hot water heater as compared to the electric hot water heater I previously owned. I also have tried, with mixed result, to explain that taking the basement as a system and drawing a diagram show heat in and heat out of that system is helpful. Too many folks that have never owned one of these and have made false assumptions have reached conclusions that are absolute nonsense.

    My unit is a GE model... I had a compressor leak after 11 months that was repaired under warranty. Reportedly this problem was not an isolated case... and the Model was discontinued.

    If you have the time, the final math problem (actually rather simple) is to assume some water usage and calculate the enthalpy rise in the heater times the gallons and determine how much heat is being removed from the basement... that is the amount of heat that your heat pump would need to replace in the basement to maintain equilibrium.

    If I were the OP, I suspect I would opt for the Gas heater because the response time is faster, because it is quieter, and because he will not have to mess with disposing of a pint of water every day during the summer. But, I suspect that you need to caution the OP that his heater is heating the inside of the house during cooling season. :-)

    I played loose with my terminology re Heat Transfer in the above in order to attempt to better communicate the concepts - by background and education I am capable of using proper terms and terminology, but choose this approach.

  • jakethewonderdog
    9 years ago
    last modified: 9 years ago

    Saltidawg,

    I think the only part of what you just explained that I didn't take into account was the heat gain from the surrounding earth in a basement. I was aware of that factor, I just am not aware of any way to account for it --for many reasons.

    All of the other factors would likewise apply. For example: heat from the shower and drains would likewise reduce the need for the furnace to produce heat. Unless I'm not thinking correctly, in either case the net energy required for heating the water is the temperature difference between the water entering the envelope and the water leaving the envelope - during heating season.

    As a comparison to other tank heaters, keep in mind that standby losses from the tank to the conditioned space are pretty low in all cases. The worst case is a standard gas heater because it has a flue right up the middle of the tank. Most of that heat goes right on up the flue though. Contrary to marketing, the vast majority of operating efficiency gains from gas tankless come from reducing exhaust gas temperatures, not from eliminating standby losses.

    I've heard some people have an issue with the dehumidification... I wouldn't imagine that ever being an issue with a basement install though.

    Like I said, I like the idea of these heaters a lot. They can certainly be a much cheaper alternative to gas tankless.
    I just think people need to understand how they work - esp if they don't have them in a large basement. I'm sticking with my general caveat on cold weather climates.

    My hope is that they can get the reliability issues fixed fast. As I mentioned before - we know how to make these micro-heat pumps cheaply and reliably already.

  • SaltiDawg
    9 years ago
    last modified: 9 years ago

    "in either case the net energy required for heating the water is the temperature difference between the water entering the envelope and the water leaving the envelope - during heating season."

    Yes! (Also during cooling season and in between.)

    I live in MD suburbs of DC. My basement is 55 degrees year 'round. If I'm still living in seven years, I will replace my heat pump hot water heater with a similar unit.... it works perfectly this far north. :-)

    Not sure what the issue is with dehumidification. My usage is two adults and the most water removed by the unit in a day is about a pint. On the other hand, my whole home air heat pump condensate pump runs multiple times per hour during the humid summer. (Which is a good thing.)

    This post was edited by saltidawg on Sun, May 4, 14 at 9:39

  • sktn77a
    9 years ago
    last modified: 9 years ago

    To the OP: consider the following:

    1. Get a second opinion about your apparent flue issue.
    2. Be prepared for a shock when you get an estimate for professional installation of a tankless heater!
    3. You won't have hot water from a power vent heater heater if you have a power outage.
    4. Consider a direct vent water heater.

  • ColumbusChris
    Original Author
    9 years ago
    last modified: 9 years ago

    Thanks for all of the various comments. Here's some follow up.

    1) I can't install this and will have to pay someone.
    2) It is a partially orphaned flue, was originally designed for two appliances currently using 1.
    3) We rarely get power outages so i'm not as worried about that.
    4) the quote did not come from the same company that did the audit but I am getting a second quote.
    5) Tankless would require us to run a significant amount of new gas lines making it to expensive.

  • jakethewonderdog
    9 years ago
    last modified: 9 years ago

    ColumbusChris,

    I understand. My house was the same situation and there are probably many homes out there like it.

    My house was a coal furnace converted to gas. It shared the brick flue with the water heater.

    I put in a new furnace with a PVC vent and I could no longer vent the water heater in the flue.

    The reason is that the flue gases cool too much in the large unlined chimney and so they risk not leaving the home. In addition, when the flue gases cool, they condense on the brick. The resulting condensate is acidic and eats the mortar in the flue.

    Tankless was the way to go for me, but I understand it won't work in your situation. There are 0.82 Energy Star rated power vent heaters also. Don't spend the money on a power vent and not at least get an 0.82. EF heater.

    Don't spend the money on the flue though. One other advantage of using venting other than the masonry chimney is that you can potentially take the chimney down below the roofline next time you do the roof if it's not being used. It get's rid of a maintenance problem and potential source of a roof leak.

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