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Community and Q&A

Tankless gas water heater?

runner9 | Posted in Energy Efficiency and Durability on

I’m considering switching to gas tankless hot water. I know there are articles here and from Consumer Reports, both a few years old, saying it’s not worth it-is that still the case?

What about in my situation? Current atmospheric tank vents to a chimney. Upper portion of chimney is leaking, best solution is to remove it, don’t want to rebuild it. It only supports that 22 year old hot water tank.

I don’t think I have a good location for a direct vent tank, near an outside wall and away from doors/windows/furnace vent. Direct vent is also not very efficient, and there’s little knowledge/stock that I can find around here. Alternatives are power vent and tankless. Iffy on power vent using a motor, being loud, etc. Had stopped considering tankless for above reasons but am thinking I should consider, it might be only a few hundred $ more than power vent, both installed.

We’re in our 30s, planning to live in this house until we’re very old, so any changes needed to gas and water pipes would be a benefit for decades down the road if we stick with tankless.

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  1. GBA Editor
    Martin Holladay | | #1

    You wrote, "I don't think I have a good location for a direct vent tank, near an outside wall and away from doors/windows/furnace vent." That observation raises the question: Do you have a good location for a tankless heater? A gas-fired tankless heater still needs to be vented.

    Assuming that you do have a location for a tankless heater, it may well make the most sense for your house. If you have a problem with an existing chimney, or if you lack a good location for a tank-style heater, then of course these factors may trump issues like installation cost. Your individual circumstances matter.

    If your question concerns the payback period for the incremental cost of a tankless water heater compared to a tank-style heater, that payback period depends on your fuel cost and family size.

    If you have access to natural gas rather than propane, your payback period will be very long. (Natural gas is cheap.) Your payback period will be shorter if you have a large family (or if your family uses lots of hot water) than if you have a small family (or if your family uses less hot water.)

  2. runner9 | | #2

    Thanks Martin. We're on Natural Gas, already only using 0.9 MCF to 1.1 MCF on average in the warmer months. One young child, no more on the way, all clothes washed on cold, etc.

    Several years ago I had a few estimates for tankless and they they were what I thought was really high. Each guy that came struggled a bit on where to put it and left me after the experience with 2 possibly locations. Each has wall space, but not floor space. Therefore I believe a tankless would fit but a tank style would not.

    I think I need to have a few companies actually send someone out, look at what I have and give their opinion on cost and feasibility of direct vent, power vent and/or tankless.

  3. davidmeiland | | #3

    Curious about the chimney? If you are going to remove it, will you have to patch the roof, and if so, can you just install a roof jack for a gas vent, and re-vent a standard water heater there?

    I had a propane tankless water heater for several years and eventually removed and sold it. The wait time for hot water is longer with tankless, unless you go with some type of storage or recirc setup. I have not paid much attention to changes in tankless, because electric is dominant here and almost everyone has a standard tank. If they have solved the wait time issue, it might be worth considering. With our unit, it took an extra 6 seconds for the hot water to arrive at the fixture, and if you shut the water off and then restarted it, you waited another 6 seconds (such as when rinsing dishes).

  4. runner9 | | #4

    I could replace the brick chimney above the roof with just a pipe, but would really like to eventually remove the entire chimney all the way to the basement and reclaim the space in the kitchen on the first floor.

    As I think more about it: are power vent gas hot water tanks really bad, or just not really good? Will the interior air used for combustion and the noise be different than a HE gas furnace?

  5. davidmeiland | | #5

    A power vent water heater will use indoor air for combustion, which can be an issue if the house is tight enough or if there are negative pressure issues causing backdrafting. You can't really put one in a closet without making allowances for combustion air, but perhaps you can put one in a large basement without much concern--you really need to evaluate the specifics of every installation and make sure it's going to work. Were there any signs of backdrafting with your current water heater?

    When you say "HE" I take that to mean a direct vent appliance that is using outdoor air and plastic pipe for the flue, in the 90% efficiency range. Power vent is different and probably in the 80% efficiency range, no different than natural draft.

    Not sure what electricity costs you, but what about a heat pump water heater? Depending on the space you have, it might be worth considering. You could skip the flue altogether.

  6. runner9 | | #6

    Thanks for the responses. This is and will be in a basement, a few small walls but nothing closed in. Current furnace is American Standard Freedom Series 95% efficiency single stage.

    I'm only trying to compare noise and amount of indoor air used for combustion between the two, I realize the difference in efficiency.

  7. Expert Member
    Dana Dorsett | | #7

    The instantaneous fuel & combustion air draw of a tankless with two showers running is on the order of 125-150,000 BTU/hr.

    An atmospheric drafted tank is about 35-40, 000 BTU/hr.

    The heat loads of most houses are less than 50,000 BTU/hr, but the furnace could be anything. At typical oversizing it could be nearly as big as a tankless heater. The American Standard Freedom 90 condensing furnaces run anywhere from 38,000 BTU/hr to 113,000 BTU/hr, and unless you tell us there's no way to know which one yours is.

    The noise of a tankless is a lot LESS than any hot-air furnace, but still a bit louder than your refrigerator. But since it's in the basement it's not likely to be much of a disturbance, if that's what you're really going to do.

    If you don't need a tankless for space-saving reasons it's rarely worth the trouble. A condensing tank HW heater with a ~76,000 BTU/hr burner like the AO.Smith Vertex will deliver comparable or better efficiency to a 199,000 BTU/hr condensing tankless, and is more than enough hot water heater for most 4-5 person families, and would certainly cover your family's needs:

    A 76,000 BTU/hr stainless condensing tank type HW heater like the HTP Phoenix Light Duty can easily last as-long or longer than a tankless, but with fewer quirks and less maintenance. If you're in it for the long term you might consider one of those.

    When the condensing furnace craps out you could replace it with a hydro-air handler running off a 76,000 BTU/hr condensing hot water heater and still have plenty of hot water capacity in most homes.

  8. runner9 | | #8

    I called three places today, nobody has experience with direct vent. All three are coming out Wednesday to look at what I have, decide if they think a power vent is possible, where run the vents, etc.

    I'll look more but a condensing tank seems to be a lot more expensive for very little fuel savings, from what I've read thus far.

    Our current furnace is model AUH1B080A9421AA, I don't know the BTUs.

  9. Expert Member
    Dana Dorsett | | #9

    You pay more in maintenance with a tankless than you'd save in fuel savings- it's not about the fuel savings. It's about reliability. The recommendation for a stainless tank is predicated upon your stated plan " live in this house until we're very old...", not the net present value of future fuel cost savings. A stainless condensing tank with a 76,000 BTU/hr burner is lower maintenance than a tankless, has none of the quirks of a tankless and should last longer than a tankless. The fact that it's also at least as efficient as any tankless is a secondary factor.

    Also, unlike most tankless installations, with a 76,000 BTU/hr burner you probably won't have to upgrade the gas plumbing OR the meter to accommodate the burner. Tankless units typically run 140,000 -199,000 BTU/hr burn rates at the high-fire end, and usually need either higher gas pressures (regulated down at the tankless) or a dedicated " or 1-1/4" gas line run straight back to the meter to work reliably.

    The typical blower on top of a cheap power-drafted hot water tank is about as loud as a hair dryer, and considerably louder than most tankless units.

    If I'm reading the part numbering scheme correctly the "...080.." in the middle of the number indicates a fuel input rating of 80,000 BTU per hour,
    which means it could heat my antique sub-code 2400' house at 0F...

    ... twice!! :-)

  10. runner9 | | #10

    Thanks Dana. Maybe I wasn't clear, I/we have decided against a tankless. If a power vent can be vented correctly I think that's the way we'll go. The issue is if all three companies come tomorrow and say there's no way to put in a gas power vent tank, then what?
    I've looked at little at electric, but that seems like a last choice. I don't know what other choices there could be that make sense except tankless or fix the chimney and keep it.

  11. Reid Baldwin | | #11

    Dana, would happen to have any cost data on the Phoenix Light Duty water heater you mention? Pairing that with a hydronic air handler is an intriguing heating option.

    The HTM website says "sealed combustion vents in inexpensive 2” PVC, CPVC or ULC S636 pipe up to 100 equivalent feet" so it solved the OPs venting issues.

  12. runner9 | | #12

    OP here, my venting is still up in the air as far as I'm concerned. My basement is roughly 22x25. The back wall is an addition without basement, the only part that isn't has a window and is very narrow. The wall closest the hot water tank has the outside door and then stairs straight down.
    On the side the hot water tank is on the furnace already vents and on the inside there is the electrical panel. I don't think there's enough room to vent it there but it will be great if there is.
    A good location both inside and out is the other half of that shorter outside wall, on the other side of the stairs. The issue is just getting the venting there, there's also an I beam running the length of the house. I don't think the vent can go up, then down, then back up. If it could I'm all set. Otherwise I don't really see how it could work unless it was a very short tank and it went under the top of the stairs to the other side and then out. Only other option I could think of is the other 2 walls but the other long wall has the same I beam issues and the other short wall is all the way across the basement, which doesn't have good ceiling height to begin with. Only other possibility I've thought of is up through the insulation in the outside wall and then it could be 3 feet higher than the furnace vent, but that would mean opening the wall.

  13. user-2890856 | | #13

    HTP Phoenix light duty should be able to be had for around 2,100.00 from a wholesaler . If you provide your location I could check pricing in your area and extend a courtesy of you purchasing at my cost on a COD basis .

    It is correct that the unit would have no problem providing hot water to a coil at a later date for an air handler . This would also allow you to use ODR to vary the water temp to closely match the changing loads throughout , quite possibly the entire heating season , shoulders and all .

  14. rocket190 | | #14

    That Phoenix unit is interesting. Something I wish I knew about when I replaced the furnace in my house. Could have replaced the electric water heater and furnace at the same time.

  15. runner9 | | #15

    Thanks all for the advice. After considering three companies proposals, and not finding anyone with experience doing direct vent, we're having an AO Smith 50 gallon 40K BTU power vent (Model GPLV 50) installed this Friday.

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