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Thread: Hot Water Issues (now its too hot!)- Mixer Part Question (Summer/Winter)

  1. #1
    DIY Junior Member fdawg93's Avatar
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    Default Hot Water Issues (now its too hot!)- Mixer Part Question (Summer/Winter)

    HI. I have an oil burner with hot water baseboard heat. It heats our house and hot water..with no hot water tank. Our unit is only about 4 years old but we have constantly had issues with our hot water. I've had several people look at it and they've done different things. 6 months ago they replaced the mixer (he called it a summer/winter mixer). That seemed to fix the hot water issue and we had plenty but now the issue is back. So a new guy said we didn't need it and removed it...we have too much hot water. You basically can't use the hot water unless you temper it with the cold. Which is really dangerous for my young children. So i just changed the HI temp setting to 150 and the Low to 130.

    1) Is that setting too low that it will cause damage to my unit/chimney?
    2) Do I need this summer/winter mixer back?
    3) Is there anything else I can do to adjust that water temp.

  2. #2
    In the trades Dana's Avatar
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    A low temp of 130F in an oil burner not rated for cold starts would ruin more than just your chimney, it would ruin the boiler. Consult the manufacturer's specs for minimum return-water temp- that would be the same low-limit you should run for the boiler in summer. (140F is usually "safe".) If you have a stainless chimney liner rather than terra-cotta or masonry liner, and cold-start boiler rated for 130F return water (unlikely) you can leave it as-is. But bumping up the min to 140F (or even a bit higher, with a terra-cotta liner) is prudent.

    I have know idea what a "summer/winter" mixer is. For under $100 you can buy a fully thermostatic mixing valve and set the output to 115F or whatever it takes, and you can run anything from 115F to 215F water into the hot side, and it will mix down to 115F at the output, and if the hot side goes under 115F it'll deliver whatever temperature the hot side is, with no mixing.

    For less money you can buy a tempering valve, which usually requires an input temp ~10F higher than the output temp, but works in a similar fashion.

    I'm not sure what code is in PA, but ALL hot water heaters (including tankless coils in boiler) installed in my state require either a mixing valve or tempering valve at the output as scald protection. You can set the boiler/heater temp and mixing/tempering valve to whatever you like, as long as it's capable of mixing down to at 120F or lower.

    At the abyssmally low (~40%) water heating efficiency in summer that you get out an oil boiler you can buy an electric HW heater, plumb it in series with the output of your tankless coil and put the mixer on the output of the electric tank, then just turn off the boiler for the summer. In summer the cost of heating with a $200 bargain-basement barely code-legal 0.90EF electric hot water heater at 15 cents/kwh (~$49/MMBTU) will be less than heating it with a 40% efficiency (water heating mode only) tankless coil in an oil boiler at $3.50/gallon ($63/MMBTU). If you're burning a couple hundred gallons or more from May-September it would pay for the electric HW heater well within the anticipated lifespan of an electric hot water heater.

    For anybody heating with oil in PA it's worth considering heating at least one large zone with a ductless mini-split heat pump, since the cost will be less than half that of heating with oil. A 1.5-2 ton mini-split has enough output to heat most average-sized houses at the wintertime average temp, but not necessarily at the 99% outside design temp. But if you can heat with the mini-split at the wintertime average, it's still delivering more than half the heat (at a lower cost) even at the 99% outside design temp when using the oil-burner as the back-stop. The net result is that you end up burning only about 1/4 the amount of oil, but adding about 1/3-1/2 of the oil dollar savings to the oil bill. eg:

    Say you use 800 gallons year during the heating season, and are paying $3.50/gallon for $2800 total. If you add a decent sized mini-split the oil use drops to 200 gallons/$700, but your power bill goes up by about $1000, net savings of a bit over a grand per year. A decent name-brand 1.5 ton mini-split runs about $4500, installed, a 2 ton is a few hundred more, less than $5K. If you're handy you can cut that roughly in half doing most of the installation yourself (after reading up about it), bringing in the qualified tech only when it's time to pump down the system and add the refrigerant charge.

    And, you get ultra-quiet highest efficiency air conditioning out of the deal too.

    In tight higher-R homes it's possible to get off oil entirely with these things, but most houses with code-min (or lower) windows & R-values will have comfort issues unless you start adding ductless heads, which can add up. But a 3-head 2.5-3-ton multi-split is still usually under $10K installed, and would be good enough for most homes, if the heads can be optimally placed.

    It's a chunk of change, probably way more than what's in the coin jar on your bedside table, but so is the annual oil bill. Even with the increased US production due to fracking technology, oil still sells at the world price, and the odds of heating oil dropping back to $2.50/gallon for any period of time (where it might be competitive with the world's least efficient ductless) seem really remote to me. YMMV.
    Last edited by Terry; 10-12-2013 at 10:47 AM.

  3. #3

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    It's not clear what thermostatic mixing value I'd use for the Sears 38 gallon electric water tank. The Sears plumber says he does not install that. I not sure of NJ code. A local plumber also said no. But if I buy one at Home Depot I should be able to get that installed (for a fee). What Honeywell model do I buy, as there are more than one type, right? I like the effect of added on hot water as well as safety.

    I'd be looking for the 140 (safety) down to 120 out to shower.

  4. #4
    DIY Senior Member Reach4's Avatar
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    Quote Originally Posted by Dana View Post
    I'm not sure what code is in PA, but ALL hot water heaters (including tankless coils in boiler) installed in my state require either a mixing valve or tempering valve at the output as scald protection. You can set the boiler/heater temp and mixing/tempering valve to whatever you like, as long as it's capable of mixing down to at 120F or lower.
    It would seem to be a lot better to do the mixing at the point of use. Maybe have one for a bathroom, and one for a kitchen sink if required. That would give quicker hot water. It would not make sense to supply a dishwasher with temperature-tempered water.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Where I live, you are required to use a temperature limiting valve on the outlet of the WH, and as Dana said, there is more than one type that can work. DW work better with hotter water, but having a bunch of tempering valves at points of use can get expensive and a maintenance hassle (they do wear out!). Generally, having 120-degree water max in the hot line is more than sufficient. A thermostatically controlled one is better when you have wide swings in supply water temp as it will maintain the temperature at a more stable point than a simple mixing valve. Setup a simple mixing valve in the summer with warm supply water, and you'll end up with too cool in the winter when that incoming water may be 30-40 degrees or more colder.

    Many, not all, DW have the ability to heat the water, if the incoming water temp isn't up to what it wants. You DO NOT WANT the possibility of having water much hotter than 120-degrees coming out of ANY fixture in your house. A commercial kitchen is a different thing, and they may have significantly hotter water available. To achieve that, you need something on the outlet of your WH.

    If you have easy access to the DW, you could plumb the direct, hot water to it, but that isn't a common layout. That's why many DW have the ability to heat the water, should it need it, for maximum performance. It does slow the cycle down a little, but it is MUCH safer.

    Get hotter than 120-degrees, and both the young and old can get severe burns since their skin tends to be thinner.
    Jim DeBruycker
    Important note - I'm not a pro
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    DIY Senior Member Reach4's Avatar
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    A tempering valve at a water heater is not going to be more efficient. Turning down the hot water heater is more efficient. A point of use use of a tempering valve at a tub/shower can make sense. If a required tempering valve at the water heater is mixing in cold water, I think you would be wise to turn down the thermostat. I would like to hope that you are mistaken about the law where you live. Cite?

    Hot water works better in the clothes washer, especially if there has been illness.

    Would you outlaw hot water dispensers? Would you outlaw the steam dispenser on my espresso maker? How about a coffee urn or coffee pot?

    Some fixtures have their own tempering valve. That sounds good to me.

  7. #7

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    My situation may be a bit different. No kids at risk, and no one to flush a toilet while I shower. I read if you set the tank to 140 it comes out the faucet about 130. I had the plumber not set the hot water to a low temperature when he installed the shower faucet, he warned me about scalding and I said I like steamy showers. I've had no problem adjusting at faucets.

    Is there any reason to use a temperature valve other than a scalding risk?

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    Forum Admin, Expert Plumber Terry's Avatar
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    Is there any reason to use a temperature valve other than a scalding risk?
    I have a few clients that need more water than what a 50 gallon gas water heater will provide.
    Adding a tempering valve, they can run the heater at 180 and mix it down to 120, which prevents scalding. They also make a 140 tempering valve.
    Comments I get are, "Finally I get my shower in the morning. Before the kids would run all the water out."

    Most showers are taken at 100 degrees.


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    Retired Defense Industry Engineer jadnashua's Avatar
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    I don't know if the Nashua, NH codes are online, but believe me, they do require a tempering valve AND a vacuum breaker on a WH if you want it to pass a plumbing inspection.

    FWIW, tests have shown, you want the tank at least 120-degrees. Some prefer it to be hotter to ensure you don't grow things.

    The anti-scald regs on shower valves came about because of inadequate plumbing supply systems could allow a radical temperature change in the shower output under certain conditions. Even if it didn't scald you, the knee-jerk reaction could cause other dangerous situations. There are good reasons to limit the WH output, as well as there are reasons to run it warmer than bathwater needs.

    FWIW, some washing machines, like some dishwashers, have the ability to heat the water, and that type is VERY common outside of the US, where they may only have a cold water input available. Mine has a sanitize and steam setting, should you want it for one reason or another. When I lived in Jordan for awhile, the washing machine we had would take hours to run if you wanted hot.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  10. #10

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    Terry, I'm having trouble seeing the following advantage of a mixing valve - literature says the valve is "designed to increase the amount of usable hot water by up to 50 percent". But I see no difference between mixing the tank's 140 water with cold water at the shower or at the tank with the valve. So the only thing the valve really does is prevent scalding, right? As I live alone, scalding is not an issue. Can the output water temperature be adjusted up or down with the valve if I use it and the hot water at the shower is not warm enough?

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    Forum Admin, Expert Plumber Terry's Avatar
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    Most people run their water heater between 120 and 140 degrees. They then mix that down at the tub faucet to 100 degrees.
    If you install a tempering valve at the water heater, or near the tub, then you can prevent overheating the water which can scald.

    If you were to run your water heater at 120 degrees, you would have 50 gallons of 120 degree water to use.
    If you were to run your water heater at 180 degrees, you would have 75 gallons of 120 degree water to use after running through a tempering valve.

    At was at a home this week where they had set their water heater to 105 degrees.

    Most new gas water heats have the large mark setting as 120, and then hotter than that are A, B, C, Very Hot

  12. #12

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    Terry, but in your example, if you have the 50 gallon water heater at 180, you would have 75 gallons of 120 water whether you added cold water at the tempering valve or at the tub faucet. Right? And therefore, the tempering valve's only unique advantage is that it prevents scalding at the tub. Right?

    I read OSHA that you really need the tank at 140 to better prevent Legionaire's Disease?

    So, if scalding is not a problem in my house (I live alone), then setting the tank at 140 is what I should do, and I do not need the expense of a tempering valve. Right?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    IMHO, WRONG! In the distribution system, you really don't want water hotter than 120-degrees. Have a guest over, even washing their hands...the water starts out maybe warm, then quickly gets way too hot to keep your hands under. Do that in the kitchen sink, and the jerk reaction may be to throw a plate or glass across the room. And, to answer your other question, yes, they are adjustable. This is especially necessary when you have just a simpler mixing valve. To get 120-degree water in the summertime would take a quite different mix than it would in the winter, which is one reason a thermostatically controlled valve is nicer. They both can do the same job, it's just with varying cold water, you would need to readjust periodically or accept the variation in the temp.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Forum Admin, Expert Plumber Terry's Avatar
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    So, if scalding is not a problem in my house (I live alone), then setting the tank at 140 is what I should do, and I do not need the expense of a tempering valve. Right?
    Plenty of people set their water heaters to 140. You "do" have to be more careful at that temperature.
    There are some plumbing codes that "require" a temperature limit of 120 at the tub. That's for new plumbing. Many older homes haven't been plumbed that way. Tankless water heaters come preset for 120, but can be adjusted higher. Right now I'm using a tankless set at 120.
    My mother is 96, so at her home, I installed a tempering valve for her tank water heater.

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    Terry, how important is the 140? Someone said that is really for large tanks or commercial. I will have a small 38 gallon short tank. I read the problem of bacteria is normally at the tank bottom that can run cooler. My tank is short (3 feet tall) and has a "RotoSwirl™ self-cleaning cold-water inlet tube swirls water". I use very little hot water so the water will not move and will sit in the tank a long time.

    JadNashua, many households throw plates across the room as a way of "expressing" themselves. By the way, I used to live in Merrimack. I really miss NH! Love New England. Really, no place like it.
    Last edited by netmouse; 10-14-2013 at 02:26 AM.

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