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How do I turn down the heat to my sinks and showers from a oil burner heater set at 180°F for baseboard heat?

Diana Atwell | Posted in General Questions on

I have a Crown Bahama oil boiler that was installed in 1990. I have baseboard heat, so the boiler is set at 180°F.

The problem is that the same temperature water goes to my showers and sinks. I have to warn everyone to prevent scalding.

I would think that there would be separate zones, one for baseboard heat and another for sinks and showers, but no one seems able to give me an answer. I would love to be able to have this fixed.

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  1. GBA Editor
    Martin Holladay | | #1

    You need to install a tempering valve (also known as a thermostatic mixing valve). A tempering valve automatically mixes a little cold water with your hot water supply to make sure that the water that is delivered to your showers and baths is at a safe temperature.

    Your current situation is dangerous, and does not meet code requirements.

    For more information, see these documents:

    Thermostatic mixing valve

    Safety Thermostatic Tempering Valves

  2. David Meiland | | #2

    Hopefully the original plumbing is separated cleanly, so that one pipe goes to a circulator and then to the radiators, and another pipe goes to the fixtures. It that's the case, it will be easy for a plumber to install a tempering valve on the pipe that goes to the fixtures. Got any pictures of the boiler room and piping?

  3. Expert Member
    Dana Dorsett | | #3

    The Crown Bahama uses an isolated tankless coil for the domestic hot water- running potable water through the heating system would have long-since destroyed the boiler by now! See figure 7 page 6:

    It's doesn't really matter where the tempering valve on the output goes as long as it's before the first branch in to a hot water tap or mixer.

    It's unlikely that the baseboards ever REALLY need to run at 180F, and the high-limit on the boiler can be safely turned down at least a bit. As long as the water returning from the baseboards entering the boiler stays above 140F the boiler will tolerate it, but the overall hot water heating capacity may suffer a bit. With a tankless coil only the initial slug of water comes out at the full boiler temp- the heat transfer capacity of the coil isn't unlimited, and the water temp will drop to a lower temperature that is a function of incoming water temp and flow rate, and at high flow rates, a function of the BTU-rate of the burner. In most cases you'll still get pretty good hot water heating performance without compromising the boiler with a too-low return water temp if you crank the high-limit down to 160F, and the low-limit to 140F. A tempering valve is still a good idea, but the scald risk comes down from 3-alarm crazy to something less scary when you lower the boiler's high-limit to 160F.

    If the heating system is chopped up into a bunch of zones turning down the temp 20F may cause the boiler to short-cycle when only the smallest zone is calling for heat, but htat may already be happening.( If it's a single zone that's not enough of temperature change to make a difference.)

    On a totally different note, at the 5-year recent history price of oil, heating a large zone of the house with a ductless mini-split heat pump is extremely cost-effective- costing half or less per delivered BTU than getting that heat from the boiler. Even at an up front cost of $4-5K 1.5-2 ton cold-temperature mini-split, it will often pay for itself in under 3 years, but in some areas it may take 5 (depending on your actual heating season, and electricity rates.) Anybody looking to kick or reduce their heating oil habit is urged to take a closer look at this technology, now that it has evolved to where it can deliver reasonable efficiency and has reasonable capacity at +5F/-15C or even colder.

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