How do I turn down the heat to my sinks and showers from a oil burner heater set at 180°F for baseboard heat?
twoboy
| 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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Replies
Diana,
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
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?
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:
http://www.crownboiler.com/manuals/content/All_Models/BDS%20Series%20%28all%20models%29.pdf
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.