Oil Boiler and Inconsistent Domestic Water Temperature


Old 01-28-18, 07:30 PM
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Oil Boiler and Inconsistent Domestic Water Temperature

I'm hoping someone can offer my some advice. A few years ago I bought a home in the Washington DC area with an oil boiler (V8 Burnham) with 4 zones for baseboard heaters, as well as the domestic water. I'm having a problem with consistent hot water in two bathrooms by the bedrooms that are on the other side of the house from the boiler. For example when I take a shower in the morning, I have to keep adjusting the water from hot to cold to keep it from being scalding or too cold. Also, it takes forever to heat sometimes, especially if I'm running the washing machine or dishwasher. The bathroom nearer to the boiler's not an issue, neither is the sink in the kitchen. Also, this really is only an issue in winter - summer time is fine. I was thinking about adding a mixing valve to prevent scalding, but I think that may make the time lag and consistency issue worse.

Any advice for what I should do for to fix this? I've talked to a few plumbers and did some research, and found some options. First, I was thinking about installing an electric tankless water heater near the problem bedrooms, but the size I would need (5 GPM) would require 150 amps by itself - seems like overkill. I don't have natural gas, only oil and a 100 gal propane tank, and with the installation and venting costs, I don't think gas tankless is a smart option.

Another option I was thinkin I could install a regular 80 gallon tank for the domestic water. I live in a rambler with no basement, so it would have to go next to the boiler, or if I could find a small enough heater to fit in the crawlspace, that may work too.

Does anyone have experience with this and could provide some advice, or let me know if you have another option I'm not thinking about?
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Old 01-28-18, 08:44 PM
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Welcome to the forums.

Tankless domestic hot water heating is always a problem, The coils inside the boiler get crudded up and the amount of hot water delivered decreases. Then because the boiler is running high temperatures to heat your home... the domestic water comes out scalding. At the very least an anti scald water mixing valve would be a good idea.

Many people will run a storage tank off the tankless coil that stores hot water at the proper temperature. It's adjustable via an aquastat so that the boiler temps don't affect it. A tankless heater requires the boiler to run year round to create the domestic hot water. A storage tank allows the boiler to cycle less less during off season heating times. It's not the most efficient way to heat water and many times the tankless is scrapped in exchange for a standard electric water heater. That choice is based on the cost of your electricity vs the price of the oil.
Old 01-29-18, 06:00 PM
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Thanks for the quick replay, Pete. The mixing valve is looking like a smart idea - I gave myself a good reminder of that today when I turned the hot water in the kitchen on to wash my hands. I'm leaning towards an electric water tank - likely 80 gallons - to replace domestic water from boiler. I'm thinking about keeping the boiler for the baseboard heat, but I'm also not loving the idea of having another source of energy draw. In addition to the boiler, I also have central air/hvac, and a propane fireplace.
Old 02-07-18, 03:58 AM
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As @ PJMAX wrote, I would install an electric hot water tank, the size would be dictated by the available space, 30, 40,50, 80 gallon whatever size you could accommodate. I would have the boiler supply the tank with hot water in the winter with the electric as a back up for the domestic boiler coil, so you could shut off the boiler when it is not needed for home heating. The temperature control for the electric heater could be set lower than the boiler supply. I would also add the mixing valve or "anti-scald device to the tanks outlet. This would allow the boiler to provide the majority of the hot water in the winter, provide a back up source of water heater for when the boiler can not provide enough and allow you to turn off the boiler in the warmer months.. I would also have the domestic coil in the boiler cleaned if you are going to continue to use it.

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