Tankless Water heater question

[Joe]

Mine runs on oil. I just bought the house and notice that our Weil-McLain Oil Burner and Amtrol Extrol hydronic water heating system is running every hour whether we use the hot water or not (it's not cold enough yet for the heat to be on). I assume it's running in order to keep the small water in the tank hot, is that correct? Is there anything I can do to lower the energy usuage of this unit? We take about 2 quick showers a day, run the dishwasher about every other day, launder all our clothes in cold water in a small one family house yet this unit is using about 10 gallons of oil per week. Is that normal or is there something I can do to lower the energy usage of my unit?

[flansp78]

You mention the the your boiler has a tankless coil. On the front of the coil there should be a Honeywell control. On the control are settings for Hi and Low limit as well as the diferential. Check the Hi and Lo limits. Typically, there set to Hi ~180 and low ~160 with the differential set ~20 to 25. Is your home plumbed with one zone?

[Joe]

My high is set to 190 and my low is set to 170 with a differential at

1. As far as I know my home is plumbed with one zone - how can I be sure?

[flansp78]

Move the diff out to 20 and see if you notice a difference. All the control is doing is keeping your boiler between the two temp settings.

[Joe]

I changed my high to 180, my low to 160 and my differential to 20. That means when my water temp drops 20 degrees it goes on again?

[flansp78]

Actually no....And here's why, my assumption is that you have a Honeywell L8124 Triple Aquastat.

High Limit: This is a safety limit that will shut the burner off when the boiler water reaches the high limit setpoint. The high limit has a fixed 10=B0 differential. This means that, once the boiler water temperature hits the high limit setpoint and the burner shuts off, the water temperature must drop 10=B0 below the high limit setpoint before the burner will be allowed to turn back on.

Low Limit: This is the temperature about which the boiler water is maintained if there is no call for heat. The low limit typically has an adjustable differential of 10=B0 - 25=B0. The burner will turn on when the water temperature hits 10=B0 below the low limit setting, and will run until the water temperature climbs through the differential.

Example: Low limit setting: 150=B0 Differential setting: 15=B0 Assuming there is no call for heat, the burner will automatically turn on when the water temp is 10=B0 below the low limit setpoint; in this case 140=B0. The burner will then run until it climbs through the 15=B0 differential up to 155=B0, where it will shut off. The water temp will then gradually fall back down to 140=B0, at which time the cycle will repeat itself.

[---MIKE---]

I have a similar setup. I turn the furnace off until I want hot water. Then when I turn it on it takes about 15 minutes - about 1/4 gallon to get the water hot. This is enough to do dishes etc. Showers will take an additional 10 minutes.

---MIKE---

[Joe]

So I'm basically wasting about 2 gallons of oil per day (I notice my fuel tank goes down about 10 gallons per week) by leaving my furnace on all day correct? I should be turning my service switch off at night after I do the dishes then turn it on 15 minutes before I shower in the morning and then off again until I need hot water, correct?

[flansp78]

This can be done with SOME boilers, but not all. Most Weil Mclain boilers connect their sections together via rubber O rings. Most are NOT cold start boilers and need to run or stay at temp. By turning the boiler on and off like that you would create problems and possible leaks. It's best to keep the boiler on all the time and allow it to maintain it's operating temp.

[Chris Lewis]

According to Joe :

Uh, no. Furnaces don't have pilot lights. As long as the furnace isn't being asked to supply heat, it's not consuming oil. If your water heater is part of the furnace, it will consume oil to keep the water heater hot. However, modern water heaters are pretty well insulated, and there's no way it should be on long enough to consume 2 gallons per day simply maintaining tank temperature. More like a couple gallons per month.

[flansp78]

That's a fair assesment. I filled my oil tank back on April 18th. I currently have a little over half a tank of oil. I figure at the 6 month point, around Oct 18th I'll be at or a little below a 1/2 tank.

Furnances are hot air, boilers are hot water. Both systems can run off of oil. Gas will maintain a pilot.....

You also have to understand that a boiler will hold it's temp for sometime. Weil Mclain's (Gold Series) are cast iron. As long as the sections have been brushed down on a regular basis's the unit will heat up quick, as well as the internal tankless unit, which in turn holds ~5 gal's of water.

[---MIKE---]

During the summer (June, July, August and most of September) I use about

3 gallons of oil a week by keeping the furnace off when I don't need hot water. (I have a timer on the furnace and I know that it burns about one gallon an hour.)

---MIKE---