Tankless Hot Water - Its cycling on and off every 45 minutes with no demand.

[stejus]

We had oil burner serviced and it's louder now so I hear the burning coming on and off. I decided to track it for 4 cycles and here's what I found.

This is with no heat or hot water being drawn. The temp in the basement is 70 degrees and the outdoor temp is around 60. The burner is 81% efficient according to his paper work. The burner is a Beckett with .75 GPH nozzle.

On average, it will cycle on every 45 minutes and run for roughly 3 minutes. The water temp on the boiler starts at 190 degrees and ends at 200 degrees.

Doing the math, it cycles 32 times or 90 minutes in a 24 hour period to keep the water hot with no draw. That's 1.125 gallons a day with no draw! Back in the summer I tracked it based on oil deliveries and I think it was around 1 gallon a day with hot water usage.

Does this sound right for this time of the year. My concern is something doesn't look right and it will only run longer in the colder months.

Thanks guys!

Steve

 

[Nofossil]

Sounds like maybe you've got pretty strong draft and the chimney is pulling enough air through the boiler to cool it down. I'd also consider running it 20 degrees cooler, especially during the summer. That's a lot of standby loss.

 

[stejus]

Sounds like maybe you've got pretty strong draft and the chimney is pulling enough air through the boiler to cool it down. I'd also consider running it 20 degrees cooler, especially during the summer. That's a lot of standby loss.

Hey nofossil - Draft figures are Breech Draft -.04 and Over Fire Draft -.02. I have no ideas what these mean, they are just recorded on the paper work he left. I had a dual chimney cap installed in May, I dought this has anything to do with it seeing it ran less in the summer.

 

[WES999]

That's a about how much oil my burner used ( older unit not that efficient), it would run about 1.2 hrs/day with a .90 GPM nozzle = 1.08 gal/day.
My temp was set lower 160 -180, I think. I have since switched to a electric water heater, I think is is a lot cheaper to run than oil.
You can read more about it here: https://www.hearth.com/talk/threads/39434/
AS nofossile said maybe lowering the temp may help.
You are spending about $80/ mo for DHW an electric would probably be about $20/mo.
Oil DHW is probably the most inefficient way to heat.

 

[stejus]

Sounds like maybe you've got pretty strong draft and the chimney is pulling enough air through the boiler to cool it down. I'd also consider running it 20 degrees cooler, especially during the summer. That's a lot of standby loss.

I noticed the draft door (not sure what it's called) swings open and closed a lot. This is the tee area where it comes off the furnance and into the liner. When it's done swinging, the door is left open about half way. There seems to be a weight on the door to balance it. Could this be the reason theres too much draft?

How do I adjust the temp hi and low degrees to have it cycle on at 160 and off at 180?

 

[stejus]

Well, I think I may have stumbled across something. I looked at my aquastat settings and the LO: was set to 180 and the Diff was set to 10. I can see having it set this way because the HI was set to 200 degrees. I guess the rule of thumb is to set LO to 20 less than HI.

I don't use my furnace for heat much these days with the stove in place. Last night I turned the settings down to LO: 140 and HI: 160. I guess my furnace has just become a DHW on demand heater.

I haven't tracked the cycle yet but I suspect it will cycle a whole lot less now. I took a shower this morning and there was plenty of hot water.