Aquastat Settings, and Hot Water Question

15 years ago

I recently purchased a home with a new yorker oil boiler(95' I've been told) that has a coil for domestic hot water, or summer/winter hook up and old cast iron radiators for heat. When I moved in the aquastat settings were the typical 180 HI, 160 LO settings. When we purchased the home we had a mixing valve installed before closing to prevent scalding. When trying to take showers, typically the water starts out hot, then goes to lukewarm-cool for some time, then after 5-10 minutes of the cool-lukewarm water, returns to hot again. Could this be due to the mixing valve, or settings on the boiler itself?

We had an HVAC tech out to clean the boiler, and while here he adjusting the aquastat settings to what looks like just under 150 on the LO. He left the HI unchanged...and said adjusting the LO would cut down on oil usage. I should mention that we have used 3/4 of a 250 gallon tank of oil in 3 weeks, which seems like a lot...but it has also been a very cold 3 weeks in PA. After the HVAC tech adjusted the LO setting, the showers got even colder. Without really knowing what I was doing, I adjusted the mixing valve higher which helped somewhat, but not completely.

Is there anything I can try, or adjust to help with this hot water problem? Should I move the LO setting back to 160 degrees, and keep the mixing valve high? Also, does the use of 3/4 of a 250 gallon oil tank in 3 weeks seem typical? Or is that a large amount? We usually have the thermostat set at 66 during the day, and 63 at night. The area that the thermostat is located does seem slightly colder than other parts of the house due to old drafty windows, which we plan to replace shortly. Would that help?

I should also mention that it appears the DIFF setting on the aquastat is set somewhere between 10 and 15. Is this okay? I know there are a couple questions here, but any responses would be very appreciated. Thanks

Sort by:Oldest

Comments (3)

baymee
15 years ago
Sometimes the lo limit is set to 150 for cast iron radiators, but this won't save you a cent in oil during the winter. It will just take longer to heat your house. In summer, you can set it back to 140.

In PA, limestone areas will coat the inside of the coil with calcium and you'll have the problem you describe. Water starts out hot and gets cooler, but it stays cooler during the shower, unless the boiler kicks in. You MAY have such a coil problem.

You might also have a mixing problem, but I'm leaning towards the coil. Mixing valves also get calcium and are cleaned by soaking in vinegar.

Your differential is OK and you can set the lo limit back up to 160.

Your oil usage is caused by lack of insulation, drafty windows, and other such problems. Your unit is new enough that it should produce 85% combustion efficiency.

Oil will produce 140K btuh of heat per gallon, minus your efficiency loss at the burner. It takes longer to heat up the house at 150 water temp. than at 160, so the burner just runs longer. Running longer does give greater efficiency than start and stop, but maybe 1%.

I think turning the aquastat back up to 160 will help out, but I'm leaning towards a blocked coil, which can be acid cleaned. The problem can only be solved permanently by using a water softener.
toonice
Original Author
15 years ago
baymee,

Thanks for the response, I appreciate it. I thought that the coil might potentially need cleaned, so I asked the HVAC tech about this. He said that by looking at it, there are no signs of calcium or any build up. He said something about being able to tell either at the joints, or one other way which I forget...but said it looked to be in good shape and wouldn't recommend cleaning it yet...mainly b/c of the cost to do so...something in the $200 range. The mixing valve is brand new (3 weeks old) so I don't think it will need cleaned yet. You're right about the efficiency, I was told is was mid 80's. I will adjust the lo limit back up to 160 and see if this helps. It's funny b/c he actually told me the opposite of what you said. He said by adjusting it to 150 on the lo, it wouldn't run as long. It's possible he meant it wouldn't stop and start as much. If the problem persists, would you recommend going against the word of the first HVAC tech and having the coil cleaned anyway?

Also, we do plan on having some new windows installed...actually getting an estimate later today. In addition, would it help out if I better insulated the basement around the boiler? There are two doors leading to the outside and a crawl space under the porch where the oil tank is located, neither is insulated well and as such, the basement isn't very warm. If I insulate those doors, and can keep the basement warmer, will the boiler have an easier time keeping the water temperature up? Thanks.
Related Professionals
New Canaan Solar Energy Systems · Old Saybrook Solar Energy Systems · Paradise Solar Energy Systems · Saratoga Solar Energy Systems · Cypress Home Automation & Home Media · Detroit Home Automation & Home Media · Pittsburgh Home Automation & Home Media · Safety Harbor Home Automation & Home Media · Surfside Home Automation & Home Media · Wheaton Home Automation & Home Media · Grand Haven Home Automation & Home Media · Burlingame Electricians · Canton Fireplaces · East Orange Fireplaces · Lake Ridge Fireplaces
baymee
15 years ago
At 150, it won't run as long in the summer because the boiler maintains that setting, but in the winter, it runs above 150 normally, and it just takes longer to heat up the house. with cast iron rads, some people keep it at 150.

The only way he can tell if there's calcium in the coil is to remove the water line and look inside. But, if you have calcium deposits on your faucets, etc, it's safe to say you have it. If not, then not. Do you have crusty white deposits on the faucets? Your neighbors would know if there is calcium problems in your area.