Excessive heat loss on S120?

As a homewoner who has an indirect...

The specs for my W-M indirect (actually Triangle Tube) claim 1/2 degree loss per hour. I have not actually measured what I get. By itself this number means nothing. Consider that the heat loss depends on the temperature difference between the water temperature inside and the air temperature outside the heater. And this is not specified. If it is 95F outside in the summer and I heat the tank to only 115F inside (I do not do this) that is only 20F difference. But if it is 40F outside and I heat the water to 140F inside, that is 100F difference. Surely the heat loss will be different in each case.



This is further complicated because the domestic hot water tank is surrounded by the outer boiler water tank that is hotter than the desired domestic water temperature, at least until the aquastat is satisfied. After that, the water in the outer tank (that is insulated from the surrounding air) cools down, but until it gets down to the aquastat temperature, keeps the domestic water hot for a while.



The installing contractor installed heat traps in the hot and cold water supply pipes to the heater. Actually he could not help it because the cold water comes up from the floor to the top of the heater, and the hot water descends from the top of the heater back to the floor. But the pipes do rise an extra foot over the heater. Even so, I noticed that those pipes were hot, so I put 1/2 inch black foam insulation (from big box store) on those pipes until I had enough that I did not feel the heat anymore. I also put that insulation on the pipe from the P-T relief valve. Since I did not measure the heat loss before or after, I do not know for sure if that made any difference, but it made me feel better. More important, I think, is that I put similar insulation on the pipes to and from the boiler that carry much hotter water to heat the hot water in the tank.



It is my impression that the heater comes on about twice a day, and that is with the hot water I use for my morning shower (I like it hot). Otherwise I do not use much. I do not know if it comes on in the middle of the night or not. So perhaps it comes on three times a day. But it never runs more than 10 minutes.

I have not thought much about oil.

I have a gas-fired mod-con boiler and an indirect. For the purpose of heating domestic hot water, it does not matter much about its being a mod-con, since it does not modulate for this, and it condenses a little when starting up, but not otherwise.



I use it all year long for domestic hot water. The reason the efficiency is good is that it runs cold start. I understand that this is less satisfactory for oil burners. The volume of the heat exchanger (which is the entire boiler in my case) is only about 3 quarts, and the boiler input can be as high as 80,000 BTU/hour, so that heats up very fast. There is also about 12 feet of 1-inch pipe in the circuit to the indirect and 6 gallons in the jacket of the indirect. As soon as the water temperature exceeds the temperature of the water in the indirect tank, the heat is being used to heat the domestic water. So the burner does not run much at all except when it is heating the domestic water. Also, once the aquastat in the indirect is satisfied, the circulator in that circuit continues to run for about two minutes to flush the hot water from the boiler into the indirect. So there is very little waste.



I am not sure things would work as well with an oil burner run as cold-start because I understand there are maintenance issues when doing this. And for boilers with large water volumes, the waste would be more, bringing the larger volumes of water up to temperature.