Abandoning Summer/Winter Boiler Domestic Water Tankless Coil

EdTheHeaterMan

random12345 said:

What I would like to do at some point is find a way to control the aquastat via wifi. So basically the boiler would be cold start, and the aquastat would be disconnected from the burner, but if I want to take a shower, I push a button on an app on my phone, and the aquastat I already have "turns on" and operates as normal with a high limit of 190, diff 20. The tankless coil would be operating more like a tankless water heater. I'm wondering if I can do this with a Honeywell T775 maybe connected to a wifi smart plug. Should pay for itself in a few months over the Summer.

That would be ideal. Push a button 15 minutes before you need to take a shower. Push a button 15 minutes before you want to do laundry, wash dishes, or get a 2 minute use of hot water to wash your hands.

But you can get a point of use instant water heaters that run on electricity. That would be more cost effective for the short usage, and you don't need to remember to push a button 15 minutes ahead of using the hot water. But the American way of instant gratification means that you have 40 or 50 or 75 gallons of hot water on stand by in a tank in the basement so we don't have to wait. What are you willing to give up in order to reduce your energy usage? You get what you pay for. ...And after you design this great idea, and install it, how long before you are tired of the inconvenience, so you just turn the whole thing off and go back to the way it worked before you implemented your invention.

Mr Ed.

random12345

With my electric rates, I don't believe an instant electric water heater would pay off. Nice idea though. It's just something I'm been thinking about. I'm not even sure it's feasible. The inconvenience is clear, but if I can make it work with an inexpensive controller and plug for a couple hundred bucks to save maybe $1k/yr...I think that's worth it. But I don't know if it will, so for now it's on the back burner.

EdTheHeaterMan

random12345 said:

With my electric rates, I don't believe an instant electric water heater would pay off. Nice idea though. It's just something I'm been thinking about. I'm not even sure it's feasible. The inconvenience is clear, but if I can make it work with an inexpensive controller and plug for a couple hundred bucks to save maybe $1k/yr...I think that's worth it. But I don't know if it will, so for now it's on the back burner.

Changing from a boiler that maintains 160°F temperature to a cold start boiler will save $1000.00 in one year's time, sounds ambitious. Are you currently spending over $10,000.00 per year on fuel? (that's about 2500, gallons per year) My experience is that swapping from a tankless coil to an indirect with cold start boiler maxes out at about 10% savings if you are lucky. This might be a 5 year savings plan. Not a 1 year savings plan.

random12345

Boiler is usually set at around 165-185, $4/gallon heating oil, and assuming I burn a couple hundred fewer gallons a year by doing this gets me close to $1k. I think this would be a lot more efficient than an indirect because the boiler never has to maintain that tank temp, so the standby losses are basically entirely eliminated. I could be totally wrong though. If you think this is wildly optimistic then you're probably right. I trust your experience more than my own wild guesses.

EdTheHeaterMan

@random12345, it appears that we have hi-jacked this discussion. Sorry for that, however, I believe the OP received the needed information. The best way to determine any oil usage in real time (since delivery amounts and dates are not so accurate in determining daily usage) is to place a meter on the oil valve. This Hour meter will act like an odometer. By taking daily readings and multiplying the valve open time by the firing rate of the burner, you will get an accurate gallon per day number.

The amount of hot water you actually use can be measured by a water meter on the hot side of the water heater (I'm not recommending this) then taking temperature readings of the hot water as it is used. Eventually you will see that the actual water used and the cost to heat that water will all boil down to 1 BTU = 1 pound of water changing 1°F (no pun intended)

And since the amount of time the average home actually uses hot water is less than 2 hours per day, then anything over actual usage of hot water would be considered standby loss. That is the amount of burn time needed to maintain the boiler or tank temperature for the other 22 hours each day. With on demand tankless water heaters, those standby losses are minimized to what is left over in the heater after the hot water use is finished. The rest of the day the tankless water heaters get cold and has no loss. With tankless coil boilers you will find the greatest standby loss. With direct fired water heaters, the standby loss will be somewhat less (basically maintaining a lower tank temperature than the Summer/Winter boiler temperature). The indirect tank that is not connected to a vent comes in a second place on stand by loss, far more efficient than tankless coil boilers and direct fired tanks, but more standby loss than tankless on demand water heaters.

random12345

EdTheHeaterMan said:

@random12345, it appears that we have hi-jacked this discussion. Sorry for that, however, I believe the OP received the needed information. The best way to determine any oil usage in real time (since delivery amounts and dates are not so accurate in determining daily usage) is to place a meter on the oil valve. This Hour meter will act like an odometer. By taking daily readings and multiplying the valve open time by the firing rate of the burner, you will get an accurate gallon per day number.

The amount of hot water you actually use can be measured by a water meter on the hot side of the water heater (I'm not recommending this) then taking temperature readings of the hot water as it is used. Eventually you will see that the actual water used and the cost to heat that water will all boil down to 1 BTU = 1 pound of water changing 1°F (no pun intended)

And since the amount of time the average home actually uses hot water is less than 2 hours per day, then anything over actual usage of hot water would be considered standby loss. That is the amount of burn time needed to maintain the boiler or tank temperature for the other 22 hours each day. With on demand tankless water heaters, those standby losses are minimized to what is left over in the heater after the hot water use is finished. The rest of the day the tankless water heaters get cold and has no loss. With tankless coil boilers you will find the greatest standby loss. With direct fired water heaters, the standby loss will be somewhat less (basically maintaining a lower tank temperature than the Summer/Winter boiler temperature). The indirect tank that is not connected to a vent comes in a second place on stand by loss, far more efficient than tankless coil boilers and direct fired tanks, but more standby loss than tankless on demand water heaters.

You have no idea how much I enjoy taking measurements, and now that you've put this idea into my head, I'm not sure I'll be able to stop myself from doing it...This would only work during the non-heating season. During the heating season, I would need to have a way to correlate oil usage with heating and non-heating calls to the burner to get hot water oil usage. I already thought of doing what you suggested at one point, but never went through with it:
https://fuelminder.biz/mazoutman/mazoutman.html
https://flows.com/hot-water/

I will keep everything you've told me in mind, but for now, I'm sticking with the TC. So many other projects need doing at the moment. I still have to insulate the rest of my steam pipes in the boiler room and the hot water pipes as well...

bburd

There is one additional factor to the calculation of oil use from run time data and nozzle size: oil pump pressure.

Oil burner nozzles are rated at 100 psi. Some more modern, efficient burners (Riello for one) are set for higher oil pressure, and a chart or rating factor must be used to determine the actual firing rate.

EdTheHeaterMan

bburd said:

There is one additional factor to the calculation of oil use from run time data and nozzle size: oil pump pressure.

Oil burner nozzles are rated at 100 psi. Some more modern, efficient burners (Riello for one) are set for higher oil pressure, and a chart or rating factor must be used to determine the actual firing rate.

I agree. This is why I used the term "Firing Rate" and not "Nozzle size" in my description of how to measure fuel usage. Another important factor is the type of oil valve you have on the burner. There was a time before Pre-purge and Post-purge primary controls, when you could accomplish the same thing with an old school 3 wire primary control. You would use a Delay Opening Oil Valve. If your system still has one of those valves, you would also need to have a cycle counter and deduct [the delay time of the valve multiplied by the number of cycles] from the total time the valve was energized.

But if you were going to the trouble of measuring the VALVE ON time with an hour meter, you probably would also spring for a new oil valve.

john123

During the summer ----so what about closing the DHW side of one of the newer 95% mod con gas boilers (in addition to the heating side too). I'm thinking that if you only use the heating section of the boiler for a couple of months in the winter every year, perhaps you could save the wear and tear on the boiler and the regular annual maintenance and do it every 2nd or 3rd year. And use a tank type electric DHW water heater in the summer???? I'm thinking that the old cast iron boilers were good for 40? years but the new efficient boilers don't seem to last that long and you could extend the newer boilers' lifetime with this procedure.

How long do you think a 2023 mod con boiler with proper maintenance will last (with parts availability!) if it used 12 months of the year for both heating and DHW?

Can someone tell me how the DHW circuit actually works in a modern mod con boiler --please. I'm guessing that when a DHW calls (a hot water tap is opened)---- for DHW priority ----a set of 4 valves open and close and send the boiler supply water directly to the flat plate heat exchanger (and block the route to the radiators) and the return from the flat plate heat exchanger is piped into the return for the boiler which likewise is blocked from receiving water from the return from the radiators. Assuming a LLH or CST's the system water could continue to swirl around the heating pipes pushed by the system circulator and the boiler pump/circulator would send the hot water directly through the flat plate heat exchanger. Any comments would be greatly appreciated.

If in the summer, the heating side of the boiler were turned off and only the DHW side was used, would the return water would be a little hotter than usual and outside the normal condensing range? and therefore the boiler creating the DHW would be less efficient in the summer than in the winter?