Weil-McLain Aqua Plus Series 2 model 85 indirect water heater vs traditional LP water heater

srodster

I just had another post about the W/M GV90+6 boiler, and had a follow up question about using this boiler with the W/M Aqua Plus Series 2, model 85 indirect water heater. Using the indirect water heater allows for no additional venting other than the 3" PVC for the boiler. My intent was to get a LP 75 gallon Bradford water heater, but then Weil-McLain mentioned this indirect water heater that uses the boiler to heat the domestic water. Does anyone have pros or cons about it. One con I see is the boiler will now run all year for that particular primary zone. A con for the Bradford water heater is I would have to exhaust it out separately, (not particularly a big deal, but it is another hole in the roof). These would all be located in the unfinished basement. Hopefully someone has experience with these indirect systems..., I am using a well, so I need to make sure it meets those demands. I would also have a water softener on the downside of the unit, no matter which system I use.

Hot_water_fan

Indirects often, but not always, have higher recovery rates because the burner of a boiler is often larger than the burner of a standalone heater. That might matter or might not at all, depends on how you use hot water. A well doesn't seem relevant here. Overall, it's pretty much a toss up. Almost all Americans do NOT use indirects since most all Americans don't have boilers. They seem to be fine.

EdTheHeaterMan

You are not really operating the boiler "year round" like you operate the boiler in the winter to heat the home. The boiler only operates when there is a demand for heat or hot water. In the summer that demand is less than 2 hours per day. Take away the indirect ,and the LP stand alone water heater will demand the LP gas to burn more than 2 hours per day as a result of off cycle losses, while the Weil McLain boiler is off. So there, you have a demand in the summer when the Weil McLain is off. But in the winter, you will at some point have 2 demands at the same time. The boiler will have a call for heat and the water will have a call for hot water simultaneously. Two burners at the same time will burn more gas than operating only one burner at a time.

Next thing to consider is the efficiency of the burner. I will guarantee you that the Weil McLain burner will have a Higher Efficiency rating compared to a water heater tank burner. Also the Weil McLain burner is much larger than the Bradford burner, so you will recover the tank of hot water faster than the stand alone tank. To get the same "First Hour Rating" you may need to have a larger stand alone tank compared to an indirect tank. (First Hour Rating is a way to compare different types of water heaters)

Consider this. The Bradford stand alone tank has a hole in it that connects from the air intake (for combustion air) to the exhaust pipe for venting byproducts of combustion. That hole travels directly thru the tank of heated water. That hole (or pipe) is where the hot combustion gasses transfer the heat of combustion to the water in the tank. But that transfer is not one way. When the burners are off and the air moving thru those holes in the tank cools off, the heat in the tank’s water will transfer the other direction and warm up the cool air traveling thru that hole in the tank. That loss of heat (known as off cycle loss) is greater in a stand alone tank as a result of that venting hole. An indirect tank does not have that hole. It is not vented. So the off cycle loss is much less on an indirect tank. The Weil McLain boiler has the vent and if the water in that boiler gets to be room temperature while the water temperature in the indirect tank stays hot, the Weil McLain will not need to fire up to stay hot. Boiler water can be cold and that does not affect the hot water in the tank. So the down time losses are significantly lower.

PRO is lower down time heat loss and faster recovery. = more hot water when you need it
CON is you need to operate the Weil McLain in the summer, +/- Offset by the operation of the Bradford operating in the summer = Not really a CON.

GGross

Compare the warranty on the 2 tanks as well, usually the warranty on an indirect water heater is very good, many (but not all) have a lifetime warranty against defects to the original owner

Hot_water_fan

Expanding beyond this single standalone option, you can find standalone tanks with high efficiency, long tank warranties and larger burners than this boiler. They’re just not the typical option offered. 

EdTheHeaterMan

Hot_water_fan said:

Expanding beyond this single standalone option, you can find standalone tanks with high efficiency, long tank warranties and larger burners than this boiler. They’re just not the typical option offered. 

The cost difference of that Optional High Efficiency, larger burner, and different tank size, stand alone water heater compared to the one offered in the original post is something to be considered.