Tankless Water Heater inadequate
I have a Bosch AquaStar 125 gas water heater we have used for about two years. We live in N. Minn. and find the output of the water heater inadequate, both in temp and flow, particularly in the winter. It looks as if the plumber installed it correctly. I understand the water heater can only raise the water temp only so much and the water (right out of Lake Superior!) is probably too cold. Is there a legitimate fix for this problem, short of buying a higher output water heater. We are considering tearing it out and going back to a traditional tank setup. Has anyone had this problem? Has anyone installed a water tank to temper the water before it is heated? Would a loop-back scheme, feeding some heated water into the cold supply, resolve the problem? As you can see, I am not a plumber. Any help you can give would be appreciated.
Bob
Replies
Add a preheater to the system and supply more information about the water supply. Too many unknowns to SWAG a guess.
Pump? Capacity? Pick up? Line size? Filter system? Distance of lift? Water temp? Rated rise of the heater? Rated GPM?
And anything else you can offer.... (CC#'s. Passwords.)
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A lot of people love those units but have problems when there are several water users simultaneously--you start a load of laundry and then hop in the shower while someone is washing dishes.
Check out the performance of the unit according to the manufacturer--how many gallons per minute can it flow and what number of degrees can it raise the temperature? That info should be in their specs. Then see if your unit is doing that--measure the incoming water temp and the hot temp you can get with a couple of fixtures running at one time. If it's not up to spec then you may need a repair or replacement. Since a plumber installed it for you maybe they should check it out as well (especially if they supplied it).
If it's working right and you need more water, you may want to install a bigger unit. I'm not familiar with the model you mentioned but a couple of manufacturers make high-volume units for households with five teenage daughters. Or, go to a storage heater. It's easy to compare energy costs on them, and if you have the floor space for a tank then maybe that's the way to go.
A tempering tank might be a reasonable solution. Doesn't have to be heated, just in the heated space so that the cold water can warm up a bit. Recirculating water through it from the water heater would be better, but that requires the complexities of a pump.
Another option is to install a small tank heater, set to the lowest temp, ahead of the tankless.
But at some point you have to question whether you might as well go ahead and install a high-efficiency tank heater in place of the tankless.
warm up the lake..a few little thermonuclear devices will do it..and a free supply of fish for life..
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Like the other poster said, you need to get data on how many gpm you are using at one time, and the incoming and outgoing temperature of the water through the heater to see if the unit is heating as much as the manufacturer specs.
Here's how. Turn on the items you are trying to use at one time. If it's just one, like the shower, turn on just that. Using a bucket and a timepiece, measure the time it takes to fill a known amount. Calculate your gallons per minute. Add these up if you use more than one fixture at one time.
Turn on another faucet, hot only, nearby till it's just barely running. Let it run into a cup with a thermometer. You want it running enough so you are getting hot water, but not so much it adds any appreciable load to the water heater. A dribble is enough. Put a thermometer in the cup and keep checking it until it stops rising. Note the temperature. Then, turn everything off, and turn on the cold water at the same faucet full. With the thermometer and cup you now can measure the cold (incoming) water temperature.
Compare the temperature rise and flow to the manufacturer's specs.
Your other question, about a recirc loop -- it won't work. You'll get hotter water, but a lower volume in an exactly proportional amount. You can do the same thing by using less water at one time.
If you already have a heater and like it you don't necessarily have to remove it to install a standard unit. If you have the space you could install a standard unit ahead of it to temper the incoming water. It wouldn't need to be set very high at all. For example, if you wanted you hot water 10° hotter than it is now, and your incoming water were at 45° today, you'd only need to set the tank to 55°. Of course, when it ran out, you'd be back to where you started, so you may want to set the tank higher, at least to room temperature. They probably can't be set even that low, anyway.
If your tankless worked when new but doesn't now it could be several things. Among them would be hard water.
We have had the same unit for 4 years and the water is too hot in the winter to use just hot. The winter incoming water temp is 58f. With your water coming straight out of the lake its going to be very cold! Perhaps you could have a "storage" tank that holds the water at room temp before you use it, this is providing your unit is working correctly and the water is just to cold from the getgo.