Tempering tank & Tankless water heater?

I do not think so. When the tankless senses flow it turns on, With no need or limited need to fire your unit shouldn't be able to modulate that low.

STIHLY DAN said:

I do not think so. When the tankless senses flow it turns on, With no need or limited need to fire your unit shouldn't be able to modulate that low.

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Motor7 said:

But unless a hot water tap is open there would be no flow through the tankless. If I send the heated water from the tempering tank to a hot water tank(or any insulated tank) how does that help or hinder the tankless? I am trying to grasp the whole concept here so bear with me............

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Yeah, I could be wrong but since there is only water flowing through the tankless when someone uses water, I don't see why it wouldn't work. You are basically just preheating the feed water to the unit. Do the tankless units not sense water temperature? If they do, I would think that it would just not fire up if the water is already hot, or if it did, just for a bit...

brenndatomu said:

Yeah, I could be wrong but since there is only water flowing through the tankless when someone uses water, I don't see why it wouldn't work. You are basically just preheating the feed water to the unit. Do the tankless units not sense water temperature? If they do, I would think that it would just not fire up if the water is already hot, or if it did, just for a bit...

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Use a small circulator, like a Laing, and circulate the water from the furnace through the tempering tank. Then just pull your cold feed from the tempering tank to the tankless. Works great, we do it all of the time. HVAC contractors are also doing the same thing with geo, tempering tank, and a tankless.

Make sure your tankless can "accept" pre-heated water. Some units can't. Something to do with the incoming temperature and flow sensors are on the supply side of the heat exchanger, and get can fried if they are hit with hot water.

brenndatomu said:

Yeah, I could be wrong but since there is only water flowing through the tankless when someone uses water, I don't see why it wouldn't work. You are basically just preheating the feed water to the unit. Do the tankless units not sense water temperature? If they do, I would think that it would just not fire up if the water is already hot, or if it did, just for a bit...

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Depends on the capability of the tankless. Say you have 100* water going to the tankless and it is set at 125* out, the tankless may not be able to modulate down that low to only increase temps by 20/30*. Could have lots of short cycling and inconsistent hot water. For example my brother has an older tankless that cant supply consistent hot water to his kitchen sink because there is not enough water flow through it, but if he runs another sink at the same time it works great.