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Old 03-13-2018, 10:56 AM
taylorjm taylorjm is offline
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Join Date: Sep 2016
Location: Saginaw, Michigan
Posts: 261
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J-mech and Rescue are spot on about the 1/2" pex. By the time you put a fitting INSIDE the pex. your really restricted. Compared to 1/2 copper that doesn't have a fitting inside it. If you don't have enough flow, the burner won't kick on.

Oak, you are talking about a combustion blower on a furnace, those are usually on the 80% efficient ones. When you get to the 90% condensing and use pvc pipe as exhaust, there's an exhaust blower that has to run longer than 1/2 second before the burners kick on. A furnace that exhausts with pvc will usually have a 20-30 sec purge before the burners kick on because that's required to verify enough venting to not push carbon monoxide back into the house. Now figure, this tankless is going to consume about 3-4x as much as your furnace, and you don't want that to not vent properly, so the exhaust blower has to run at least a few seconds before the burners kick in. How many seconds? I honestly don't know. But I'd worry why my furnace running at 60,000btu needs a 20 second purge, and your going to run a 200,000btu tankless heater that would only need 1 second purge. I'd guess it's going to need at least 10 seconds, but again, I am not positive. Maybe they are different technology now, could be, I don't know, but I'd want to check that before buying one.

Now, as far as being efficient. You really need to look long and hard at this one. People think if they aren't storing hot water, they are saving money. There's tons of studies out there that say you need at least 10 years to break even with a tankless because of the higher up front cost. That's assuming you don't have to repair the tankless. If you need to vent with pvc, like I did, a tank style water heater will run you about $800-900. A high end tankless could run double that. So, you need to make up about a $900 upfront cost in gas savings. Many people have had tankless installed and said their bill didn't change. So your going from running 40,000btu tank style, keeping water warm all the time, to a 200,000btu tankless that runs when you need it. I guess it just depends how much water you use, how soon you will recoup the cost. All I know is when those burners kick on, and you hear the whooooosh of all that gas being burned....ya gotta wonder how much it's going to save you! All depends on your situation.
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