Quote:
Originally Posted by Daox
I'm reading through the install manual and it says that I need a minimum of 6 vertical feet of flue. I'm guessing this is to create a proper draft?
I'm considering just adding a power vent to it so I can reuse the 4" flue (vs 5" the instant water heater requires without the power vent) I have going up the chimney and through the roof. This would avoid any cutting extra holes in the house.
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Very sorry I didn't include exhaust considerations, as they are very important...
Yes, proper draft. The amount of fuel the unit consumes when it fires is very large. If you cut corners on the minimum draft specs, you can get water vapor and carbon monoxide entering the house... both are obviously undesirable.
You also need to observe minimum stack height as it relates to the top of the roof of your house and the potential for wind swirls causing positive pressure that would impact the exiting of exhaust from your unit. Similar considerations apply to properly venting a wood stove.
An additional consideration is that the unit can create a negative pressure in the house and would pull in cold replacement air when it runs...
I picked up a more modern Bosch (LPG) at a garage sale for $35. The sizes of both the exhaust vent and built in combustion air vent on it is three inches in diameter... so a power vent can make do with smaller diameter, but passive venting really does need large diameter, careful attention to the number of elbows, etc.
If your house is still pretty leaky, you shouldn't have any problems with combustion air, but if you tighten your house up dramatically, you will need to supply external combustion air.
I don't mean to be discouraging... I'm just trying to share the lessons I have personally learned, by having done almost everything wrong initially.
Tankless heaters are a great concept, well built and very reliable. Yours should provide you with many years of reliable, economical service.
Best Regards,
-AC_Hacker
P.S.: Tankless heaters have continued to evolve since your unit and my unit were built. Two big features have greatly improved the efficiency of tankless DHW heaters, condensing combustion gases (which recovers the heat of vaporization, about 15%) and also modulating fuel consumption to match demand (very similar in effect to inverter technology that is being used in mini-split heat pumps). These features are currently found in tankless hydronic boilers, but are sure to enter the DHW market eventually.