I'm in the beginning phase of researching the possibility of replacing my standard 50 gal LP fired tank type with a tankless water heater. I'm wondering if any of you fine folks here have done such a conversion or have any good reasons why I shouldn't. I believe I have a decent handle on sizing the unit properly. My biggest concern is whether or not I will be able to use my existing 3" class b vent... TIA
Some HE units use PVC as intake and exhaust. Most that I've seen give you the required venting specs. HTH
seems to me the power vented models use pvc and the direct vent models use stainless of some variety. looks like it leaves no hope of reusing existing b vent.
I am looking into one too. I want enough flow for two showers and a wash machine at once, no existing vent.
I'm in no rush as mine is still functional, just lacking performance. I may hold out till spring if I can handle the complaining...
Smoke show, I deal with tankless water heaters quite a bit and will try to give you some good advise. The major concerns are basically these: 1) there are a couple good manufactures out there and there is allot of junk. 2) the units do as they state but they must be sized correctly for flow and temp rise. 3) the units must have the gas supply lines sized correctly. This is the thing I see screwed up the most by far. Jack the Knife, you need to come up with two basic numbers for your needs. 1) total maximum water flow in gallons per minuet for all desired appliances in operation at the same time. 2) temperature rise required for your water. This formula will give you a ballpark figure: (GPM * 8.34) * 1.2 * temp rise * 60 = BTU per hour input required example: Let's say your showers are using 2 GPM and the washer is 5 GPM. So total flow would be 9 GPM. Next we will figure you need to achieve 120* and your incoming water temp may be as low as 50* in the winter so we need to achieve a 70* temp rise. Our calculation would then be (9*8.34) * 1.2 * 70 * 60 = 378,302. BTU per hour input heater capability. As you can see the numbers can get out of hand pretty easy. However also keep in mind that at that flow rate you would completely empty a 40 gallon water heater in 4.5 minuets. To put it in another perspective for this scenario, if you took 15 minuet showers and the washer used 30 gallons of water you would probably need two 50 or three 40 gallon water heaters. Now this could be achieved with two medium tankless units cascaded together. But is not waiting 15 minuets to start the washer worth 2-4 thousand dollars more cost? If you were willing to wait to start the washer until after the showers one unit would suffice. Tanked heater; Pro's: inexpensive, short term reserve flow capacity. Con's: higher operating cost due to constant heat loss, low total long term capacity of less than 1 GPM. Tankless heater: Pro's: you pay to heat only the water you use, much larger long term capacity of 3-6 GPM. Con's: larger up front cost, less instant flow capability. In easy to understand terms the real advantage to a tankless is if we compare a standard 40 gallon tanked to a standard 175K BTU tankless we would get: 30 minuet capacity - tanked 61 gallons / tankless 120 gallons 1 hour capacity - tanked 83 gallons / tankless 240 gallons 2 hour capacity - tanked 126 gallons / tankless 480 gallons The real disadvantage: instantaneous flow - tanked virtually unlimited / tankless 4 GPM 4 minute flow - tanked 10 GPM / tankless 4 GPM 10 minuet flow - tanked 4 GPM / tankless 4 GPM There are a few other possible issues that may dictate what unit to use such as a recirculating loop or a very low flow requirement. Sorry to ramble but if you have any questions I will try to answer them.
We were a family of six and never had hot water issues. We all knew, only draw hot water from one thing at a time. Never was a concern.
We are considering a tankless for our other place in northern Michigan. It doesn't get used a lot in the winter, so it would save a lot of time draining the present 40 gal LP unit. What is involved in winterizing a tankless? I can have the place drained and ready to freeze in about ten minutes, except for draining the tank. That takes most of an hour, including dragging a hose thru the house. Besides, the current unit is really old.
Not really. The only main difference would possibly be incoming temperature. Around here some areas of municipal water supply may be as shallow as 5-6' leading to incoming temps as low as 38-42*. Where as a well at 150' may never see below 52*. Of course incoming water quality is a concern, but as long as it is decent it is no more picky than a tanked heater. The only concerns would be brackish water, hydrogen sulfide, high chloride levels, or a PH outside of say 6-7.5. Issues such as these would push me away from a copper heat exchanger. Location can make a very big difference as someone in Minnesota may see incoming water temps in the 30*s where as someone in Texas may never see temps below the 70*s.
You would be surprised. I consulted on a house a couple years ago that they were running out of hot water with three 50 gallon water heaters. There was 5 kids and the two parents all taking showers in the morning plus starting two loads of laundry and dishes all in less than 2 hours. Total calculated hot water demand was well over 300 gallons in 90 minuets! We installed three cascaded Rinnai RL94i's at 200,000 BTU each giving about 15 GPM @ 70* temp rise. They were on well water and the well was tested at 30 GPM.
Basically, do not try to do electric tankless. Let's put it this way, that same 4 GPM @ 70* rise would take a 40+KW heater drawing about 170 amps at 240 volts!
Do you know anything about the point of use electric tankless, say for an upstairs bathroom sink that is a loooong run from the hw heater? Seems like a long draw to get the hw there for just a few seconds of use. I have two bathrooms back to back and was thinking of one unit to service both, just the sink.
