Rannai tankless water system - 7.5 GPM or 9.4 GPM? (furnace, water tank, sink)
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Have finally saved up the money to have a Rannai tankless water system installed. Now have to decide whether to have the 7.5 Gallons/minute model or the 9.4 Gallons/minute model installed.
According to one estimator, the 7.5 GPM is really only 5 GPM because it is tested in Florida where the water is warmer to start out with than it is in North Carolina.
Three estimators all have said that either model would work for our 3 bathroom home. We have a walk-in tub in one and shower in the other two if that makes any difference. Rarely, are two of them used at the same time. The difference in price is only $200, so it's not that big a deal.
So, anyone have a 7.5 and wish they had the 9.4? Or vice versa?
I would appreciate any advice/voice of experience here.
I don't have a tankless system so I can't comment on what I would've done different. But I have to ask what the price difference is between the two. If it's not much more to have a higher gpm unit than that would be the one I'd choose. The only time the higher gpm would come in handy is if you are flowing multiple sources of hot water at the same time. A shower head typically produces 2.5gpm. A tub spout will typically double that. Due to friction loss in the piping I'd have to agree that a 7.5gpm unit will deliver close to 5gpm.
With that being said I'd have to state that it would all come down to price. As an example I have learned to always get the biggest engine available in a car. I don't see how this situation could be any different unless the price prevents you from purchasing the higher gpm model.
Yes, you could get by with the 7.5gpm unit but why have to worry about waiting to start the wash until you're done with the bath?
We just got a tankless (GE) and my wife hates how long it hates to heat up. It definitely takes longer to get hot water at the tap. If that might be a factor for you, get the most powerful thing / fastest startup you can.
If energy savings is your primary concern, take a look at the brand new heat pump water heaters. They use less energy, plus you get the benefits of a tank. Downside is recovery time / no endless supply. If it's installed in the garage, you'll get pretty good efficiency in the warmer months.
We just got a tankless (GE) and my wife hates how long it hates to heat up. It definitely takes longer to get hot water at the tap.
True but we also have a demand pump that get's the water to it's destination much quicker. It operates on a remote switch. Also, you will notice that you'll need to let the water run longer on cold days vs. warm days. Seems sort of wasteful but we love the tankless water heater (actually we have 2 and don't miss a hot water heater at all).
Total price is $2,600 installed. Have to run a gas line from the nearby gas meter and reroute water lines from water heater. This includes permits and electrician work. $200 more for the larger unit. We decided on Rennai even though there are other less expensive units, as Rennai seem to have stood the test of time and appear to be the highest rated tankless system by owners.
Not sure how the savings works out. We have an electric hot water heater and it does not produce enough hot water to come close to filling the walk-in tub. So want the endless supply so I can fill the tub and soak and so that that when the kids are all home like over the holidays, we can all shower without waiting for the hot water heater to charge up.
Plus, now we only use gas for the furnace, which means we pay $10/month for the months we don't heat and use no gas at all.
Also, in our previous home, we replaced the hot water tank about every ten years. That would be a ton of trouble here as the hot water tank is in the crawl space.
I'm a little surprised by the wait for the hot water. My understanding was that it started heating the water that passed through it so it. Perhaps if it was farther from the tankless system than it was from the hot water heater to the sink?
I would agree that the bigger the better when it comes to hot water, but wondered if there was a downside to the bigger unit.
As a homeowner who owns one of the early Rinnai tankless water heaters and as general contractor who sells, services, and installs these units, my opinion would be that this appliance is one of the smartest, most comfortable and most efficient method of heating water for domestic use.
The answer to your question is: select the larger unit if you have three bedrooms or more and two baths or more. The smaller gpm unit is ideal for smaller homes. You will not regret it.
If there is a concern from folks who have long runs from the appliance to the point of use, a small regulating pump is available that addresses this issue very nicely. I am so happy with our unit that I have installed in our rental properties, recommend it to every customer when their water heater fails, and will ALWAYS have this product in all my personal homes.
They cost two to three times the cost of a traditional water heater.
They have an extended service life and when compared side by side with traditional water heaters, the Rinnai units end up not only cheaper to purchase, but much more efficient to operate, and provide an endless supply of domestic hot water.
We saved enough money on gas use that after four years we covered the difference we paid above the traditional unit cost.
Total price is $2,600 installed... gas line, reroute water lines, and electrician work.
I'm surprised it all came in that low.
Most homes can't absorb an additional 200,000 Btu appliance like this without an upgrade in service.
(my standard gas water heater is about 35,000 Btu; furnace is 80,000)
Quote:
We have an electric hot water heater and it does not produce enough hot water
to come close to filling the walk-in tub.
oi. Is that really the expectation?
Not sure how the savings works out.
I'll be curious to see what you say after 6 mo's of living with it.
The bigger unit gives you some cushion should the efficiency drop off or it's not quite as powerful as promised. Most of those GPM rates only cover a 30-35 degree temperature increase. Your incoming water would have to be 85-90 degrees to get the max flow.
Look at the Rannai website for the specs on each unit to find the chart that shows the GPM against the temperature lift. Right now the incoming water temp is 55 degrees. Let's say you want the water heated to 120 degrees, the 7.5 GPM unit gives you about 4.5 gallons per minute and the 9.4 GPM unit barely gives you 5 GPM. During the winter you won't be able to run multiple showers at the same time with the smaller unit, which could appear undersized when its time to sell the house.
A note regarding the advice on adding a circulating loop - check the warranty. It usually cuts the warranty period way down if you add one of those. Make sure to have your plumber include cutoff valves to allow for the annual cleaning/maintenance routine. If you do that yourself you can save some money. Hire a plumber and you'll pretty much lose any savings from going tankless. It's likely that you won't see enough of a savings to pay for the conversion costs either way.
I'm surprised it all came in that low.
Most homes can't absorb an additional 200,000 Btu appliance like this without an upgrade in service.
(my standard gas water heater is about 35,000 Btu; furnace is 80,000)
I'll be curious to see what you say after 6 mo's of living with it.
Thanks. I'll ask about whether the need for an upgrade in service. Have had three estimates from plumbing companies and no one has mentioned that.
I'll let you know after six months. We bought the home recently and I was really looking forward to that walk-in tub. Disappointed that we aren't able to fill it. Use it like a shower now.
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Rinnai Tankless Water Heaters ALWAYS!!
