After ours was installed I stumbled across a company that makes an all in one unit called Eternal Hybrid (link below). You may want to contact them and see about getting the energy efficiency specs to go that route. I think Navien also makes an all in one system now too. I would think either company would be able to give you more accurate energy specs and better answer your question. The other thing to keep in mind is that without the loop (& pump), you are in effect wasting gallons of water waiting for the hot to kick in--think showers, sinks, etc. How much does the water wastage cost in terms of both water & sewer bills + the unnecessary waste of a resource? In addition to washing machines not pulling enough water through at a time to trigger the heater and then remain on long enough to actually get the water down the line to the machine, some dishwashers are having problems too. Here is a link that might be useful: Eternal Hybrid Hot Water Heater Site

The time it takes for the hot water to get to your faucets or shower is related to the distance the water has to travel from the hot water source to the sink and the diameter of the hot water building supply pipe (typically 3/4 inch) as well as the feeder pipe to the sink (typically 1/2 inch). A 3/4 inch pipe holds about 8 ounces of water for every 3 feet of pipe. So if your tank (or tankless) unit is 90 feet away from a faucet, you would have to push out about 1.8 gallons of cold water (plus whatever water is in the feeder pipe, a 6 foot section of 1/2 inch pipe holds about 8 ounces of water) before the hot flows. A typical sink faucet will run at 1.5 gallons per minute maximum flow rate - so you are looking at over 1 minute to get hot water in this scenario. With tankless units, there is also a small delay between the time the unit senses water flowing through it (which triggers it to fire) and the time the unit heats the water up to the set temperature. There are 3 ways you can eliminate the long delay. The first is to put a hot water source (tank or tankless unit) closer to the sinks that are far away from the current source. The second way is to use point of use hot water generators under key sinks that you use. These POU units are very small tanks or tankless units designed to service just once sink. The last method is to install a recirculating loop where you constantly circulate hot water through the hot water building supply. I have a Rinnai tankless system that we installed in the basement directly below the master bathroom. From the time I turn on a shower or sink, hot water is flowing within 10 seconds. That was the good news. The bad news was that the kitchen sink and 3 other sinks that we use often are over 120 feet away from the Rinnai tankless units. Just before we finished the house, we discovered that it was taking several minutes to get hot water at the kitchen sink - and that was unacceptable to us. I wound up installing a recirculting loop. This was not the way I would have preferred to do it, but space and venting in the basement on that side of the house was an issue. You could just live with the delay you have - 1 minute isn't that bad. If you decide to fix the delay, I recommend posting some details on the plumbing forum and seeking advice on how best to correct.

I have a Triangle Tube Series 50 (45 gal.) in a 2,000 sf house with 2 bathrooms. My plumber said I should put in a smaller unit and I wanted a bigger one. We compromised on this unit, because he said a bigger one would consume a lot more energy. I take a 25 min shower with a 5 gpm shower head, and I get enough hot water from this unit, but it took some doing. The first thing I would suggest is to turn the temperature on the water heater all the way up. We have an L-shaped ranch with the water heater on one end of the house, and the master bath on the other (over an unheated crawl space). So we need to keep the water very hot to get enough hot water at the bathroom. The hotter the water is, the more cold water you'll mix in, and the longer your hot water will last. Despite this, I was still running out of hot water after about 15 min. As my shower valve doesn't have a volume control, I put a small valve on the shower arm which allowed me to slow down or shut off the water when I was soaping myself. This allowed the hot water to recover a bit before I finished my shower. The real breakthrough came last summer though, when I had a new boiler installed. The installer told me that the circulator pipes between my boiler and water heater were only 3/4", when they should be 1 1/4". He also set up the new boiler so that the water heater gets priority over heat to the house, and the boiler automatically heats up to 180 degrees whenever the unit calls for more hot water. Now I have plenty of hot water for a 25 min shower followed by a shave, even without turning the volume of hot water down during my shower. I think you should be able to get enough hot water out of this unit provided you use it to its full capacity. You may need to have someone do some work on your boiler though. One rule of thumb I live by, is to never let a contractor tell me how much water or hot water I need. Aside from this, do you have separate shower valves for your 2 shower heads, and are you satisfied with the water flow? Many newer shower valves limit the flow to 2.5 gpm or less. You can check your actual water flow with a 2.5 or 5 gal bucket and a stopwatch. If you're getting enough flow out of the shower arms, but not out of the shower heads, there are some places that sell shower heads with easily removable flow restrIctors.

What is all the hot water needed for? A gas heater doesn't have to be in a well ventilated space because waste gases must be vented to the outdoors. It just needs source air and that's very easily done. Running a gas line is never a structural issue...it's a money issue. If two 50 gal units is a small fortune to operate...wouldn't one be 1/2 a small fortune? Still sound like a lot. I mean it's not like the second unit would cost 2x,4x,10x more than the first unit. That is kind of the deal if you want lots and lots of hot water on demand...it costs money. Solar can get you lots of pretty cheap hot water, at least DIY. The units you buy seem kind of expensive to me for what they are.