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

This post might be old but id like to respond. HI, Big Bias I'm seeing here... I would like to show some transparency so people know the actual costs. I would also like to note that i'm not including Markup to pay for things such as both types of insurance working and worker, Municipal licencing, Over head for a shop, Gas and insurance for a vehicle, the time it takes to order products as well as picking up/ delivering products. Expect a mark up of 26-37% on everything to pay for these items. If it's a Small one man company out of their home figure on the low end. If it's the largest plumbing company in the district expect to pay more. On the flip side they may get a bigger discount on the unit and hide that mark up in the unit it's self. My location is Alberta Canada, So keep in mind CND$$$. A typical 40-50Gallon Natural Draft hot water tank is 36-50k BTU's . A Rheem or Renai or Navian tankless is typically 140-205K BTU's . The Tankless will need a larger gas line. Usually needing permits. In my Jurisdiction The inspector gives a 4 hour window for inspection. So you'll be paying for a plumber for 4 hours. On top of that Tankless units DO NOT use the same venting as a Natural draft old style water tank. Thus a Venting inspection by the same inspector. Permit needed. So you will be changing two Major components of your homes "gas" and "venting" systems. Typical install time is about 4-6 hours. This includes, Turning off the water supply, Draining the house and tank, Unhooking the venting, Unhooking the old water supply. Then Mounting the new unit to a wall or Optional Metal rack carrier, Running new water supply lines complete with new valves and possibly a new Humidifier valve if the old one was above the hot water tank. Once the new lines are run, then they can Cap the old Vent. In some Jurisdictions this vent may be removed all together with a general contractor removing and capping the roof. Again more permits needed in this case. After the old venting is capped. then running new venting out of the side of the house. which has to be 12" from other venting or 3' from any opening door window or gas meter. If it's an older home you'll need to hire a Coring contractor to Core a hole through the Cement foundation. If the home uses TGI joists you can typically exit through there. Once the venting is complete the contractor can move on to the gas line. Cutting gas to the home for up to a couple hours Hopefully using "lock out tag out procedure" IE locking the riser while they work. They will open the outside of the gas line close to the meter Then Purge. Meaning to leave it open to air for 10 minutes. Some companies use a manual pump from the inside to push the gas outside. Once purged properly the contractor can start to take the gas line apart to add a tee. Remember he was supposed to "Size the gas line" at the time of Estimate to make sure your home has a large enough line for the added BTU's If he doesn't show the inspector this Calculation he could instantly fail inspection even if he did a good job. Most contractors will install a hard Tee then run Flex CSST Gas line or "Gas Tite" similar product. Once the gas is hooked up they do another purge the other direction. removing air from the line from the outside in. once gas is at the fixture it's time for commissioning. another 20 or so minutes till he's done. In my Jurisdiction the venting materials are to be Gas 636 PVC piping minimum. In multi unit dwellings it will need to be a higher spec. Cost of venting materials depends on length but the average is about $210 2" Double that for 3". Parts, correct type of glue Primer and glue. (the inspector checks), 2 45's 4 90's , 2 couplings, TY, 4 lengths of pipe. Seems rare to have an up and out easy unit. but costs obviously for that $60 or so depending on elbows needed. Gas permit $212.65 Materials gas $85.00 15' CSST, CSST adaptors, Nipples, Black 1 1/4 x 3/4 tee, Tape, jet lube, Materials Venting $210 4" B-vent Cap, 636 pvc piping & elbows Optional Rack $310 1/2" Plywood and screws $32.00 6 hours labour $510 Inspection time say we're lucky and only wait 2 hours $170 Owner supplied Tankless install 1219.65 Navian NPE-240A Wholesaler price $3044.22 Including Service kit. Some companies may get a higher discount through volume. Navian NPE-240A Amazon price 2800.00 No service kit https://www.amazon.ca/Navien-NPE-240A-Premium-Condensing-Tankless/dp/B00FAMAB2U/ref=pd_lpo_sbs_60_t_0?_encoding=UTF8&psc=1&refRID=P40Z2FYMVNSYE4DJ1A24 Also don't be fooled when it says 1/2" gas line the actual fitting is 3/4" it's just saying they have a special valve inside that allows for lower gas flow but in turn the burner does not run at full capacity. Total Canadian Dollars $4263.87 Transparent Fair pricing

I don't know what unit takes 3 -40a circuits or any costing several thousand dollars.Mine is rated at 120a, has two 60a breakers in the house subpanel, and two sets of four ganged 40a breakers in a separate subpanel for the unit. This is a single-family house, 3BR, 2 full baths, 2 half baths (one is in the garage). The house was built 4 years ago by a developer, I don't know what the tankless cost. I vaguely recall that sales literature I saw later for the unit involved indicated $1,025 retail. I've seen it run at full-capacity only during cold-snaps of near/below freezing temps that lasted a couple days which dropped the incoming water temp (well-water) pretty low, when I raised the set-point to 140°F for a specific hot-water task. Typically it runs as little as 7% of capacity to 66% or 70% ... but of course still needs a 120a circuit.

The point of a tankless water heater is to have a continuous supply of hot water that, unlike a standard water heater, will not run out. It can only provide instant hot water if the tank is at the point of use. There is nothing magic about it that will repeal the laws of thermodynamics and fluid flow. If there are many feet of piping that the heated water needs to run through, particularly if some of the run is in unheated space, there will be the type of lag you are describing. This is because the heated water has to displace whatever cool/cold water has been sitting in the pipe, and because that heated water will also will lose a lot of heat to the cool piping until that piping gets to be about the same temperature as the hot water. Only when the sitting water has cleared and the piping is heated up will you get water coming out at the temperature you want. This is not unique to tankless units...it's true of any type of water heating system where the heated water has to travel a bit before it gets to the point of use. If you want hot water faster, you'll need to move the tankless unit much closer to where you are using the water.