yeshwant91, A bit off topic but related... I'm not familar with all the combi units your considering, but consider carefully if those units will meet your needs. Some of the combi boilers I'm aware of have significant limitations. For example, in their instant hot water production mode if you exceed their max flow spec they will allow the additional flow and just start lowering the temperature of the heated water. In reality this may mean certain units are only good for a single point of use at any given time. So you might not be able to take a shower and wash your clothes at the same time. A couple years ago I was considering a Rinnai whole house instant DHW heater. They are very powerful units and have flow limiters so requested hot water temperature is always achieved. If you ask for more hot water than it can produce they will just ignore the demand for additional flow. Not sure which (if any) combi units also incorporate this feature. I agree with dross - if you can swing a 220V line do it for the sake of a much wider choice of washing machines with proven track records. I believe Miele/Asko/Bosch all use 220V-15A circuits for their washers. I understand you won't need it for the dryer.

You can probably go without the power vent and put in a heater that's the same as the original gas, basically a "b-vent." They are less efficient, BUT they will operate during a blackout, a power vent model won't unless you have a backup generator or large UPS to run it. You might want to get a "blower door test" done or try this experiment: turn on all the bathroom fans, kitchen exhaust fan if it vents outside etc, then turn up the hw heater and put a candle right next to the flue hat (the upside down funnel that runs into the b-vent) and make sure the candle flame is drawn towards the vent, so you know the flue is venting correctly - you don't want to draw combustion products back into the house. With two gas HW heaters you might run a bigger risk, so you might consider running a "make-up air vent" in, it's a pipe that runs to the outside and down to the floor of the mechanical room. The furnace and HW heaters draw in the cold air for their combustion. Having said all that, you may really only need one hw tank perhaps? That'd be a saving. If any hot pipes are exposed, insulate them, but the pipes (both hot and cold) right at the heater need insulating too, but a non-combustible insulation like fibreglass where it runs close (As for the price, when I replaced my hw heater, added expansion tank and re-worked some of my plumbing, I spent almost CDN$700 with a $400-odd hw tank, but I had to change a few things and add an expansion tank. Meantime I guess you could switch off the electric tank, and put a hw heater blanket on it to minimise loss.

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

As I type this my 14 year old tanked water heater is being replaced with a Navien 240. My warranty is 15 years on heat exchanger, 5 years on parts and 1 year free labor. No requirement for an annual service. Additionally, the company installing the Navien has a policy that guarantees if, during the first year I have the Navien, I'm unhappy with it, they'll remove it, and fully refund my money. They said they've never had a customer claim that benefit. All of their customers are happy. Last year, when the state tax credit was in effect, they were installing 2-3 Navien units each week. Install rates have fallen off a bit since the state tax credit has been dropped. Interestingly, they're installing Naviens only in existing homes. They were also candid that, like other new technologies, there were some hiccups a few years ago that needed to be worked out. In their opinion, all problems have been resolved, and today the best, most reliable tankless units on the market are Navien and Eternal. I chose the Navien because the heat exchanger is stainless steel, not copper, eliminating the need for the periodic de-scaling required of other makes. And because it appears easy to operate...more so than the Eternal. I'm nervous at the change. And I'll post back here after I've lived with the Navien for a month. I've got house guests coming later this month, and it'll be interesting to see how it performs with lots of showers, laundry, dish drawer use, etc. I'm so pleased to hear that Rob is delighted with his new Navien.