(Copper, PEX and discount van hire cpvc are relatively cheap compared to Stainless Steel vent piping!) This also may give you a reason to get some needed space back within the home.
Even the big tank water heater companies have tried to jump on board by partnering with larger Japanese companies to have units private labeled for them (More on this barclaycard carnival rewards later) Tankless water heaters are available in electric natural gas and propane fired models.
The third cause is lack of flow. One manufacturere has a built in buffer tank to eliminate this entirely (Navien) if it is a concern to you.The popular soaking tubs hold anywhere from 45 gallons to over 80 and just filling up the tub leaves most without any hot water with a tank type heater for a period of time. Manufactureres have come up with ways to control the systems so they can do both jobs very well and many engineering firms are specifying them in large appartment and condo projects.For instance, a RA32 in central Virginia can be expected to handle.5 baths. .There are very few homes that need more hot water than a twin tankless system can produce.Sometimes if only a small zone is operating, the Mod/Con may cycle off until the water temperature in the primary loop cools enough to require it to operate.Many, like the Rinnai even come with "outdoor reset" which allows the boiler to change it's output temperature based on how cold it is outside! .A Mod/Con heating a space under a reduced load will operate at a lower firing butterfly thank you gifts rate and save fuel. .Now this first quart of water enters the pipe with the water that is still hot from the last draw and begins to mix with it as it travels down the line.Even when you are using hot water with a tank heater there is very little movement of the water.Navien is comming out with a wireless remote to allow for easy locating of the remote in retrofit instalations.The condensing gasses would quickly begin to cause damage to the masonry and result in structural damage to the property as well as a very unsafe condition with carbon monoxide.This has kept most builders from using them in new construction.
For instance, a home needs 87,000BTUs of heat under design day conditions.