I am in the process of getting my boiler and hot water heater replaced. One company gave me a quote for a Weil McLain boiler and indirect hot water heater. Another company gave me a quote for a bosh boiler with a tankless hot water heater built in. There is 3 of us in the house and we wash dishes and do laundry while others take a shower.

Can anyone give me the pros and cons and which setup is better. Everything I read, tankless has maintenance cost and is cheaper to install, but every article I read leans toward indirect.

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    What's your climate zone? Country? Style of heating (e.g. single pipe steam, air to air heat exchanger)? – Bryce Oct 24 '14 at 16:14
  • The climate zone is zone 5 and 4 marine. I live in the United States. As for the style of heating I do not know. I have baseboard heat with a boiler. – MOE12 Oct 24 '14 at 16:53
  • What do you currently have? What issues caused by the current system do you expect the new system to solve? – ben rudgers Oct 24 '14 at 19:00
  • I currently have a weil mclain boiler and a standalone 40 gal hot water heater. I currently do not have any issues with my system, but considering it is 52 years old I think it is time to go more efficient. – MOE12 Oct 24 '14 at 19:32

Tankless units are limited in the amount of hot water they can produce. It is rated at a certain number of gallons per minute. Think of it in terms of continuous versus multiple use. With a tankless unit rated at 7 gallons per minute you could shower with a 3 gallon per minute shower head until you ran out of fuel. If three people were multiple showering at the same time your use would use 9 gallons per minute and you would run out of hot water. The plus of tankless is you only heat water when needed. However if the tankless unit is part of your furnace it will cycle to maintain a minimum water temperature. With an indirect unit the water in the furnace will heat tank water via a coil in the storage tank. The furnace will still cycle to maintain the internal temperature. You are keeping approx. 40 gallons of water hot for when you need it. The key to an efficient indirect heater is a well insulated tank so the furnace doesn't have to run very often to heat the stored water. This is usually specified as degree drop per hour. Your decision needs to be based on a calculated maximum hot water use per minute versus the capacity of the tankless. Then compare the added cost and how long it will take to recoup the cost based on utility prices.

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