Bosch tankless heaters suck.The heat exchanger froze 2 months after it was installed.Bosch replaced the first one and suggested putting a small fan on the floor to blow warm air up through the exchanger.This did not work.I have had this water heater 4 years and have been through 3 heat exchangers.Their 10 year warranty does not cover freezing.They sent me information about their heaters freezing that was dated 2002.They have known about this issue for at least 6 years and they have done nothing to fix it.I first asked if they had any newer style of exchangers that were not prone to freezing.They said no.I then asked if I could exchange the whole unit for a model that would not freeze up.They said no.I have offered to ship it back to them at my expense for a refund but they will not do anything about it.They insist that I should have to modify my homes ventilation to accommodate their heater rather than them make design changes to their flawed product. I explained that Ive already spent $500 on the heater which is $200 more than a tank heater.Now they say I should spend more money on a HAVC specialist to modify my home!Any savings that could have been gained has been lost due to the freezing issues.There is no warning on the box about using the heater in cold weather or with a fireplace in the house.They did send a bulletin after the first freeze-up called "preventing a freeze-up from negative air during cold weather".It gives a list of requirements about venting and the amount of open space for combustion which I have complied with.Heres what it says next:"When these requirements are followed,the unit will operate properly and safely.However,there still may be a risk of freezing the copper heat exchanger or the brass water valve from negative air if other combustion type appliances in the area are not being supplied with a sufficient amount of combustion air for themselves" they go on to say:"More make up air is the solution.It will be necessary to make other per...