Our home was built around 1963 and has Gas powered Hot water based heating, some portion of the house is floor heated and some with radiators emitting heat from hot water. The heater may be 10-12 years old. This is Lochinvar heater. Our inspector said this may be at its end of the life. Our house has central air conditioner and air conditioner handler is in attic up above the bedrooms.

This our third winter with this heater and broke three time already and spent ~800 USD for parts and labor.

Here are my questions,

  1. Our system doesn't have mixing valve to cool down the water to certain level before it goes into the concrete floors. How dangerous/expensive this would be if this breaks?
  2. If missing mixing valve is a problem and since I already spent ~800 USD for maintanance, should I wait for the boiler to die or should I proactively replace it with new one?
  3. If I am going to replace it, are there any advantages to going air based heating? Is it feasible since our air conditioner handler is already in the attic? or should I stick with water based heating?

Thank you!

I understand, I am asking a lot of questions in one question, I am just afraid, breaking it up in smaller questions might not give the full picture.

2 Answers 2


Hot water heat is the best heating system out there. Forced air, by its nature dries out the air as it passes through the unit, unless you have a humidifier as part of the system. The temp of the water gong through the pipes is not controlled by mixer. I don't know the temp it is supposed to be when it leaves the boiler, but when it goes through the lines and returns to the boiler it still has to be warm enough to be reheated to the same temperature as before. If it doesn't, the heat being dispersed by the pipes will loose heat gradually and the circulator pumps or the boiler will never have a break, they will run continuously, or at least more than what they need to. What I am trying to say, is a well engineered system does not need a thermostat on the water temp, just a thermostat in the room to tell the circulator pumps and boiler when to fire up.

If you are concerned about the pipes in the floor, not knowing what the material is, makes it hard to determine how long of lifespan it may have. Usually, anything buried, not exposed to environmental conditions, sunlight and such will last quite a long time. Presumably the material in the floor is not affected by direct contact to concrete either. The place where the pipes come out of the floor is where the biggest concern would be if any. Again, I have no idea what was used for the pipes or what may have been used in the 60's for this type of application.

  • Mixing valves are actually common on systems with a combination of radiant heat, baseboard or radiators. They all run optimally at different temperatures. It diverts some water that would normally go into boiler back in the the loop for floor heat or radiators lowering the temperature. Baseboard are normally at 160-180 degrees which is way too hot for radiators or in floor heat.
    – Justin K
    Commented Mar 17, 2014 at 2:52
  • This is news to me...I have overseen install of in slab radiant heat, and have never seen a mixer involved. 4" of concrete mellows out the high temps, or so I would think. This is for heating, not just for tempering, even that has not had a mixer in use. I guess I have not seen it all...
    – Jack
    Commented Mar 17, 2014 at 3:27
  • "Forced air, by its nature dries out the air" It is a commonly held belief that forced air heat dries out the air more than radiant heat, but it is actually a myth. See: bookstore.ashrae.biz/journal/download.php?file=ASHRAE-D-AJ11MarHVAC-20110305.pdf Commented Dec 8, 2015 at 22:48

In slab water temp should be around 100 degrees but that is just for efficiency. So if it has been running for 50 Years without one I am sure you are fine. As long as there is no leaks in slab heating I would stick with it. In floor heating is becoming popular again. It is much more consistent quiet heat.

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