Renovations - Pipe freeze protection?

[Auckie]

Soon getting vintage mobile home. Need replace plumbing.Will be using pex. Previous owner installed pipes UP, above the ceiling!!. (Ceilings are perfect, no sign of any problems ever- cold, northeast-) I guess the logic is that all the heat is rising but imagine the damage if they ruptured!! They are above the MH under a peaked metal roof under @18" of insulation.
It's all working great but will be adding dishwasher, moving washer to kitchen,new fridge has ice-maker, and anticipate building addition w/new bathroom- not enough water getting to that end- need more supply.
A few questions: What about the above ceiling thing? (The pex will be much more freeze tolerant than the plastic now there) A friend has suggested running them INSIDE of the heating duct in the floor instead, that way they are warm?? Crazy?
Lastly, I've been thinking about making the hot water run into a loop and recirculate it on a timer or thermostat. If I took both the hot, hot return & cold and wrapped them all properly with insul, I think the hot water flowing thru could easily work better than a heat tape? (At least it shouldn't need replacing every couple years.) Added bonus is hot water pretty quick to the faucets.
The plan is to install a new gas instant hot tank-less heater. There IS a brand new electric heater, but it's only 30 gallons and just too small. I plan to use the existing temp control on the current heater to turn on a circulator to pump water from the small heater thru the gas unit and back to the small tank. (Yes, some don't see the wisdom of introducing a tank to a tank-less system, but eventually I may use the system for heating also,and for that it will be a benefit. Many say the life of a tank-less unit is greatly extended because it is heating tempered water rather than cold ( The shock of the cold water being introduced happens in the small tank heater)and it will also allow me to size the tank-less a little smaller than the full demand would require as there are 30 gallons of reserve to begin with). So what say you all?? Pipes above or pipes below? In the duct? Hot water loop? or just use tape?-Auckie

[Greg]

Hi & welcome. you have posed 2 Ideas that I have never heard of, First pipes in the ceiling? I guess it would work, but the pipes were originally run NEXT to the heat ducts. The idea being that they stay warm from the heat near the ducts. I would go with the PEX and back to original location.
Now, Looping the hot water? I would think that could lead to some outrageous utility bills with the water heater running that much, but I guess it is possible. Greg

[Archie]

Much to think about here. If the belly of the home is in good shape or has been replaced I am not sure I would take the chance on destroying it to run new water lines if the old location seems to work. To me running the lines just above the ceiling, while risky if there ever is a leak, is pretty much the same as running the lines within the home along an outer wall but with much more insulation.

Pex is the preferred water line to use. It can expand many times it's size without bursting if it freezes. Speaking of freezing, I am not sure that many folks realize this but it does seem that hot water freezes faster than cold (under certain situations). Sure there is scientific reasoning for this but suffice it to say that the utilization of hot water in lieu of a heat tape would be a bad idea. Even if the water was to be recirculated by a pump it may not move quickly enough to prevent freezing.

They do in fact sell recirculators that work with a water heater. They are to be installed under a sink the farthest from the heater and recirculate the hot water so that it takes less time for it to reach that spot, helps to save water and possibly a little energy since the water may not be as cool going back to the heater as fresh water from the ground is.

As for a tank-less water heater. I am not sure but I think finding a gas unit that is mobile home approved will be difficult. Not using a mobile home approved water heater could void your insurance. They are also still very expensive at near a grand, you could install a larger electric tank unit that would likely last just as long for a third the price. You could also donate or sell the smaller unit to a neighbor or other needy person who might need a water heater.

Just some of my thoughts on this.

[Greg]

You are right about the hot water freezing first.
If I remember my high school science it seems like once the water starts to cool it actually accelerates once it starts dropping. since there is more of a drop on the hot side it does reach the freezing point first. I'm wrong I'm sure someone will be along to correct me. Greg

[StillKavey]

I always use hot water in the ice trays because it freezes faster.. my grandma taught me that.