Free Heater Idea

[ejmyrow]

We will see if this works. Our landlord is an engineer. He is thinking of using a copper tube to pipe the hot water from the hot water heater (with a coil formation that will snake on the wall) into a room in the house. We have instant heat (that water is always quite hot) so we'll be using a resource that we already have to heat more rooms in the house for free.

[Louisville]

It's not free. The heat in the copper coil goes into your room. That means the net heat in the coil/water heater system is less, which means the water heater then turns on to get the water back up to the set temperature.
If your landlord is really an engineer, he knows this. A water heater for making hot water is not the same thing as a boiler for generating steam heat. There may be code issues with trying to do something like this. I'm not saying it's dangerous, or even inefficient, but it sounds kind of hinky to me.

[Smokystache]

I'm not engineer, but here are a few comments.

1) MMM did this to heat his house, but put the coils in the floor: http://www.mrmoneymustache.com/2014/02/16/the-radiant-heat-experiment/

2) If you think this is free, I have some bad news. As the heat transfers from the water, through the copper pipe, and warms the air - the water gets cold (or more precisely: loses its heat). So when it goes back to the hot water heater, it cools the average temperature of the water in the tank and the water heater needs to kick on to heat up the water again.

3) Unless you have a fan or some other method of moving the heated air throughout the room, I would expect that you wouldn't get distribution of the heated air. Sure, some will move around as the nature process of air trying to rise, etc., but it won't heat a regular sized room, unless you really have a lot of pipe and it is over quite an area.

4) My personal experience with this type of set up is that it's basically a heated towel rack - they're pretty popular in Europe:
https://www.cleanandtoasty.com/7-reasons-why-towel-warmers-are-so-popular-in-europe-3-will-surprise-you/. Great for heating your towel and slightly warming a really small bathroom, but not really feasible for heating a whole room .... and no one claims that it is free (doesn't use additional energy).

But it's always good to be thinking about alternative methods for energy use/conservation.

[terran]

Isn't this how baseboard heat and radiant floor heat (as smokystache pointed out) work, except that those systems have water heaters designed and sized for this purpose instead of being designed and sized to provide domestic hot water only?