Heating Hot Tub using household hot water.

I have a hot tub that is currently heated by pumping hot water from the house gas water heater through a copper pipe installed under the seats of the tub. I have been told that this does not meet code, because of the risk of a leak allowing "dirty" water to be sucked back into the city water system if the city water is shut down for some reason.
If someone out there is familiar with the code requirements for such a system, I would appreciate consideration of the following questions.
1. Is my current system in violation of generally used plumbing codes?
2. Would any of the following make it compliant?
a. Installing a check valve on the water heater input to prevent backdrawing of water. (With associated expansion tank) b. Installing a check valve on the house water input line. c. Adding a simple counterflow heat exchanger. I see this as a 20' section of 1" copper turing with 20' of 1/2 inch copper tubing inside it. This would be coiled above the water heater, with 7-8' of it straight down along the heater. The bottom end of the 1/2 in tibing would go into the water heater drain hole, and the top end would connect to the hot water out from the heater. I am hoping that convection would produce enough water motion, so that an additional pump would not be needed. The current pump would pump water from a closed system through the 1|" outer pipe and the loop through the tub, going up through the added heat exchanger.
Any other ideas greatfully accepted.
In Seattle.
Bob
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

risk
out
Custom made tub?
Pumping the water into the tub? Never heard of such an animal. Where exactly does the water enter the tub? above or below the user water level. If below, then a check/one way valve should work.
Heat exchanger is just going to complicate the system. IMO
Best ask a local plumber or an inspector. Fix it right now so when you sell the place you will not be forced to fix it then.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
I believe that you need a double wall heat exchanger. In between the two surfaces is a rifled space that is vented. We used to use those when installing solar water heating systems with glyclo to prevent freezing. I don't know where to get one now.
Stretch
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Ahh! That helps a lot in the search engine. Thanks.
Bob
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

A backflow preventer might be simpler. As found in washing machines.
You might replace tub water with cold fresh water using a slow counterflow heat exchanger. It could be very efficient, at less than 0.1 gpm. How many gallons of fresh water per person-hour of use, to avoid using any chemicals?
Nick
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

chemicals?
You've lost me here Nick. The problem is, if the tube in the tub leaked (it carries water from the water heater), at the same time as a water supply failure, then tub water could be siphoned into the house water supply and therefore, the city water. Obviously, a leak in my current in-the-tub heat exchanger would result in quickly detected overflow of the tub, so the simultaneous failures are unlikely. But that apparently doesn't meet code.
I did some research at the library today. The wording in the code doesn't make it clear whether my counterflow heat exchanger idea might work. A double wall heat exchanger clearly would. Tomorrow, I'll research where I can actually get one, and what the cost might be.
Bob
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

of
it.
down
Yes
exactly
below,
Water enters below the water line. It is contained within copper tubing. No contact between tub water and domestic hot water normally occurs.

Definately. But i'd like to be able to re-plumb my house to code. I don't really want to add a separate heating device for the tub.

sell
That's the goal.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

And back to the water heater... Interesting.

Probably true. The GFX people say the worst-case scenario is a fire truck that hooks up to a hydrant and pulls a vacuum in the entire neighborhood.

These would add a little safety, if not compliance. There's also a more expensive thing ("zone pressure reduction valve"?) that not only prevents backflow if water pressure fails, but drains the pipes as well.

Sounds complicated.

This sounds safe enough to me, altho a pinhole might not be quickly detected.

You might follow reason, vs the code :-)
Nick
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.