Water heater/manifold proximity
dfvellone
| Posted in General Questions on
I’ve got a bit of an obstacle that makes installing my home-run plumbing manifold close to the heater pretty tricky.
The only other alternative would have a 15’ run of supply from the heater to the manifold. Is this distance too long to even consider from a practical standpoint?
Thanks, Daniel
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Replies
No
I don't see a problem. The only potential downside would be slightly longer wait times for hot water, assuming you're running larger pipe (1", etc.) between the water heater and the manifold, and smaller runs (1/2", etc.) from the manifold out to individual fixtures. I wouldn't worry about that, just be sure to insulate the supply line between the water heater and the manifold to keep thermal losses under control.
Bill
I have pretty much this exact setup at a rental and hot water wait times are pretty long. That 15' of 3/4 pex holds about 0.3 gallons of water which doesn't seem like a lot. The problem is a typical 2 gpm faucet doesn't flow at very high velocity so instead of the pipe being emptied out as one big slug of cold water, it slowly mixes and warms up as you draw.
Hot water manifold should be close to the tank. Cold water manifold can be anywhere.
A single run off of the remote manifold could be used for a thermosyphon loop back to the hot water heater tank. That woud eliminate the delay getting hot water due to the run of pipe between the manifold and the water heater, at the expense of increased standby losses. There are always tradeoffs, unfortunately.
Bill
Deleted
Long timeframe between my original question and this follow-up, but I just put the system into service. The length of 3/4” tubing from the heater to the manifold ended up being 12’. Is the thermosyphon as simple as a return off of the manifold to the water heater drain valve? Thanks, Dan
You need to bring a line off the farthest point of the system that you want included as part of the "loop" that the thermosyphon will keep warm. That can be a small 1/2" or even 3/8" line, since it's a very low flow. You need to insulate the entire loop with pipe insulation.
The return line needs to go into the water heater drain valve at the bottom of the tank, and it needs to pass through a swing-type (NOT a spring type) check valve, allowing for flow in the direction FROM the thermosyphone loop and INTO the water heater drain. The reason you MUST use a swing type check valve here is that the convection flow of the thermosyphon isn't powerful enough to open a spring type check valve.
Note that with most modern water heaters, you also need to remove or otherwise disable the anti thermosyphon device (usually a simple plastic piece) inside the hot water output connection on the top of the water heater.
BTW, I'm not sure you'll really see much benefit from a thermosyphon, or any time of hot water recirc system, with a main run of only 12 feet in length. Usually hot water recirc systems are used when one or more fixtures needing hot water are located a significant distance way from the hot water heater resulting in long wait times for hot water. If you have a fixture like that coming off of your manifold, you'll want the return line tapped off as close to that distance fixture as you can get, NOT from the manifold itself, becaue you want to keep the water warm in the long run of pipe to the distant fixture -- it's that "keep the water warm in the long run of pipe" part that cuts down on the wait time to get hot water.
One last thing: I recommend putting a ball valve in the return line right where it taps off of the main line, and again near the water heater drain valve. This lets you isolate the recirculation system if you ever need to do any service work in the future, and keep in mind that the check valve may need to be replaced at some point.
Bill
Thanks very much for this detail. For the purpose of clarifying, I’m interested in the thermosyphon just for the purpose of creating a loop for the 3/4” hot water supply from the heater to the manifold, the length of which is 12’. The thermosyphon seems simple enough, but do you think that the loop won’t make much difference to make it worthwhile? The home runs are all 1/2”, and from a cold start it seems like that length would add some delay to my longer runs. Dan
The 12 foot run will add some delay, but I don't think very much -- maybe 10 seconds, if even that? You could calculate exactly how long it will take using the water volume contained in the 3/4" pipe, which is just over 1/4 gallon. If you know the flow rate for your fixtures, you can easily calculate how long it will take to clear that 1/4 gallon from the 3/4" run of pipe, and that is how much delay the 12 foot run is contributing to the system.
I wouldn't bother with a recirculating loop for such a short run myself. I think you'll be OK just being sure to carefully insulated all of the hot water lines.
Bill
Nope, ours is about the same. Just as a FYI, homerun + distance to mani = may take a bit longer to get hot water at the faucet.