Replies

1. 
   Guest_ | Sep 01, 1999 06:33am | #1

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   Kevin
   If you have an electric water tank forget circulating your water unless you get free electricity or have a BIG pocket book. I did this and my water heater ran constantly. I beleive you can circulate without a pump using gravity if your pipes are pitched correctly. My grandfather was a plumber and told me of this. You can get a 110V circulation pump though for about $100 or so. I tapped mine into the bottom of my water heater using the drain valve. I placed a nipple and tee in it to extend the valve and hook the pump up. Be sure to insulate your water piping. If im not mistaken you must return to the bottom of the tank. Also the return line needs to be smaller than the supply. I used 3/4 supply and 1/2 inch return. hope this helps

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   Guest_ | Sep 03, 1999 05:22pm | #2

   *Using the smallest supply that you need for the flow will help on long runs. (some times cheaper IS better)A very small well insulated electric tank or an instant heater in the hot line under the sink is also a good choice especially if small amounts of hot water are used most of the time. The thermostat should be set about 10 degrees below the main DHW heater. I have used this method in church bathrooms often, usually with the instant heater. When large amounts of hot water are used the thermostat in the small heater shuts off and the main heater is supplying the heat.

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   Guest_ | Sep 04, 1999 05:57am | #3

   *Kevin: I'm going to be a bit wordy here. This is a topic I've thought and played with a lot. I just plumbed a thermosiphon loop into my own house last week. Used 3/4" insulated copper for the loop and 1/2" for the laterals to each fixture. I put a brass-bodied swing check valve ($5 at HD) at a 45 degree angle in the return loop. I did that so it would hang open a bit for the thermosiphon which is a very low flow. You need the check valve because the return is tied into the cold feed of the hot water heater(HWH). Without a check valve the easiest path from the water main to some fixtures will be the return loop, not through the HWH (i.e. a mix of hot and cold water will come out the hot faucet). And it's got to be a swing check or a ball check, NOT a spring check. Spring checks come 1/2 or 2 psi which is way more than a thermospihon generates.While 1/2" pipe thoughout would reduce the transit time for hot water to get to the end of the line, you'd notice the pressure drop when multiple fixtures are used (i.e. cold shower when someone flushes).Regarding utility costs: I've got very cheap natural gas ($0.38/therm) and in Alaska 8 months of the year are heating season anyway. If pipe insulation averages R-2 and you've got a 50-foot loop, then it will lose 5,000 BTU per day = 1.5 kwh/day ($0.12) or 0.05 therm of natural gas/day ($0.02 for me). But during the heating season, it's free because you'd add that heat to the house anyway. For a pumped system, you typically put them on a timer (6 to 8 am and 6 to 10 pm) and so the heat loss is reduced 75% (6 hours instead of 24). But you have to add the electrical consumption of the smallest circulator pump you can find (Teel has 1/40 hp, but I think I remember seeing a 1/100 hp once). If 1/40 hp = 20 watts is used, you'll add 0.12 kwh a day (one cent) of electrical consumption. Worth doing to save $33/year on a electric HWH usage, but not worth the investiment if you've got natural gas. Pump will be about $100 as Brian says. If you can't find a timer for under $20, use a lamp timer ($6) like the ones to convince the burgulars you're home. In these calculations, I haven't figured the savings of hot water due to not have to purge the pipes of stagnent water. If you save 1 gallon of water 12 times a day, that's 7,000 BTU/day - a bigger savings than any of the losses described above. So overall, in any of these schemes you may well come out ahead energy-wise and certainly have the wonderful convenience/luxury of instant hot water at all your fixtures.Regarding Brian's thoughts on HWH connections: If you are going to do a thermospihon and don't have much vertical to play with (at least 4-6 feet), then you should tie into the bottom of the water heater as he did. If you're doing a 2-story house and extend the loop to the top of second story wall, you'll have about 10 feet of vertical above the HWH and can use the hot and cold connections on the top of the HWH. Using the lower lower drain valve connection would always give you more thermospihon effect. Very important, fundamental point: The HWH must be below the piping loop for this to work. If the HWH is in the basment, you're home free. If on the first floor, run the loop in the ceiling for first floor fixtures and up from there for the second floor. If in a one-story house: run the loop in the ceiling and take the return line back to the drain valve. While a constant upsloping feed line and a constantly downsloping return line may seem neccesary, they aren't. You need 1) a check valve and 2) to have the loop above the HWH. Beyond those critical points, a short loop is better than a long loop. Using two 45's to offset is better than two 90's. Diagonaling through the joists will be shorter than two perpendicular legs. Height is good. Height difference and temperature difference drive the whole thing. The more height you have, the less temperature difference there will be (e.g. a higher flow rate in the loop will maintain higher, more uniform temperatures). -David

2. 
   Ted_Temple | Sep 04, 1999 10:16am | #4

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   I recently plumbed my small 2 story house, locating the water heater in the basement. I returned one 1/2 inch line from my farthest 1st story fixture and one 1/2 inch line form my farthest 2nd story fixture down to the location of the water heater. The line running in the joist space between the 1st and 2nd floors was not insulated while the underfloor and basement portions were. Will this arrangement allow for a termosiphon loop? Thanks for any suggestions.

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   Kevin_H. | Sep 04, 1999 10:16am | #5

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   I have a chronic problem with (cold) hot water. The water has to run a long time to come up to temperature. I saw an excerpt in a plumbing book at the library suggesting a return loop from the most distant hot water destination to the hot water heater thru a check valve. There weren't any details on sizing or distance for how this might be applied? Any experience or suggestions?