A neighbor of mine put up a above ground pool a few weeks ago and when I was preparing the site for him with my tractor I came up with the idea of putting 3/4" pex in a continuous loop on top of the soil prior to putting the sand down. He runs it off his wood burning outside boiler. When the pool was filled the water was 68 deg and he brought the temp up to 86 deg in 2 days. We were both really impressed. Works alot like radiant floor heat and the sand really holds the heat well and transfers it well. Anyone who has ever walked on the beach in Florida.
Chris
That would work, unfortunatly he is also pumping a lot of heat into the ground. Thermal transfer is always from warm to cold, and the earth below and around the pipes is always going to be cooler than the pool above. Foam sheets under the pipes would make it a lot more effective by lessening the path to the earth heat sink and forcing more heat toward the pool.
Insulation makes a big difference. We switched to a new above ground pool this year. We had one of the 12' quickset pools with the inflatable collar(big bag of water) and I have a sandy circle I prepared to set it up on. Well that pool had come collar issues that I couldn't resolve so we got a new pool with a frame. Didn't want to waste the prepped water in the old pool so I set the new one up right next to the old on an unimproved surface(grass). I was worried about the bottom, so I layed out some 1" thick white styrofoam sheets that I had in my barn(six 4' x 8' sheets). This pool is the same diameter and nearly twice as deep(2200 gallons). I have a 4'X10' poly solar collector I float on top of the pool to add some heat(pump pushes water thru small tubes). This is the same heater I used on the old pool to add heat during sunny days. I am also using a clear sheet of visqueen layed out on the waters surface to control evaporation, the same as I did on the old pool. I was very pleasantly surprised that this new pool has easilly been running 10-12F warmer than the old pool ever did. I kan't hardly keep the grandkids out of it as it is warm enough for them to stay a very long time. I think this is mainly due to the foam underneath. It also makes a real nice soft bottom...
In my opinion, the only cost effective way to heat a pool is with solar heat. I just got the material for an inexpensive solar experiment that will set on my roof. Well inexpensive because I already have the pump to be able to pump water that high. It will have about 120 SQ/FT of collector surface, so we will see if that will extend our pool season a little bit.
Wood heat will work, and that same 50# of wood over an 8 hour period would raise my pool temp more than a 5K gallon pool, but that is still a lot of wood and a lot of work to prep and keep it fired and heating properly. I think a wood fired hot tub would be a lot more practical
With good boiler efficiency, It would take about 18# of wood to get a 250 gallon hot tub from 40F to 100F A 50KBTU pellet fired boiler would do that in about 2.5 hours, and be fire and forget. Flip a switch when I get home from work, and it is ready to soak by the time dinner is done
