 | Tankless Water Heater (and Hot Tub Conversion?) |
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Question: We are looking into replacing out electric water heater with a tankless gas model and it occurs to me that there is no reason we shouldn't be able to also have it serve the electric hot tub also with a heat exchanger of course to keep the spa water out of the domestic supply. We keep the hot tub hot all the time which is normal for the electric "portable" spas. The guy at the hot tub company says "no way" but I don't see why. He said the constant low flow demand is just inefficient with gas but it still doesn't make sense to me. The tankless on-demand heaters are suitable for radiant heating and other low flow tasks. Just need a thermostat to give little 30 second boosts to the tub as needed. Maybe there is an inefficiency with starting that up and running the water through the long distance of pipe from the house to the garden (about 50 feet). Also, for the tankless water heaters, does anyone have advice for the brand and model to use? We are just two people with pretty low requirements. The stubby short electric heater now never runs out, it's just a matter of reducing monthly expenses. The Bosch Aquastar 125B website is about $200 less expensive and doesn't require an electrical hookup but the flow rate is only 3.6 GPM at a 50 degree temperature rise (other models are twice that). We wouldn't mind turning the dishwasher off when showering but don't want a cold blast if someone does a bit of hand washing in the sink while showering. Also for the location, I'm thinking it would really be nice to have the new heater closer to where it's used. The current delay bugs me and probably wastes energy too.
Answer: Well, I'll just ramble on with myself as I have more thoughts & questions... Another question is the venting. These things require a 5" vent and a couple plumbers suggested just hooking onto the furnace vent which is 5" but I'm not sure that's wise. It would have to go level for about 12 feet then tee into the vent right where it exits the building. Some models talk about additional power venting and some are recommended for wall versus roof venting. I guess that to wall vent a roof type model, I'd need to get an extra power vent thing? ...or it's not possible? I just met with the gas company repairman and he answered my questions below (after I wrote it all out) He said it's not a problem, I don't need to add a line back to the meter. Read on if you are curious but it's already answered. Worst case is that when everything is on, the heater might not work efficiently but it's not dangerous. Also there is the question of the gas supply line. The Aquastar uses only 117,000 btu's but the other models use about 180,000 btu's which apparently requires a dedicated 3/4" gas line from the meter. One guy said any of the computerized Japanese models will shut off if the gas supply is inadequate but the Aquastar is European and has no electric power so does that mean it will be dangerous without a dedicated supply line? I heard something somewhere about safety risks with inadequate gas supply. I don't want that but I don't mind if it's just poor performance on the rare occasion that we are baking, showering and heating at the same time. We rarely run the furnace. The current demand includes a big old fashioned gas stove, a new clothesdryer & a fairly big 30 year old furnace on a 3/4" pipe. The water heater would take off of that pipe where the furnace tees off. It's another 15 feet from that point to the gas meter and a total of 30 feet from meter to the water heater. The stove and dryer are another 20 feet away.
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