In-ground spa design help/advice needed

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pwest

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Jan 13, 2013
5
Atlanta, GA
Hello:
I am planning to replace my backyard deck with a concrete and stone patio with an in-ground 8’x9’ gunite kidney shaped spa. I am working with a landscaper who has done a lot of excellent stonework and hardscaping for me in the past—he’ll be doing all the work except for the spa, which he plans to sub out to a PB (with no additional overhead or passthrough fee to me).

The spa specs from the PB are:
• 250 kbtu gas heater hayward h250fd
• 2 speed 1.5hp sp32152ee tri-star pump
• 1.5" s270t sand filter
• 6-anzen #7 jets
• goldline p-4 controler and salt system
• all 2" plumbing and drains
• one LED light
and he’s quoted a price of about $15,700.

First, does this equipment seem appropriate for this system? (The pump will be located 20’-30’ from the spa and around one corner.) Does the price seem reasonable? (Remember that the landscaper will be doing all the hardscaping and stonework out of his separate budget)

Second, I’ve been having trouble getting schematics for spa-only systems and have been wondering how these systems really should be plumbed. Clearly, there needs to be a high-flow ‘therapy’ mode for when the spa is being used, and a low flow filtration/SWCG mode that I presume needs to run maybe 4-8hrs/day. Is a two speed pump the best way to do this, or might two appropriately sized pumps be better? Is it standard to run the high-volume flow through the filter? Obviously that’s a good idea from a filtration standpoint, but not so good from a dynamic head standpoint. When in ‘filtration’ mode, does the pump draw from the same places and discharge into the same jets, or should there be a skimmer that comes into play?

Finally, I’m looking at both the filtration quality and head loss associated with the sand filter and thinking that the cartridge filter really looks better for my application. I know people usually reply with the ‘personal preference’ line on this, and I’d appreciate any comments that would help me make that decision.

Thanks for your help,
Phil
 
First, 2" plumbing for the spa is much too small. Spa's should be plumbed with a minimum of 2.5" plumbing unless the PB is planning multiple loops (i.e. separate 2" lines for each set of 3 jets).

Next, I always recommend a separate filter loop for the spa even though you only have a single pump. This can come in handy if you ever decide on a separate spa jet pump (see next).

Next, I would recommend a separate spa jet pump. Sending high flow rates through filters and heaters will only shorten their lives and weaken the spa jets. Not necessary but a better set up IMHO.

Next, the PS-4 only has four relays. If you want to control pool lights, garden lights, multi-speed pumps, and other things, I would recommend a PS-8 for the extra relays.

Next, S270T is too small if you plan on having a single pump. The head loss will be quite high and you will be exceeding the design flow rate by a lot. I would go with at least a 310. If you have separate jet pump, then this size is fine.

Next, 250k BTU will take much longer to heat the spa than a 400k. It will make a big difference if the water is cold.

Just a couple of items. :?
 
Welcome to TFP!!!

First, sorry this post is all over the place, as I am kind of thinking "out loud" ... Mark's post I think says the same thing ... maybe a little more organized (trust him more on the filter stuff) ;)

Not sure on price, but here are a few thoughts:
-Cheapest option would be to keep the single 2-speed pump and use low for filtering and high for jets.
-Generally best if when running the jets, you do not go through the filter (so you would need a bypass when in spa mode ... could be automated valve that diverts around the filter with a check valve on the filter output). Then you would run through the heater ... I suppose you could set it up to run either through the filter or the heater if you did not need heat when just filtering.
-Up sizing plumbing is always good. I would consider raising the return plumbing to at least 2.5" for better flow.

Contrary to what you said, the filters work better at lower flow rates. I would also say that a skimmer is a good idea.

The advantage of a 2 pump system would be to have a small pump to run through the filter and the heater and then a larger one to run the jets, but you then typically have 2 sets of drains and would need 2 sets of returns. So this will cost a bit more upfront and for electricity ... in fact, you may still want a 2-speed for the filter pump to allow you to run on low speed.

With just a ~1100 gallon spa, your filter size does not have to be big. For 5000 gallons we would recommend: 70 sqft cartridge or 1 sqft sand or 14 sqft DE. There is nothing wrong with a cartridge filter and many people prefer them. And you really can not go too big ... which will reduce the frequency of cleaning them.

One tricky bit would be the SWG. Likely you would only want that on while running in filtration mode so the levels do not get high if you use the spa for a long period. This would point to not wanting the SWG on the heater loop. Although, actually, some automation will turn off SWG while in spa mode I think.

Finally, generally for heaters, big is better. You will use the same amount of gas to raise and maintain the temp, but the larger heater will do it faster. This is good if you do not maintain it heated at all times and only want to raise it right before use. There are current discussions of spas taking up to an hour to get to temp in the winter ... so just depends on how long you want to wait.
 
Thanks for all this input! I had been reading these forums and doing some calculations and expected to hear that the 2" plumbing was too small. I talked to the PB today and he stuck to his original proposal--that 2" was fine and that there was no need to bypass the heater or filter when in jet mode. Of course, he's got no problem with using 2.5" plumbing if that's what I want, and he pointed out that it's relatively easy to reconfigure the plumbing at the filter/heater with a bypass valve anytime in the future.

Right now, I'm leaning toward upgrading to 2.5" plumbing and a 400Kbtu heater, changing to a cartridge filter and putting it and the SWCG on a diverter so that it's bypassed during high flow. The max flow for the heater is 125gpm, so it's probably OK to have it both circuits to maintain temp. This would seem like a good compromise between the original proposal and a full two loop dual pump system.

-Phil
 
pwest said:
The max flow for the heater is 125gpm
Click to expand...
True but it will cause a lot of head loss at that flow rate. The main reason for bypassing is to reduce the head loss so the jets remain strong. It saves the filter life too. If you don't bypass, then you might consider a larger pump that will cost more to both buy and run. Otherwise, you might be very disappointed with the jet strength.

Search the forum, there are many examples of poor spa performance due to small pipes, small filters and high head loss heaters. Their PBs told them the same thing.
 
It isn't necessary to bypass all of the water only some. Flow enough water through the filter and heater to keep the heater running (~30 GPM). Plus, I wouldn't send unfiltered water through a heater, that could end up clogging the heater with debris.
 
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