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Thread: Adding a second heater

  1. Back To Top    #1

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    Adding a second heater

    After having a heat pump for 3 seasons in massachusetts, I've come to the conclusion (actually mostly my wife's conclusion ) that I need a gas heater as well. The heat pump works great late May thru the end of August. However, early spring and September/mid October, it just does not cut it. So, this spring I'm going to add a LP heater and need sme feedback from some of you construction guru's on the best way to plumb this up. As an aside, I plan NOT to use the heat pump when I use the LP. IOW, when the LP is on, the heat pump will be shut off, and vise versa.
    Below are 2 different ways I have thought of to plumb two heaters together. The first 2 diagrams use one 3 way and one check valve (I've actully seen this before when solar is used in conjunction with a heater. The second 2 diagrams use two 3 ways and bypasses one heater all together. Keep in mind the heat pump will be off when the LP is running.

    What say ye?





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    Mod Squad Bama Rambler's Avatar
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    Re: Adding a second heater

    I prefer the second setup to the first in that 1) You're not losing head by running through the heaters in series and 2) You totally isolate the heater not being used so in theory it could be serviced while the other heater is running if needed.
    Dave J. TFP Moderator
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    Re: Adding a second heater

    Yea, I thought about the head loss too. But, what you cant see here is how I would have to actually move things around if i did it the second way. I have a SWCG that will have to be moved and re-piped in a different way. The runs will have to be longer since i have NO room to spare the way it's plumbed now (it's really tight). I would have some really tight turns and at least 2 extra 90's to contend with before I went back to the pipe that feeds the returns. I think i would have the same loss by doing it the second way as compared to the first. It might be a wash on that front, I'm not sure.
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    Mod Squad Bama Rambler's Avatar
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    Re: Adding a second heater

    Bummer when the real world gets in your way when trying to do things. I don't see a problem with the first, it's just the second would be my choice if I didn't have to add a bunch of plumbing and mkoving to get there.

    I say go with whichever way works best for your situation.
    Dave J. TFP Moderator
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    Re: Adding a second heater

    Yea, things look better on paper sometimes! I prefer the second too, but the 1st is easier by far. The head loss would not be an issue when the heat pump is running since its really the same set up as now. I'm no engineer so I wouldnt have the slightest idea what the loss would be or even if it wolud be significant. I know that the series plumbing is the way i have seen suggested for a solar set up with a gas heater or heat pump in series.
    14,000 gallon IG, Vinyl. Hayward 3/4 hp superpump, Penatair IC40 SWCG, Pentair automation, Hayward sand filter, Aqua Comfort heat pump, Hayward 400k Lo-Nox LP heater.

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    Re: Adding a second heater

    Head aside, since I didn't figure that in anyway

    I'd prefer to see valves to control the flow and isolate the 2 heaters. It's nothing I can 'put my finger on' but, I like to be able to control or fully kill lines that might not always be in use.

    Any chance of a pic (or direct us to some previously posted pics)? [as you well know, there are some really good folks here who might be able to come up with a 'work around' that hasn't occurred to you ]
    Luv& Luk
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    Re: Adding a second heater

    I could do the second setup, it would just take another half day and a few more swear words. I'm not so hung up on shut off valves for everything, really. Maybe i'm missing something but I dont see the advantage. If you need to work on something, you really need to shut everything down anyway. The only thing thats not isolated is the heat pump in senerio #1 when the LP heater is being used.
    I dunno, I'm still undecided. But I'm leaning to #1 since its easier and cleaner in terms of asthetics.
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    Re: Adding a second heater

    The only thing I can add to this thread is to make sure that, if you're isolating one of the heaters, you are able to completely drain the one not being used if it's going to be left this way for more than a day or two. This is more important with the gas heater, due to the composition of the heat exchanger, but standing water will become corrosive.
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    Re: Adding a second heater

    Something to think about. Although with set up #1, only the LP heater would have any standing water in it. The heat pump would always have water circulating under scenerio #1.

    Any advice on an easy way to drain without unhooking pipes, etc. ? It would seem to be not too practicle.
    14,000 gallon IG, Vinyl. Hayward 3/4 hp superpump, Penatair IC40 SWCG, Pentair automation, Hayward sand filter, Aqua Comfort heat pump, Hayward 400k Lo-Nox LP heater.

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    Re: Adding a second heater

    The heaters do incorporporate a drain valve, usually on the front header where the water pipes connect, but it usually will not completely drain the tubes unless you "tilt" the heater some to force the low point at the drain plug. I don't know any good way to do that other than disconnecting the unions.
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    Re: Adding a second heater

    I appreciate what Ranger is saying

    However, since you are a tried and true member of this forum, I doubt that you'd have to drain the heater in it's off time! The reason for draining is to prevent acidic water from eating the heat exchanger or overly hard water from depositing calcium on the exchanger, but - you don't have acidic or harsh water anyway, because you follow the advice here


    (**as recently as this year, I'd have said the EXACT same thing as Ranger - but a few posts have reminded me that the folks who come here, and care for their pools in the way advocated on this site, don't have to worry about that water still in the heater **)
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    Having done construction and service for 4 pool companies in 4 states starting in 1988, what I know about pools could fill a couple of books - what I don't know could fill a couple of libraries :-D

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    Re: Adding a second heater

    Thats what i was thinking Ted

    My water is soft and i only keep ~50 ppm calcium in the water. pH stays around 7.4-7.6.
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    Re: Adding a second heater

    Okay, maybe I'm missing something... Using the TFP method, how long can water sit idle in copper tubes and still be balanced? Generally speaking, I wouldn't want to leave it sitting for more than a few days, regardless of the method of maintenance. If the heater won't be bypassed for more than a few days, no problem. However, if water will be sitting inside the heat exchanger for a couple of weeks or up to 30/60 days, I don't understand what will prevent the water balance from changing as it would normally do.
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    Re: Adding a second heater

    How would it change sitting in a pipe?
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    Re: Adding a second heater

    ??... Exposure to air, metals, sealing compounds, etc., will naturally degrade the quality of the water. Many homeowners who maintain their water very well find pinholes in the copper heat exchanger from water sitting for several months thru the winter. Not usually the first winter, but over time, the balance of the water inside the copper tubes does change and should be drained. Perhaps we should agree to disagree on this, but even if there are questions, it seems better to take the small steps to drain, rather than dropping $500-$1000.00 on a new exchanger every few years.
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    Re: Adding a second heater

    I hear what your saying, and if it were straightforward to do, I'd do it. But honestly, i'm not too concerned. If I want to flush some water thru it, i'll throw a valve and flush it for an hour or 2 and then go back to the heat pump.
    14,000 gallon IG, Vinyl. Hayward 3/4 hp superpump, Penatair IC40 SWCG, Pentair automation, Hayward sand filter, Aqua Comfort heat pump, Hayward 400k Lo-Nox LP heater.

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    Re: Adding a second heater

    Quote Originally Posted by bk406
    I hear what your saying, and if it were straightforward to do, I'd do it. But honestly, i'm not too concerned. If I want to flush some water thru it, i'll throw a valve and flush it for an hour or 2 and then go back to the heat pump.
    Ranger is right on. Id just drain any standing water from heatexchanger when heater is not in use. Most of my customers dont want to even attempt draining the heater so like you said.. i have them open the bypass every couple days or so to flush new water into exchanger.
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    Re: Adding a second heater

    Quote Originally Posted by Heckpools

    .. i have them open the bypass every couple days or so to flush new water into exchanger.
    Not to belabor the point much more, but why wouldnt this work just as well? Seems like just draining the heat exchanger would not do much good. The only way to get all of the standing water out would be to blow the heater out as if you were winterizing it. Any water left standing in the heat exchnger, even a small amount, would cause problems (which i kind of dont agree with really).

    This brings up a larger issue as well. I hear pool guy after pool guy say to isloate the heater so water is not running through it when not in use. But, if you do that, according to you guys, the heater can be damaged. So its damaged if you run water thru it, and its damaged if you left water sit.
    I hear everything you guys are saying. I'm not busting on you guys, really, just pointing out a few little inconsistencys.
    14,000 gallon IG, Vinyl. Hayward 3/4 hp superpump, Penatair IC40 SWCG, Pentair automation, Hayward sand filter, Aqua Comfort heat pump, Hayward 400k Lo-Nox LP heater.

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    Re: Adding a second heater

    Chiming in a bit later here but your diag1 and 2 look OK to me, but I would tie them in parallel so if you want you can run both together at start up and later in the fall.

    I would add shut off valves so you could isolate 1 or the other to work on them and also an easy way to winterize.

    Also being in CT im having a similar problem with agressive heat using an outdoor wood boiler and a single heat exchanger. I most likely will be adding a second one in parallel so the fist one takes the shock of the coldest water then the second can really transfer the heat.

    Again since the HP is cheap to operate why not use both-- the heat pump to (pre heat) the water and the LP to really heat. This will save fuel costs and should give you greater heat output at a lower cost.

    Say your water in the spring is 55% the HP could bring the water to 65-70 then the 70% water could be heated by the LP. There is a curve to the amount of energy required and from 55-75 is much greater than 75-105
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    Re: Adding a second heater

    Actually, running both would be a waste of money. I've had the heat pump for 3 seasons and it really doesnt do much in September and October except make the electric meter spin really, really fast!

    Seriously, once the day time temps go down into the 60's pretty consistently, you can get much heat out of them. In New England, as you know, the days start getting short and warm ambient air for the HP to draw on goes down precipitously. Once the nights hit the low 50's, it doesnt warm the air up enough during the day to do any good. The best you can get out of one in the fall is around 80 degree water, which is fine for July, not so much for mid to late September. And even then, you have to run it at least 12 hours a day to keep it at 80. The next morning, its down to 76 or so, then takes all day to hit 80 again. And thats with a solar blanket. If it's raining, forget even that. In September and October, we use the pool maybe once during the week and on a weekend if the air temps are in the 60's. By then, we want 86-88 degree water, and you are not gettng that with a heat pump. To keep the water at 80 degrees, you have to run it 12 hours a day, 7 days a week. That runs about >$150 for 4 weeks of that. I can heat my pool 15 degrees with about $35 worth of propane. I can do that 4-5 times for the same amount if electricity runinnig the HP constantly and only hitting 80 degree water temps.

    In the spring, the HP works a little better, but I can use a little LP and get the water up to 86 pretty fast. HP is REALLY slow too. Where a HP really shines is late May-early Sept. Cool New england nights make heat a must, but the daytime temps in the late spring and summer make a HP more economical to keep the pool at 82-83 24/7. If you tried that with LP, it would cost a lot of money.
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