pump size

[maplewoodshelby]

Not much expertise here locally on running dhw coil from boiler to water heater.
I'm planning on running pex which will be about 100 feet roundtrip from the boiler to the water heater.
Three questions: Should I go with 3/4 pex or 1/2 pex for this run?
What size pump should I use? It will be a pretty much flat run all the way to my 62 gallon water heater.
Ive been told by the boiler manufacture to run the pump 24/7 to reduce wear on the pump and ensure consistent hot water. Any thoughts?

 

[DaveBP]

Ive been told by the boiler manufacture to run the pump 24/7 to reduce wear on the pump

Huh?

 

[Duetech]

My only thoughts about running the pump 24-7 is thermal control if the boiler goes down for any reason and loses heat. Arbitrarily if your selected water tank mean temp is 160 and the boiler goes out and drops to 150 you should have a controller to stop the pump from sucking out the heat from you dhw tank. To prevent thermal siphoning in case of a shut down use a check valve. I have a sidearm heat exchanger on my dhw tank which is convectional and the motion of convection is no where near the turbulence common with pumped water. If you were concerned about stratification I would suggest the largest pex diameter and the smallest wattage and gpm output circulator you can get to do the job otherwise use the 3/4" pex and the small pump. You will get constant flow with turbulence and you really won't get much stratification. There are two Taco 007 circ's in my system and unless the boiler temps go down far enough they run 24-7. Compared to fossilfuel consumption it is a very green alternative.

 

[maplewoodshelby]

Not sure why your say "huh". All I am wanting to do is run from my boiler coil to my electric water heater. The water runs through the coil and thru the water heater in a loop keeping the water heater up to temp. Ive read many places that it is better to run pumps 24/7 to make them last longer but I am wandering what size pump I need for this and if running constantly will cost more than just keeping the electric water heater turned on. My original plan was to hook up a temp controller and when the hot water tank needs heat it kicks on. Unfortunately I cant figure out how to do it so I;m thinking of just hooking up a pump to run 24/7 and maybe adda timer for it to circulate at peak time to ensure hot water

 

[maplewoodshelby]

Thanks, My boiler is not a gasser and is burning 24/7 so losing heat at the tank is not expected. The boiler water will always be hotter than what I need in the tank. I will place valves in the lines so that I can switch back to electric during the summer

 

[DaveBP]

Not sure why your say “huh”

Not trying to be a smartass, though there are other times I would have to plead guilty.
I was just stunned over my first cup of coffee to see "reduce wear on the pump" as the reason to run it all the time

I can see how it might be expedient to run a circulator constantly for a number of reasons. If it's a tiny one (like a Grundfos 15-10, 25 watts) just the cost of an aquastat to control it might buy enough electricity to run it a long, long time. And since all that power ends up as heat, if it's in a room you want heated it's not 'wasted' power.

Let me be the first to give the standard warning to install a tempering valve on your water heater if there isn't one there now. With this kind of setup you can end up sending very hot water out the tap.

 

[maplewoodshelby]

Lots of people believe that stopping and starting pumps wears them out quicker. I know this to be true with large sump style pumps but I'm no expert on these pumps.
So any thoughts on what I could get away with with pump and pex size and have it work correctly

 

[DaveBP]

A Grundfos 15-58 on its slowest speed hooked up to 100' of 1/2" PEX will flow about 2GPM. Same with 3/4" PEX will go about 4GPM. Just to demonstrate what a big difference one pipe size can make.
A Taco 007 will be similar.

Be nice to get a pro in on this to give an experienced opinion on what you really can get away with. It will depend a lot on how much hot water you need at peak times. The convenience of the 3-speed circulators is that you can tweak the speed to help match your requirements.

 

[maplewoodshelby]

Thanks for that info.
This might be a dumb question but just wandering. Most folks that do this have the public wat coming into the tank and then circulate water from the boiler either thru a heat exchanger or boiler coil. In my case I use the boiler coil. Does the public water supply pressure at teh hot water tank have any affect on circulation between the boiler coil and hot water tank?

 

[sbleiweiss]

Put me in the category of people that believe that running a circulator 24/7 is a waste of power and money. A 50 watt (smaller than a 007 or 15-58) circulator running constantly will cost about $10 per month to run. The cost of a new circulator every few years would be paid for, but you will get to keep the money. I just ripped out my old oil boiler with a Taco 007 that has run intermittently for 25 years and still works fine.

Anyway, that is not the question. Since you are circulating potable water, it has oxygen in it. You need a pump that is bronze or stainless. They make pumps for this application with internal controls. This pump would do the trick, I have one in my system:
http://cgi.ebay.com/Taco-Bronze-Car...cmdZViewItemQQptZBI_Pumps?hash=item439c60a1cb

Since you are not trying to move a lot of heat in a short period of time, this small 006 pump and small pex would be adequate to keep the tank topped up with hot water.

I think a better setup is to re-plumb the hot water heater so that cold water from the street entered the boiler coil first and then the output of that coil went to the hot water heater. The line from boiler to tank would be whatever is used in your water system like 3/4 type L copper. You could then still use the above circulator to keep the hot water heater topped up with heat during the heating season. This setup would give you more hot water in a shorter period of time.

Regards,
Scott B.

 

[maplewoodshelby]

I had thought of that setup(running the water from street thru the boiler coil 1st and then on to the water heater) I can easily do that as the water line that feeds my boiler is right there. Would I then just tee into the street line at the boiler with the pex coming back from the bottom of my hot water tank to make my circulation loop? I can put a shut off valve on my existing street water coming into the tank so it can easily be turned back on in summer

 

[webie]

My only background here is I use to - (18years) heat my DHW from a coil in a old style boiler during the winter months because I too use to burn 24- 7 then. First plan on a mixer on the outlet of the water heater for all safety sake do that . Now my set up I only had to run about 10 feet and I used 1/2 copper . The best way I found to charge the storage was to pull from the bottom of the drain and return back to thru the cold water inlet . The reason I used 1/2 was that's all my coil size was and I believe my coil was like close to 30 ft so I don't think I would have gained much using 3/4 as the coil would reduce my flow anyways . The one thing you should consider is if like DaveBP figures are correct and you can charge your water heater with from cold water to boiler temp water at a rate of 2 GPM with a grundfos 15-58 pump on low that would recharge your water heater in about 31 minutes from Ice cold . OK here is the real life with me . I was running a bell & gossett 4 speed SLC-25 on low . I could charge my 30 gal water heater cold to scalding hot in 45 minutes . Remember too you will be extending your amount of hot water also because rather than being say 120 it will now be at your boiler temp of nearly 180 so chances of draining your water heater completely if you don't now will never happen . Now as far as running a pump 24-7 that may reduce wear so they say but I have a taco 007 supplying my 5 zones and it kicks on and off every time a zone calls for heat its been doing this for 9 years and it seems to be working fine along with the taco that's on my radiant that cycles every 10 to 30 minutes . The water pressure in the water heater will have no effect on the pump or the coil .
If it was me I would just put an aqua-stat on the supply line to stop and start the pump as temp and demand required but 24-7 will work so that's up to you .
I just had a wall switch , turned it on in the morning when I fired and turned it off when fired and went to bed at night . Heck you could put it on a timer if you wish .
You should use a stainless or brass pump as a cast iron pump may cause some rusty water .
My pump was cast iron , used too much hot water for it to have time to get rusty .........

 

[sbleiweiss]

Yes, you will need to add a T at the inlet to the coil in the boiler. You will need a second T at the water heater outlet that feeds the house. You may have a more convenient place to add this hot water T that is closer to the boiler. Anywhere in the hot water piping will work. When you are using the boiler coil as a pre-heat, you can leave it this way all year round. BTW: these recirc pumps have an internal check valve. If you use something else make sure it has one. It prevents water flowing directly from the cold pipe directly into the hot when someone opens a faucet.

In reality, the recirc pump can go anywhere that there is a cold water and hot water line, it does not need to run from the DHW tank to the boiler. Just know that you will be recirculating hot water back down a cold water pipe, so when you open the faucet you might get warm water when you expected cold. Could make installation easier though.

 

[maplewoodshelby]

webie,
Thanks for your info. You anywhere near Park Falls? I come up ther grouse hunting every so often. When you say aquastat on the supply line can you elaborate? How and where exactly is it attached and so forth. Any aquastat model you prefer? I'm new to this hot water thing but loving it. I did my boiler install with help from friend and this site and it is adequately heating 5000 sq ft and temps are running single digits right now so I'm not totally an idiot. I did get on the horn and found someone who can show me how to wire he circulator to the water heater so after the comments here I probably wont run 24/7

 

[maplewoodshelby]

Scott b, you lost me on that post but thansk for the previous

 

[webie]

You can run it 24-7 ,I just don't see that it has too . As far as an aqua-stat you will have to check with a supply company ,or someone may know a model number on this site , you will need one that breaks on temp rise there should be 2 styles available one that the sensor clamps on the pipe or the better one that uses a well where the sensor goes in , either will work .
Parkfalls way on the other side of the state I am on the other side north of Beer City If I find a

 

[Duetech]

You could probably run 10-15 pumps 24-7 for what it takes to run an element in your electric water heater and still save money. With your size of heater you may have two elements.

 

[maplewoodshelby]

I do have two elements and the wife takes long hot baths every day so I know its sucking the juice.
Anyway, I have a plan together. I have someone who understands wiring the circulator to the water heater thermostat and someone who has used pex so that is the plan.
One guy thats helping me says that the hot water from the boiler needs to enter into the bottom of the hot water heater in order to have a good supply of hot water. I was thinking that the hot water came in at the top (on the hot side) and circulated back out to the boiler from the bottom drain. Again this will be hooked up to the thermostat on the bottom element of the water heater which will kick the pump on when the water heater cools topping the heat up again

 

[Duetech]

"I was thinking that the hot water came in at the top (on the hot side) and circulated back out to the boiler from the bottom drain."

That would be best for consistant hot water supply and would direct fresh cold water towards the boiler for heating as most hot eater heaters have a drop pipe to inlet cold water. Feeding hot water into the bottom of the heater would cause an immediate thermal exchange and denegrate the quality of your hot water.

"Again this will be hooked up to the thermostat on the bottom element of the water heater which will kick the pump on when the water heater cools topping the heat up again"

If your pump is running 24-7 there will be no cooling except when water is being drawn from the tank. If your cold water feed was sent to the boiler and heated first your hot water tank would only be supplied with hot water and with the circulator running 24-7 the tank would be kept at the temperature of the boiler. Running that little pump 24-7 will send an immediate savings to your wallet compared to those heating elements.