# Side arm vs plate heat exchanger for domestic hot water?



## Slick (Dec 10, 2008)

I see most guys on here using plate heat exchangers...my central boiler dealer seems to prefer side arm exhangers for domestic hot water....what are the pro's and cons to each for domestic hot water?


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## bassman (Dec 10, 2008)

side arm - slow
plate - fast 

search this and there is alot of discussion about it and all the ways of doing it.


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## tanker (Dec 11, 2008)

I,ve got a sidearm on a 50 gallon wh,2 teenagers still at home and never run out of hot water.That is,was my preference because cheaper and I live where water is very hard and would most likely plug a hx over time


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## Blazin (Dec 11, 2008)

Yep..the plate exchangers will plug pretty quick with hard water and should be cleaned yearly. The sidearms are'nt really effected by the hard water nearly at all. Plates do make faster heat but require a pump to circulate the water, where the sidearm works on convection and no pump is needed.
I have a 40gal hotwater tank with a sidearm and have never ran out of hot water either.


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## motoman3b (Dec 11, 2008)

Side arm was the way I had to go because of hard water but be sure to hook it up with unions so it can be removed to clean... had to clean mine after one year because settlement blocked the bottom of it!


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## oneoldbanjo (Dec 11, 2008)

I have installed both a Plate Exchanger and a sidearm - I didn't know which to use so I installed both. As it turns out this is waaaay overkill.

Plate Exchanger - This works instantly in heating my water as it enters the water heater and supplies all the hot water I ever need. I shut the heating elements off in my water heater and unless we are gone for days - the normal use is enough to keep hot water entering the water heater and we never run out of hot water. When we were gone from Thursday morning until Sunday night over the Thanksgiving weekend we returned to lukewarm water in the water heater. (I had the sidearm turned off as we were trying to extend the burn in the OWB as long as possible).

Sidearm - This works really well for keeping the water warm once it has entered the water heater. If you are using a lot of water over a short period of time it will probably not keep up, and it may be necessary to keep your water heater set at a temperature that will come on once you start using water faster than the sidearm can heat it. I have installed mine with a valve that I can shut off the flow from the water heater and prevent the thermosiphon from occurring. I did this as with the plate exchanger and the sidearm in operation our water gets very very hot, and when I am away and the OWB goes out I don't want the water heater providing energy to the OWB when the fire goes out - and in the summer I don't want some kind of thermosiphon going on with the running water heater and the out of service OWB.

I really don't think you need both of them as I installed - and choosing between the two I would probably use the Plate Exchanger. I will have to wait and see how long the hard water will take to plug up our exchanger, we have a hardness of 10 grains on our public water.

Blazin:

An extra pump is not required for a Heat Exchanger in my system. The domestic water coming into the water heater passes through the heat exchanger just before it goes into the water heater inlet - the force needed to push the water through the heat exchanger is the pressure on the water service line. The water from the OWB is pushed through the heat exchanger by the pump that brings the hot water into the house for the furnace, and it runs 24.7.


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## Butch(OH) (Dec 11, 2008)

The guys have pretty well nailed it. Disadvantage of the side arm is capacity, disadvantage of the plate is you have to keep the tank warm when not using any hot water. Side arm wouldn't make enough hot water for 5 of us and I added a plate to the loop this past summer but kept the side arm in the loop since I already owned it. The water heater is now shut off but we have a lot of money in both plus all the valves and unions. 
My opinion is 1-3 go with a side arm, more than that go with a plate. Hour long showers and clean freak wives will change those numbers


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## Slick (Dec 11, 2008)

Thanks guys and yep it sounds like I had the pro's and con's pretty much right in my head, you guys all just reinforced them  I like the concept of the plate better but I don't think I'll circulate enough water to keep the tank warm with one..I'm single with girlfriend that's over alot so could call it a 1.5 person house...I'm thinking the sidearm is better as the tank will always be hot waiting for us, doubt we'll drain that tank and need more hot water to often.


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## motoman3b (Dec 11, 2008)

Slick said:


> Thanks guys and yep it sounds like I had the pro's and con's pretty much right in my head, you guys all just reinforced them  I like the concept of the plate better but I don't think I'll circulate enough water to keep the tank warm with one..I'm single with girlfriend that's over alot so could call it a 1.5 person house...I'm thinking the sidearm is better as the tank will always be hot waiting for us, doubt we'll drain that tank and need more hot water to often.



One other thing I did to my sidearm heat exchanger was insulate it with some foil type bubble wrap and some pipe insulation. Dont know as this was really necessary but helps reduce water temp drain due to coolness of the basement


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## oneoldbanjo (Dec 11, 2008)

I insulated my sidearm and all the piping in the basement. The heat coming off the pipes was letting too much heat into the basement. I used the foam insulation with the adhesive on the seam and used the 1" stuff for all the piping, and I just stuck two of them together to cover the 2" pipe on the sidearm.


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## Slick (Dec 11, 2008)

Everyone using a mixing valve ontop of the water heater with their side arm? Anyone have a good diagram of hooking a side arm up? Central Boiler's are pretty good looking but I see several variations, thoughtI'd ask around.


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## Blazin (Dec 11, 2008)

Mines hooked up between the blow off on top and the drain on the bottom. I failed to note that I built my own it's a 2" outer pipe with the 3/4 running thru it 32" long and it has never run out of heat even after 3 loads of laundry and 2 showers before mine. I put a tempering valve in, but my hard water put the cabashe on that after a year. Just gotta remember to get the water temp dialed before you jump in the shower, as not to burn the :censored: out of you! I covered all my lines/pipes with the foam rap insulation....


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## Slick (Dec 12, 2008)

That brings up a good point I was also thinking of....who else has made their own side arm? Doesn't look like there is much to it...and at $100-140+ bucks I'm seeing them go for...looks like an inner and outer pipe and some T's soldered together?


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## oneoldbanjo (Dec 12, 2008)

The equipment list is basically a 5 foot length of 1" ID copper pipe, a 4 foot length of 2" ID copper pipe - and then two 2x1x1 tees. The only weird thing about the tees is that the 1" sides allow the pipe to slide completely through and don't have stops - and the 1" should be inline with the 2" so the pipe is centered in the 2" outer pipe. It takes a bit of heat to solder the 2" fittings but can be done with a good propane torch. You will then need to get the adapters to connect the PEX tubing to the heat exchanger and the copper and brass fittings to connect to the water heater. If you have the lines to the water heater go above the heater and connect to the top of the water heater you will need an air release valve to let any trapped air out.


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## Butch(OH) (Dec 12, 2008)

Slick said:


> That brings up a good point I was also thinking of....who else has made their own side arm? Doesn't look like there is much to it...and at $100-140+ bucks I'm seeing them go for...looks like an inner and outer pipe and some T's soldered together?



Ya better go price some copper tubing and fittings. The end fittings are special but available. When I priced it out I just bought one complete.


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## Slick (Dec 12, 2008)

Thanks, that's basically what I thought. The T's are what had me concerned...are you saying the 2-1-1 T does let the 1" inner pipe slide through it with no stop? I was afraid it had a stop and the inner pipe wouldn't slide though...wasn't sure how I was going to handle that...did you guys just manually open up the stop in the T to allow the inner pipe to slide through?


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## Slick (Dec 12, 2008)

Yeah good point Butch, I was pricing fittings as this thread has progressed and it's a bit cheaper to build it but it's close enought in price to almost just buy one and save the time...


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## Slick (Dec 12, 2008)

Side arm shopping...anyone seen or used a short one like this
http://cgi.ebay.com/Side-Arm-Heat-Exchanger-Outdoor-Furnace-Boiler-Stove_W0QQitemZ200287401338QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item200287401338&_trksid=p3911.c0.m14&_trkparms=72%3A1205%7C66%3A2%7C65%3A12%7C39%3A1%7C240%3A1318

I like the concept of more surface area inside the tube...seems really small though  I'm thinking it would mount in the middle of the tank vertically with a nice 45degree up and out of the exchanger back into the tank...might help with thermosiphoning instead of having to go horizontal like with a long exchanger. 

I only started thinking about this one as I need to get a water to air exchanger and have used this ebay seller before...might get them at the same time.


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## Jkebxjunke (Dec 12, 2008)

Slick said:


> Side arm shopping...anyone seen or used a short one like this
> http://cgi.ebay.com/Side-Arm-Heat-Exchanger-Outdoor-Furnace-Boiler-Stove_W0QQitemZ200287401338QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item200287401338&_trksid=p3911.c0.m14&_trkparms=72%3A1205%7C66%3A2%7C65%3A12%7C39%3A1%7C240%3A1318
> 
> I like the concept of more surface area inside the tube...seems really small though  I'm thinking it would mount in the middle of the tank vertically with a nice 45degree up and out of the exchanger back into the tank...might help with thermosiphoning instead of having to go horizontal like with a long exchanger.
> ...



I bought 2 of those.. ( one for each of my houses..) I havnt installed them yet.. they look well made
I am thinking that in my main house where its me, wife and 2 kids... I my use a FP on the incoming water to the DWH and the side arm to maintain the temp... now for the other house where it is just my dad... I may just use the side arm... as for the seller.. they seem to be great people to work with.


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## rx7145 (Dec 12, 2008)

Slick said:


> Side arm shopping...anyone seen or used a short one like this
> http://cgi.ebay.com/Side-Arm-Heat-Exchanger-Outdoor-Furnace-Boiler-Stove_W0QQitemZ200287401338QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item200287401338&_trksid=p3911.c0.m14&_trkparms=72%3A1205%7C66%3A2%7C65%3A12%7C39%3A1%7C240%3A1318
> 
> I like the concept of more surface area inside the tube...seems really small though  I'm thinking it would mount in the middle of the tank vertically with a nice 45degree up and out of the exchanger back into the tank...might help with thermosiphoning instead of having to go horizontal like with a long exchanger.
> ...



Looks like it should work good.


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## Mister Twister (Jan 26, 2009)

Blazin said:


> Yep..the plate exchangers will plug pretty quick with hard water and should be cleaned yearly. The sidearms are'nt really effected by the hard water nearly at all. Plates do make faster heat but require a pump to circulate the water, where the sidearm works on convection and no pump is needed.
> I have a 40gal hotwater tank with a sidearm and have never ran out of hot water either.



Do you have any pics of your setup? I have a fin enhanced sidearm and after 2-3 showers we have luke warm water. Takes a long time to recover after that I also have a 40 gal hot water heater. I am wondering if the way mine is setup the top of the sidearm is about 3 -4 inches above the entrance of the TP valve. That maybe slowing down the convection heating effect? Maybe I can find time to post a picture tonight and you guys can tell me what you think.


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## Butch(OH) (Jan 26, 2009)

Mister Twister said:


> Do you have any pics of your setup? I have a fin enhanced sidearm and after 2-3 showers we have luke warm water. Takes a long time to recover after that I also have a 40 gal hot water heater. I am wondering if the way mine is setup the top of the sidearm is about 3 -4 inches above the entrance of the TP valve. That maybe slowing down the convection heating effect? Maybe I can find time to post a picture tonight and you guys can tell me what you think.



You probably read my earlier post but I too had that problem. we have 4-5 in the house. I added a plate type and now have the best of both types, tank stays hot and plenty of capacity.


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## Jkebxjunke (Jan 26, 2009)

I have also heard that if you use a circ pump on the side arm you will get much faster recovery


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## Mister Twister (Jan 26, 2009)

Butch(OH) said:


> You probably read my earlier post but I too had that problem. we have 4-5 in the house. I added a plate type and now have the best of both types, tank stays hot and plenty of capacity.



Yes I have read your post and I was considering adding a 10 plate exchanger coming into my hot water tank. I just don't want to add a pump to solve my problem because that means more energy.(That was another idea to speed up recovery time which I think would work.)

I still question my install with the pipe 3 -4 inches over the T&P valve then back down into the tank. I have wondered about that since the install in fall maybe if I am working against the thermo-siphon effect.

Seems there are others that have a simple homemade sidearm and are happy with it. My fin enhanced side arm is supposed to transfer more heat 11,500 btus is the claim.


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## Slick (Jan 26, 2009)

Not to try and put the work on your shoulders, but there has been alot of talk around here about if the thermo-siphion is effected by the side arm entering above the tank and having to work it's way down....I think we'd all be curious to see what happens with a before/after test if your was adjusted to not enter to high  I know I went with the short e-bay one to not have to come back down into my tank..my sidearm is only about 18" long, it looked so small compared to what I see others having I was worried but my water is really hot and I don't seem to be making a dent in the hot water by doing laundry and showering at the same time.


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## Mister Twister (Jan 26, 2009)

Slick said:


> Not to try and put the work on your shoulders, but there has been alot of talk around here about if the thermo-siphion is effected by the side arm entering above the tank and having to work it's way down....I think we'd all be curious to see what happens with a before/after test if your was adjusted to not enter to high  I know I went with the short e-bay one to not have to come back down into my tank..my sidearm is only about 18" long, it looked so small compared to what I see others having I was worried but my water is really hot and I don't seem to be making a dent in the hot water by doing laundry and showering at the same time.



I guess the only way to know is lower it. That means it will be lower than the spigot coming out of the bottom where I have a Tee now. I don't think that would have any effect though. The cooler water should be able to drop lower with ease it is going over the top and back in the tank is the issue. Sounds like a weekend project to me maybe Saturday morning.....


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## oneoldbanjo (Jan 26, 2009)

Mr. Twister:

I think that lowering the sidearm below the water heater drain is fine. This is how I did mine:






I also believe that entering the water heater at the T&P valve on the side of the water heater is fine, just move the T&P valve as little as possible. Some claim that the water heater manufacturers will not approve this - and I agree that for liability reasons they should not agree to "messin around" with their stuff. I will post a picture of my revised T&P valve after I install a shorter one tonight.

I also agree that any distance you go above the water heater will cancel out an equal amount of the thermosiphon in your sidearm. If you go 6 inches above then you will be canceling the energy that 6 inches of your sidearm provided. It will still heat up the water - it just won't flow through as quickly and return as hot water to the tank. I also believe that you must have a way to vent any trapped air out of the portion of the system higher than the tank or the flow rate will be affected.

I also believe that tapping the top of the sidearm into the outflow line from the water heater has the effect of pulling cold water off the bottom of the water heater, running it quickly through the sidearm, and then discharging it into the domestic hot water line before it can be properly heated. If you have your system plumbed this way I suggest you check the temperature at the top of the sidearm before running any water.....and then turn the hot water on and check the temperature at the top while the hot water is flowing....I bet you will feel the water temperature drop considerably as the colder water runs through the sidearm.


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## Mister Twister (Jan 26, 2009)

oneoldbanjo said:


> Mr. Twister:
> 
> I think that lowering the sidearm below the water heater drain is fine. This is how I did mine:
> 
> ...




Wow thanks for the picture that is how I plan on re-arranging mine because my sidearm is to long. I opted to go a couple of inches above the T&P valve instead of going below the hot water tank. In hind sight I knew it was a bad idea and yes I have hot water just bad recovery time. And you are also absolutely correct on purging the air I had to crack my fittings and take an unexpected hot shower to get the thermo-siphon going because of trapped air. I love communicating with individuals on this site because it is very constructive.

By the way how many gallon tank is yours and do you ever run out of hot water?


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## oneoldbanjo (Jan 26, 2009)

Mr. Twister:

I have a 40 gallon water tank, and it is just my wife and I and we never run out of hot water. I have to tell you though.....that we also have a plate exchanger on the inlet to the water heater and it makes all the hot water we need. I added the sidearm to keep the water hot after it was inside the water heater - but the plate exchanger works so well that we can shut the sidearm off and the water takes a couple of days to cool down.

The really weird part of my sidearm is that I added a 90 elbow in the internal 1 inch pipe and external 2" pipe so that I could use all the pipe that came with my sidearm kit. You would have to build your sidearm this way from the start as you have to solder the 1 inch elbow to the 2 straight sections while it is inside the 2 inch elbow - I don't know how you could retrofit this bend.


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## Butch(OH) (Jan 26, 2009)

Mister Twister said:


> Yes I have read your post and I was considering adding a 10 plate exchanger coming into my hot water tank. I just don't want to add a pump to solve my problem because that means more energy.(That was another idea to speed up recovery time which I think would work.)
> 
> I still question my install with the pipe 3 -4 inches over the T&P valve then back down into the tank. I have wondered about that since the install in fall maybe if I am working against the thermo-siphon effect.
> 
> Seems there are others that have a simple homemade sidearm and are happy with it. My fin enhanced side arm is supposed to transfer more heat 11,500 btus is the claim.



Sorry if I am getting the wrong idea from that responce but I did not add a pump when I added the plate exchanger. My well pump pushes the domestic side and I put the plate exchanger in series with the sidearm on the boilerside. I could take some pics but they would be pretty meaningless as I have insulated averything and wrapped it to keep temps down in the basement.


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## Mister Twister (Jan 26, 2009)

oneoldbanjo said:


> Mr. Twister:
> 
> I have a 40 gallon water tank, and it is just my wife and I and we never run out of hot water. I have to tell you though.....that we also have a plate exchanger on the inlet to the water heater and it makes all the hot water we need. I added the sidearm to keep the water hot after it was inside the water heater - but the plate exchanger works so well that we can shut the sidearm off and the water takes a couple of days to cool down.
> 
> The really weird part of my sidearm is that I added a 90 elbow in the internal 1 inch pipe and external 2" pipe so that I could use all the pipe that came with my sidearm kit. You would have to build your sidearm this way from the start as you have to solder the 1 inch elbow to the 2 straight sections while it is inside the 2 inch elbow - I don't know how you could retrofit this bend.



How many plate exchanger did you use? I was looking at possibly adding a 10 plate to preheat my water and leave the sidearm to keep it warm.


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## oneoldbanjo (Jan 26, 2009)

Butch:

My system works the same as yours....without any additional pumps. My domestic water flows through the heat exchager plate and into the water heater. The sidearm flows domestic water by thermosiphon. The flow from my OWB starts with the Taco pump at the boiler, flows through the underground pipe and into the plate exchanger for the water heater, then through the sidearm, then to the furnace exchanger. Only one pump is requred and it is at the OWB.


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## Mister Twister (Jan 26, 2009)

Butch(OH) said:


> Sorry if I am getting the wrong idea from that responce but I did not add a pump when I added the plate exchanger. My well pump pushes the domestic side and I put the plate exchanger in series with the sidearm on the boilerside. I could take some pics but they would be pretty meaningless as I have insulated averything and wrapped it to keep temps down in the basement.



I understand completely thanks for your input.


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## Mister Twister (Jan 26, 2009)

*Pictures of my Sidearm*

Picture of my Fin Enhanced Sidearm installed on my water heater. I am thinking of lowering it so the thermo-siphon effect works better do you think that will help recovery time?


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## blakey (Jan 26, 2009)

I was initially surprised to see it is stainless, would it be as good as copper for heat transfer?


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## oneoldbanjo (Jan 27, 2009)

Mr. Twister:

Looking at your installation.....it would not surprise me if you have air pockets at the top of the loop. When I bought my sidearm it had an automatic air release valve that would install in a setup like yours, and it would automatically let out any air in the system.

Last night I revised my T&P valve. I had initially used the one from the water heater that had a long stem to reach through the insulation. Last night I removed that one and installed one that had a very short stem. I believe the probe now reaches back into the water heater as far as the original did, and it would be even better if I had been able to find a little shorter piece of pipe to fit between the water heater and the Tee.....but this was the shortest one that Home Depot had that would work.

This is the long stem T&P valve from the water heater:





This is the long stem T&P and the short stem replacement:





This is the short stem T&P installed:


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## gravelracing (Nov 11, 2010)

*How big of plate exchanger to use*

I believe this is an old thread but I am currently hooking up my hot water and believe I need to use a plate exchanger versus a side arm exchanger but dont know how big of plate exchanger to use, what have some of you used and had luck with?


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## coostv (Nov 11, 2010)

This is an old thread.

I have six people in my house and have a 5"x12" 10 plate exchanger. It does all we need so far. I have not seen 4 back to back showers with it yet, but it seems to be handling the demand just fine. It has only been a week so far, so time will tell. As long as I am not the fourth to need the shower I will be happy. LOL.


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## gravelracing (Nov 12, 2010)

*Plate exchanger*

Thanks for the info, how did you plumb it up? We very rarely take 4 showers back to back but when and if the time comes I want to have hot water enough to do it!


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## coostv (Nov 12, 2010)

This is how mine is plumbed in. On the right you see the copper lines for my DHW, inlet (cold) from the house on top and outlet on bottom into my water heater. On the left are the lines from the boiler, in from boiler on top and out to the heat exchanger in my furnace on bottom.

I put unions in on the copper lines for easy removal later.

If you can sweat a fitting it is no problem.


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## gravelracing (Nov 12, 2010)

So the use of hot water actually fills your hot water tank? Do you leave your hot water tank on low in case you dont use hot water often enough?


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## coostv (Nov 12, 2010)

Correct, it is refilled with hot water. With daily use I do not think it will ever come on. I currently just have it set to vacation, I have not heard it run once (power vent). If I can make it down to Harbor Freight in the next couple weeks I will buy an IR temp gun (have a coupon to get one for $26) just because I am curious to see what the temp of the pipe is entering the water heater. That and I would like to see what the difference is in and out of the exchanger on the boiler side.


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## gravelracing (Nov 13, 2010)

Thanks for the info, I ordered a plate exchanger yesterday, should have by Monday or Tuesday!! Will be very happy to have free hot water again!


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## Jmax (Dec 9, 2017)

I want to use side arm but have to use pressures relief opening on top of WH
I’m told this won’t work any thoughts?


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## NSMaple1 (Dec 9, 2017)

That's where mine is plumbed.


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