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[mildot1]

Sorry for my ignorance but what is the difference?

I am thinking plate exchanger. one feed to it then on to furnace. Does the sidearm require something different?

Pro and cons?

How do you size a plate exchanger 20/30/50 plate as to what you need for DHW and on to a forced air furnace?

Thanks in advance for any help!

[RSI]

A plate used as a preheater is the simplest setup and works best for most people. A sidearm will work better if very little how water is used.

20 plate is the most common for DHW. If you are right at the limit for restriction on your system you would want to use a 30 plate. Either will make plenty of hot water as long as you have enough flow on the boiler side.

You will want to get a 5x12" or 5x13" plate. There are small sizes too so don't just look at the number of plates.

[CountryBoyJohn]

 

[juddspaintballs]

If you have hard water, you may clog up the flat plate exchanger.  Make sure you install unions on all connections so you can remove it and de-gunk it even if your water is pristine. 

[RSI]

Sidearms can plug up too with hard water.

If you are running pex to the flat plate you can use swivel pex fittings and not need any additional unions to take it apart.

[mlappin]

Sidearms can plug up too with hard water.

Really? I have a hard time wrapping my head around water that hard.

[RSI]

I am guessing it partly happens due to taking water from the bottom of the tank where sediment builds up.
I fixed one that was just a simple 3/4" pipe inside a 1-1/2" shell that had about 4" plugged solid. The stuff was a hard as rock.

[llapanowski]

I had a side arm exchanger the last 3 years and it works fine, just the recovery time is not great.  Having 3 women in my house I was never able to turn the hot water tank off because of the slow recovery time.  This year I added a 10 plate exchanger to the system.  It works great, never run out of hot water.  Now the plate exchanger puts hot water into the tank and the side arm exchanger keeps it hot.  The hot water tank is now turned off, saving me considerable $$$ per month.  The plate exchanger cost like $90 on ebay (freeheat4u) and its already paid for itself, not to mention my wife can fill up the garden tub, my daughters can take showers and the washing machine and dishwasher can be on and we never run out of hot water. 

[Midnight Farms]

You don't just bypass the Water Tank when the plate exchanger is in the mix, and the boiler is fired?
Wouldn't this act as an on demand system basically then?
~Nick

[llapanowski]

Yeah I guess your right about bypassing the water heater.  What I have works so I'll leave it as is.  Guess my point is if I started from scratch I would definitely use the plate exchanger instead of the sidearm.

[userdk]

A plate used as a preheater is the simplest setup and works best for most people. A sidearm will work better if very little how water is used.

20 plate is the most common for DHW. If you are right at the limit for restriction on your system you would want to use a 30 plate. Either will make plenty of hot water as long as you have enough flow on the boiler side.

You will want to get a 5x12" or 5x13" plate. There are small sizes too so don't just look at the number of plates.

[cando attitude]

You don't just bypass the Water Tank when the plate exchanger is in the mix, and the boiler is fired?
Wouldn't this act as an on demand system basically then?
~Nick

Although this can be done, I would not recommend it as the  best practice, simply due to the fact that your hot water temperature would be directly proportional to your flow rate, i.e. the water temperature say when you're shaving with perhaps a slow to medium flow-rate coming out of the faucet would be much hotter than when one would perhaps have the faucet wide open when trying to fill a bath tub. 

When you install the exchanger before the tank, the hot water tank effectively acts like a surge tank, in the end, giving the homeowner a consistent hot water temperature.

Cando

[slimjim]

Very good post cando, thats a great point, way to think it out!

[Shrek1112]

Candy and Slim, does placing a mixing valve at the dhw outlet of the plate HX make a difference with the flow rate issue?

[cando attitude]

Although I personally have no experience with this, placing a mixing valve in the DHW line exiting the heat exchanger should remedy the scenario of inconsistent temperatures.  At least it would ensure that the water does not get too hot such that it would scald.

With my setup, I have not employed mixing valves.  I control the flow rate of water (on the boiler side) going to the heat exchanger for DHW.  By doing this, I make sure the water being put into the tank is no more that ~130 degrees.

Cando