Plate Vs Tube for DHW

Doing some reading lately on pro's and con's of tube sidearms and plate heat exchangers. Both are a way more affordable option for me but its different for everyone. As im reading it hits me... check the forum. I found a small topic from 2008 on the search but i don't think we ever had a pros - cons - review - advice topic spit out. I could be wrong but hell lets kick one off.

I dont run my boiler year round. It would be a waste for me. My DHW usage drops as we cook outside more often, paper vs normal dishware, more pool time so showers seem to roll back a bit etc.... SO why not add a DHW loop using a heat exchanger. I have 2 spare ports on the manifold, an extra pump ( boiler side) and the ability to do it myself.

For about 200-250$ i can add a 34inch sidearm. For about 300-350 i can add an incoming 20 plate style. The plates i know from industrial experience are way more susceptible to hard water and sediment. But they have more "ass" behind them. The tube in tube wont have the issues with hard water and sediment as the plate will but are slower to recover and still may need the electric elements in the water heater to kick on every now and again during high usage.

Lets have who i consider the first hand knowledge/real life applications guys shake out the skinny on this vs the industrial sales pitches.

I can’t help you with the pros and cons but I have a brand new 30 plate exchanger I could sell you much cheaper than new. I had been thinking of listing it for a while now. I don’t know if you will get a direct exchange rate fast enough for domestic hot water without a loop to a tank though.

Im not a thermodynamic professor but help me out, if you install a plate on the cold water line into a DHW tank, wont the thermal properties of a cooling tank and pressure equal out in temp ? I could be completely retarded in that statement.... hense why i ask you folks haha.

anthony7812 wrote: ↑

Sun. Jan. 19, 2020 4:51 pm

Im not a thermodynamic professor but help me out, if you install a plate on the cold water line into a DHW tank, wont the thermal properties of a cooling tank and pressure equal out in temp ? I could be completely retarded in that statement.... hense why i ask you folks haha.

That’s true. There are videos on YouTube that explain the physics. Domestic hot water requires a lot of btu’s in a short amount of time. You need a buffer or an indirect source for a bar and plate exchanger to meet the demand. We had a 100 plate running a consistent loop to our oil burner and even that fell short of a constant supply of hot water equal to the oil burner running without a heat call. A direct coil is superior. The next best thing is an indirect tank with a thermostat call on its own zone or a gas/electric water heater with a loop that buffers the costs or uses it as an indirect source. My opinion based on experience. A domestic coil cost nothing to run but if that falls short an indirect tank off the coil would be best.

Plate exchangers have their place, I believe DHW isn't one of them.

I use a 20 plate 80,000 btu water to water exchanger for our DHW, I feed into the cold side of electric hot water tank, it is switched off and is 40 gallons.

My boiler is a remote install, so short of buying a indirect heater this was my only option.

I have a sidearm exchanger on my DHW tank. It heats the water up well. We have an 80 gallon tank, so we really don’t run out of hot water even though recovery takes a bit longer. The only downfall I have experienced is this: we turn the electric back on during warm months...it is shut off while the boiler is running. Once the electric is on, the sidearm exchanger tends to draw heat out of the tank...it works in reverse. The hot water from the tank heats the cooler water in the boiler line in other words. This decreases the efficiency of the electric heater. I am willing to live with that considering the benefit of leaving the electric off for 6 months out of the year.

Service or isolation valves for anyone considering piping in a new one will curtail any reverse flow when boiler is in any off periods.

The thought for myself at the lowest cost for big bang would be a coil in the van wert that would be fed into the electric water heater. Cold in coil, hot out boiler coil into the cold side of the electric then the hot out of the electric feeds all the users. Goal would be reduce electric to almost nothing...

My point of this thread is a HVAC friend pushes the sidearm for my application and he has sold some for a few others using their outdoor wood eaters. I get its cake to slap a sidearm on, but reduced space with a plate might be better for some? Just kicken the ideas out for those who are searching for answers.