is it possible to use plate heat exchanger for domestic hot water

PeteA

@hot_rod
I am still going back and forth with my options if I can't repair my combi boiler and I think if I can't I'm going to install a direct vent cast iron for the heat since I am much more comfortable with the life cycle of parts and ongoing support for them compared to the combis, not trashing the combis, they are amazing pieces of technology but my experience is only so so due to the choice of the one installed by the previous property owner.
I was wondering if there are any plumbing configurations where instead of having a large storage tank of hot water if there is a way to tie a plate heat exchanger into a CI boiler for nearly instant hot water which would only need to be heated when the tap is open? The house is only occupied by one or two people at a time so there's not a huge hot water demand and I just throwing it out there to figure if I was to put in a boiler protection valve to quickly cycle up the couple of gallons of water inside the boiler to operating temperature if that would be similar to an on demand. I realize that this will have the boiler couple of gallons set to keep warm constantly but when I'm away I could always shut the system down while I am away and not use any fuel for either device. I looked in the idronics 19 and didn't notice any plate heat exchangers for the dedicated DHW system. I would of course install a thermostatic mixing valve to maximize the temp control and increase the available heat transfer from the boiler to the plates.

Just throwing it out there, I'm not committed to anything but I was wondering about it last night when I was going through all of my options.

Thanks
Pete

GroundUp

There are a few ways to go about this. A small electric water heater tank as a buffer with the HX in a series loop set up as a zone from the CI boiler would probably be the easiest and cheapest. Otherwise a simple flow switch like a combi uses, that could actuate a 3 way valve or zone circ to do the same thing without the tank.

jringel

Take a look at the Energy Kinetics Ascent Combi Plus. This seems to cover what you are looking for

PeteA

@jringel those look really sharp but way outside what I can spend

hot_rod

Yes, any boiler can be a combi by adding an external plate HX. You want at least 120,000 btu boiler to get 2 gpm or so continuously, boiler on priority

Sika and Harwill make the low flow, flow switches to turn on the boiler, pump and or zone valve.

Most combis have a fairly small HX a 5x10 eight or ten plate.

SuperTech

I was going to say the same thing about the Energy Kinetics Ascent. Much better than your run of the mill cast iron boiler, efficiency near 90% and with the reliability and long lifespan of a cast iron boiler. It might not be cheap, but nothing good is cheap. You might want to get quotes from a few places, I've seen EK boilers being sold in a pretty wild price range in my area. 

PeteA

Thanks @hot_rod really appreciate your feedback

PeteA

@SuperTech thanks I'll take a closer look and ask around

szwedj

@PeteA Since you are replacing a combi, my thought is that you may not have a chimney to vent into? If that is the case, an Ascent Plus Combi may be a cost effective option as it can be side wall vented using polypropylene.

PeteA

@szwedj the house actually does have a chimney that I would have to open and inspect. Like I indicated the combi was installed before I bought the house, the previous owner converted from oil to the gas fed combi so I have never had a reason up until now to open the seal on the chimney I am certainly open for options so I’ll also look into the combi you mentioned.
im not anti combi but I a little hesitant since my current position is that my manufacturer of the one I have installed is out of business and I am possible being forced to replace it due to lack of parts.
i am open to anything that not super complicated and has a good reputation. I just believe (and could be wrong) that a power vent cast iron with an external heat exchanger may be an easier setup to keep up with.

PeteA

@szwedj
actually I have looked into that model and it’s sharp looking and super efficient but it seems really pricey from the few places I’ve seen folks mention prices