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indirect as buffer

Here's the situation: If you wish, just scroll down to the BIG QUESTION below

So I have a customer with no backup heat source.  the entire house (1200 dn, 600 up) is taken care of by a solar high mass in floor system (read: solar heated 2'deep sandbox)

and a wood stove masonry stove.

the house will usually self maintain at about 50 degrees with no wood fire. 

the customer is re-fitting the upstairs as an apartment, and wants backup heat for the all house.

 the plans are as follows: upstairs: 3 panel radiators, one in main room (5000 btu), one in bathroom (possibly towell warmer 2000 btu) and one in the bedroom(3000 btu).  She would like each one upstairs zoned separately. 

Downstairs, there will be a fan convector (10,000) for space heating in the open middle of the house.

I see a few options that could work well for this system, and am looking for feedback, as in "throw it at the wall and see what sticks. "

the other caveat: we have really restricted space to work in.  3'-4' wide, 8' high.

1: size everything with low temperature water and use an AOSmith vertex tank style WH, with a flatplate HX to go to the heating system.  run the WH at 140 and reset down to whatever's necessary.  I have done this successfully with a couple of systems with really low water temps. 

2: TTP prestige excel all-in-one, and hope the mass of the internal tank will prevent short cycling. 


Here's the one I'm wondering about, from an academic standpoint as much as any other:  can i run a single primary loop thru a tank-in-tank indirect heater (think weil Mclean or triangle tube smart) and set the boiler reset curve between 130 and 160 for the radiators, activate the circulator on either the DHW call or heating call, and before the flow returns to the boiler, put closely spaced tees on the line back to the boiler, with a GF1555 alpha and uponor manifold with loop actuators.  I'll try to post a schematic shortly.  The goal is to buffer and produce adequate dhw in a tiny tiny footprint.

This seems like a best of several worlds option.  I'd probably be using a MC-50 or MC-90 if necessary for DHW load.




  • meplumber
    meplumber Member Posts: 678
    I did something very similar.

    I did something very similar.  It worked, but required a bit of controls magic with some 3-way zone valves.  Honestly, it took me 3 different configurations of the controls to land on the one that worked.  I will see if I can find my notes.  Contact me and I will try and email them to you.

    Good Luck.
  • Karl_Northwind
    Karl_Northwind Member Posts: 139
    upon further considerations

    it seems that I misread the specs for the excel, and it has 14 gallons of DHW, and would therefore meet my buffer needs and let me do crazy experimenting closer to home.

    I appreciate the advice and thoughts.  Ill still post the schematic when I'm drafting the other stuff, but it might be a bit.


This discussion has been closed.