Help with heating system

[Steven Turetsky]

Maybe this isn't exacly inspecting, unless you want to consider it inspecting before it's done, rather than after.

I'm getting ready to install the heating/hot water system(s) in a house I've been building for the past few years.

I have a new (left over from a previous job) Weil-McLain CGI-5 for the heat, which consists of radiant heat in the slab, and baseboards throughout the remainder of the house. (except the bathroom will also be rediant heat beneath the floor.)

I also just purchased a Rinnai R75LSi for the domestic water.

My reason for the on demand as compared to a water storage tank is space limitations, I like the idea of shutting down the boiler in the summer, and not keeping 50 gallons hot 24/7.

When discussing the installation with Rinnai, they told me this unit had the capacity to heat the house too. I love the idea of more space saving, but don't feel comfortable with using the system for dual purpose.

My reasons are that;

1. Because the boiler will be shutdown in the summer, and the on demand will only fire up when called upon, it will be a savings.

2. Since there is no water storage like in a boiler's heat exchanger, and there is no cast iron heat exchanger to hold the heat while the system still circulates without firing, I feel the on demand system will have to constantly fire every moment the thermostat calls for heat.

By the way, Rinnai tells me that although that might be so, there is another factor to consider; the system will not have to work to heat the heat exchanger and additional water it holds hot.

I checked the efficiency of both units, they are about the same.

Like I said, I love saving the space, but the thought of the on demand always firing up, rattles me.

Any thoughts?

[Rod Butler]

Cool thread. Look forward to replying when back on my puter but wanted to tag this. . . .

[David Bell]

Once you decide to use an on demand for heating you are back to needing an indirect tank. The water going thru the tankless is either potable or non potable. Your domestic hw just becomes another zone.

[Rod Butler]

OK, a couple of issues. Your post was a little unclear in my mind so if my response seems skewed you'll understand.

First are you looking at an either/or scenario? If you are only going to use one heat source you will need a heat exchanger. Bottom line.

If you have a moderate to large home the capacity of either seems low to me. Not sure exactly in New York you are hailing from but I know it gets cold up there.

As far as heat storage the Weil boiler holds maybe 4 gallons at a time, not the 50 gallons that you suggest.

Sounds like a fun project, HTH.


FOLLOW UP:

I read a little bit more about the Rinnai unit and I think I would steer clear of using it for anything but very basic domestic water heating. It does NOT have the capacity to heat your home and I doubt very much that it is rated for use as a space water heater. Weil is a good brand name, many years of good record, and it is designed to provide hot water efficiently.

[Steven Turetsky]

I agree, and am not suprised about the initial negetivity. I've already decided that I prefer independant systems.

FYI When using a Rinnai for heating, the warranty drops from 10 to 3 years.

[Zibby Bujno]

Rinnai R75LSi is a modulating water heater. It means BTU output depends on demend, therefore useinf it for radiant heat is good idea. You don't need heat exchanger. Now if you need FHW and radiant then things get complecated as circulating water temp goes (2 different temps)

[David Bell]

If you are really interested in an efficient wall hung boiler, check out a Buderus model GB142. Uses natural gas or propane, direct vent, and comes with a pre-piped manifold with one circ.

[Tim Trexler]

I am all for using two wall-hung units, one for heating and one for DHW but I would not use one for both.

[Markus Keller]

I've put in more Rinnai tankless than any other brand. I like their units, controls, vent pipe and manifold better the others. Cost is better for the most part also. Good units no call backs. I wouldn't use it for heating though. Seems like it might be a bit much for the unit.
Don't know what the cold temps are like in your area but if it gets really cold you may want to consider a holding tank prior to the tankless unit. Some of the articles I've read state that very cold incoming water can significantly reduce gpm output. At yesterdays CE class instructor had a chart showing 8.5 gpm at 75 degree incoming cold water, 5 gpm at 45 degree water.
I removed our old holding tank (rusty, etc) and haven't replaced it yet. The difference was immediately noticeable.
- make sure your gas pipe is properly sized
- the Rinnai pipe manifold is very nice and makes pipe-in easy, runs about $140 around here, worth it though
- The Weil-Mclain, Buderus, Lochinvar, etc are all good units, depending on the size and layout of the house consider a couple of zones