Heat source

KansasFloorHeat

I moved back into the house I grew up in. We have been here coming up on 3yrs and we need to move on from our current radiant heat source. I have a Rinnai (propane) RUC98i that was installed BEFORE we knew our insurance company didn't like the wood burning boiler in the garage of the house we purchased. That boiler heats ONLY the water for our radiant floor. My 40 x 40 house is a shed and has 1000ft of 1/2" pex pipe in the floor with 12 lines going in and 12 lines coming out. The other half of the shed 40 x 40 does not have floor heat. My father put it in without any knowledge of anything back in 1981 but at that time it was plastic pipe (no insulation). It all broke as the house shifted and then they snaked 1/2' pex through. It all works fine. We had the wood boiler up and running last year the floor heats up nicely at 120degs water (pumps running 24 / 7) with a mixer. Our insurance wants the stove out of the garage because they aren't supposed to be in the garage (25ft from any structure). And we are ready to move on from burning wood. We HAVE to have a closed system. The lines in the floor are old and we can't drink that water as it is full of rust from the wood stove (no rust inhibitor was added to the water). Our Rinnai is capable of running Circ-Logic but I have some concerns. That concept is to run hot water in a loop so you don't have cold water turning on the faucet for the first 2mins. I thought maybe I could put a T or just hook into the hot port (where you would clean the unit) and run a line into an indirect hot water heater and back in to the cold port (where you would clean the unit). I think (if I researched this correctly) if you have a faucet that calls for water your Circ-Logic won't pump that cycle. So... If I ran the Rinnai through the coil of the indirect heater how would I get it to not run through when the water gets to 120 and say we are taking a shower. And would it decently heat my floor water if it was simply going through the heat coil. I thought I could make the pump run at night but then how long before the water was cold and we noticed it that day. Our Rinnai has a 13:1 turn down ratio. We are a family of 5 but this unit barely gets used. Yes we have 2 full baths but rarely are they running at the same time because 2 showers at the same time doesn't give 1 shower much water pressure. I have considered using indirect the other way and put the hot water in the tank for the house and the coil for the floor. Then I guess I would have more hot water for showers and may not notice a decrease in pressure. But I would have to use that set up all year round. On demand to indirect and then when the water needed warmed up it would run it through again? But then correct me if I am wrong the coil couldn't be on the bottom since that is where the cooler water is. Yes, I have thought about a heat exchanger but I am not impressed with the 20deg heat loss. Yes, I have questioned buying a new heat source but I really haven't come up with any great ideas. I like the HTP high efficiency crossover floor water heater but that is basically the same thing I have on the wall that I already paid for (Rinnai). I also thought about putting up a Laars on demand unit but we are talking about 10 gallons of water that heat our floors. It seems like a waste of money for 3 or 4 months out of the year. The wood burning stove in the garage was 175 gallons for a 10 gallon floor so obviously I am going for something more efficient. We also have a pellet stove on the other side of the house but that doesn't heat the concrete floors like radiant does. Long term I would like to ad on to this house and add more floor heat so I either need a short term solution or a long term solution that will heat more than 10gallons someday.

Oh, and for a bonus... winter started early this year.

Zman

Was the wood boiler in the garage rated for outdoor use only?

It seems like you are likely going to spend more time and money trying to retro a water heater to work as a boiler than it would take to design and install a new boiler and leave the hot water heater to heat your hot water as it was designed.

I am not sure why you are under the impression that more gallons makes the system less efficient. In many cases the opposite is true. More mass makes for less short cycling improving efficiency.

hot_rod

So you do or don't want to keep the Rinnai. You stated you are ready to move on , the rest of the post seems to be about using the Rinnai?

Jamie Hall

I admire your thinking outside the box. However... I also think you need to step back and start again.

First, how much heat do you need? Do a Manual J on the spaces and find out how much heat you actually need in each space.

Second, what are your fuel sources? LP? Natural gas? Oil? Electricity? Perhaps solar?

Now. The heating characteristics of a space and of domestic hot water are strikingly different. While there are units which, in some conditions, do a fair job of both, in most situations you will find that for the best efficiency and simplicity, you want a water heater designed for the purpose for domestic hot water, and a boiler, designed for the purpose, for your heating needs. Yes, you can use a hot water heater to run a radiant floor. It's rarely the best option.

KansasFloorHeat

According to the calculator 48,000 BTU. My fuel on the Rinnai is LP and it peaks out at 199,000. To clarify the wood burning boiler in the garage WAS heating the domestic water via an indirect water tank in the winter and using 220 electric in the summer (when the boiler was shut down). We weren't getting enough hot water for showers so we took that out and used that wood boiler to simply heat the floor and installed a Rinnai for domestic water. We have used that wood boiler for the floors until the insurance company told us to remove it (which they also told the previous owner but my father didn't care). Here is the rest of that. We HAD an unlimited supply of free firewood up until last year when the farm sold. We have been purchasing fire wood to feed it. My father who owned the house before me says if we want to move on to something cleaner and more efficient he would like that boiler back. But at his age he has also decided to move on from firewood and just sell it. We currently fill our propane tank maybe once a year for our domestic water use. So if we have to fill it twice or three times that would still be cheaper than buying fire wood. But our main concern is our Rinnai running all the time to heat the floors and then we will be unhappy with our domestic water again.

Buying a LP boiler to heat the floor (and leave our domestic water as is) isn't out of the question. I appreciate your feedback. I found this video the other day on YouTube https://www.youtube.com/watch?v=Q6DG1d2nNeE.

And this:

https://www.jlconline.com/how-to/plumbing/heating-a-home-with-a-tankless-water-heater_o

KansasFloorHeat

Let me try to clarify: Our LP Rinnai is tops out at 199,000 BTU but has a turndown ratio of 13:1. Our house is calculated at 48,000 BTU. We are done with firewood (for multiple reasons) and my father wants the wood boiler back. My options are the Rinnai that we have... or to purchase another LP unit to heat the floors.

I appreciate any feedback. I thought I could make it work but you are probably right. Just get a different unit.