Tankless propane fired water heater for in-floor radiant heat plus DHW.
Last Post 02 Dec 2014 09:02 AM by sailawayrb. 30 Replies.
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mmorelandUser is Offline
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18 Oct 2014 08:19 PM
I am replacing an oil fired 30 gal. Bock water heater that has been in service 26 years heating an in-floor radiant heating system as well as providing DHW for a 2 bath, 2100 SF wood framed residence. I want to switch to propane (we are in a rural setting and have no natural gas) and use a tankless heater. I would like to install the system myself having installed the existing one and being a retired general building contractor. I see that there are many heaters on the market, and I'm looking at only those that are modulating and condensing. I will need controls what will turn off the floor heat when there is demand for DHW and restore floor water circulation when no more hot water is needed. Are there any members of this forum who have practical experience with these heaters or can make a recommendation?
jonrUser is Offline
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20 Oct 2014 09:47 PM
Conventional wisdom is that a water heater won't last when used as a boiler and combining open loop DHW with heating (if that is what you have) will lead to legionella problems. So I'd like to hear why this "bad idea" evidently worked so well.
BadgerBoilerMNUser is Offline
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20 Oct 2014 10:01 PM
Longevity does not prove that the system worked well...
MA<br>www.badgerboilerservice.com
mmorelandUser is Offline
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21 Oct 2014 08:21 PM
This water heater did last far beyond its expected life. I put it in in 1988, and this week it began to leak. It's not an open system in that there is a heat exchanger between the heater and the floor. Two circulating pumps operate simultaneously to transfer water from the Bock heater (30 gallon reservoir) and water from the floor through the heat exchanger in opposite directions. The loop on the Bock side is perhaps twenty feet long in total, and I suppose that could be considered an open loop since the same water that comes out of our tap on the hot side is also run through that loop, but it's a small quantity of water that is always at a fairly high temperature. I don't know if that leads to illness or not, but we've been ok by luck or design for the last quarter century. Our water comes from a well, is stored in a 5000 gallon concrete holding tank, is aerated as it enters the tank and is not acidic, and that seems to me the reason we've managed to have the water heater last so long. I have no complaits as it has been a cost effective system providing good comfort to us all.
jonrUser is Offline
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22 Oct 2014 02:08 PM
Are your temperatures (when heating) actually low enough for a water heater to condense? Especially without outdoor reset.

Despite the fact that it worked well with the water heater, consider that by using the new unit for space heating, you will be doing far more "burner on" hours than the unit may be designed for.

Many people using oil or propane should consider air source heat pumps for at least some of their heating. But unfortunately, some countries (like the US) don't have many choices for air to water heat pumps.
mmorelandUser is Offline
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24 Oct 2014 04:21 PM
Hello jonr,  I can't answer your first question, but I know that the maximum inlet temperature for water to a Rheem tankless condensing-modulating heater is 120 degrees whether that comes in as a return from a hydronic heat exchanger or a solar storage pre-heat tank.  I can only assume that the heater is designed to function at that temperature, and I assume that the combustion gas exit temperatures are well over that, but I don't know any more about the functioning of the condensing heat exchanger.  The Rheem I was investigating is promoted as being capable of providing house heat as well as DHW as are a number of other similar heaters with very high maximum BTU outputs, and it is sold in conjunction with a water-to-air heat exchanger or air handler for space heating.  I was simply going to adapt it to a work with a water-to-water heat exchanger.  We were hoping to get away from having a tank of heated water sitting in the garage wasting energy, so we were willing to switch to propane.

It's an odd dilemma.  We'd like to burn a cleaner fuel, and most modern gas appliances seem to function in the 95% range of efficiency while our old, dirty Bock heater chugs away at 85%.  Diesel has 140k BTUs per gallon while propane only 98k (.85x140=119 vs .95x98=94; not a good trade-off), and the price per gallon isn't all that different at least in our neck of the country, so propane isn't financially attractive.  Still, we thought we'd go for it just to be a little cleaner, so I asked a local contractor to price the installation of a Triangle Tube tankless heater similar to the Rheem I'd been studying.  The price came back at $8250 to which we'd have to add $2000 for a 500 gallon propane tank, another $1000 for installation, and the project really lost its appeal, so I spent $1000 on a new 32 gallon Bock tank, switched the burner, aquastat and other gear over to it, and we're right where we were before the tank leaked. 

I'm happy to have spent relatively little cash to fix the problem, but we're still not happy to be burning oil, so I will take to heart your suggestion about an air source heat pump.  I'm building a small house across the drive from our residence, and I'm planning to install a ground source water-to-water heat pump, but I haven't ever explored, except very superficially, air source heat pumps, and that I will do.  We have a large solar array supporting both residences, and it produces excess electricity.  Actually, it serves three residences and a plug-in car, and so far still produces a slight annual excess of electricity, so depending on what an air source heat pump water heater requires for back up in cold weather, it seems worth looking into.  Mind you, it will have to produce the equivalent of about 70 million BTUs per year since it heats the house as well as the domestic hot water, but it gives me something new to explore.  Thanks for the suggestion.

Michael Moreland
Mendocino, CA
nightlightUser is Offline
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23 Nov 2014 12:47 AM
I have a tankless water heater Takaji using it to heat radiant and domestic. Works smoking well



for those that mumble something about some virus , legionella or something growing perhaps should look into something called UV Sterilizer - google it, do some re-search before you mumble something stupid.
You can 1. Circulate water at all times by setting a timer on one of the pumps to run for 60sec every 24 hours or 2 set up a UV filter on domestic line



I love the system considering that the boiler to heat your home cost $2-3k and a regular water heater $300-600. Where with a tankless i kill 2 birds with 1 shot for only $1300 i got heat and hot water




nightlightUser is Offline
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23 Nov 2014 12:53 AM
Posted By jonr on 22 Oct 2014 02:08 PM
you will be doing far more "burner on" hours than the unit may be designed for.


share some light on so called "BURN ON HOURS" copy paste some technical data where it says a burner is limited to so and so hours of use etc.. and what manufacture?????
sailawayrbUser is Offline
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23 Nov 2014 10:32 AM
Right, many people have proven that tankless can be made to work well. However, I wouldn't expect the tankless to last as long as well-made boiler expressly designed for space heating. For smaller spaces where some small amount of DHW is also required, the combos are not a bad option and likely win the ROI analysis.
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
jonrUser is Offline
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23 Nov 2014 10:41 AM
10 seconds with google leads to this (and this) where we see that one model has a 50% longer warranty when used only for hot water and another model has no warranty if it is used for heating. But I'm not making claims, I'm questioning why the OP's Bock unit lasted so long. Unlikely to be repeated luck, older technology, closed loop (perhaps less oxygen), a good brand, hours don't actually matter?
sailawayrbUser is Offline
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23 Nov 2014 01:07 PM
Not sure I would put too much stock in warranties. There is no shortage of companies that offer what sound like great warranties, but they likely won't be around long enough to honor them. It is likely better to buy from a trusted company that has gone the distance and has a good product and support reputation. And one also has to carefully consider the cost of the product versus the life expectancy. If you pay 4 times as much for a product that only lasts twice as long as the other product, you made the wrong choice with regard to ROI...
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
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23 Nov 2014 01:21 PM
I agree with the sailor...imagine.

If it sounds too good to be true...
MA<br>www.badgerboilerservice.com
sailawayrbUser is Offline
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23 Nov 2014 05:15 PM
All I can say is WOW!
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
nightlightUser is Offline
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23 Nov 2014 06:46 PM
So any of u have a tankless water heater for just domestic water ? to make some bull claims ?????

Do u know how it works ???

so if u have a family of 4-6 ppl and everyone takes a shower , dishes, washer , tap hot etc.... tankless rated for 30 years to surpass the regular water heater without any issues or parts to replace

now take a look at your boiler and see what it does how it operates and what happens when a thermostat kicks in



with a tankless thermostat kicked in tankless turned on hot water circulated 140deg tankless shut off temp dropped 110 it kicked back on to 140

no GAS being burned in idle as apposed to a boiler- well u can consider a wall hung boiler as well but the point is - with radiant heat no boiler is needed, tankless out performs beyond your imagination, there are tankless that push out 180 deg can use for baseboard considering that

I have a house with a boiler and baseboard heating and it idles and burns gas thermostat calls for heat it turns on for 2-7 min and shuts off OHH MY tankless can cover that - thats less time than someone took a shower or did a cycle of laundry
nightlightUser is Offline
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23 Nov 2014 06:55 PM
in the 1900 some one said "NOO way a plane to fly? take ppl across countries.... NOT POSSIBLE " a big peace of metal junk to take off into the air ? What ???? NOOO WAY....

and look now...


just cause some redneck plumber thats been using a boiler to heat his home for the past 30 years and refuses to utilize, learn and experiment with NEWer technology doesnt mean tankless is not a good, better choice.
I run tankless now for heating works amazing. Boiler? Whats that ??? Thats like Black and white TV - huh???? Perhaps compare a gas vehicle with an all electric one. Oil changes every 3000mi? spark plugs? O2 Sensors exhaust ??? what???? with electric non of that
sailawayrbUser is Offline
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23 Nov 2014 08:49 PM
All I can say is Wow again...LOL!
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
Blueridgecompany.comUser is Offline
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23 Nov 2014 09:17 PM
so,
If a plane could fly, ( just posing the possibility)
Could a boiler do both heat and isolated prioritized DHW on demand, have multiple temperature functions based on weather, function and form , have life cycle of 20+ years and a 15 year boiler core warranty and be 95% efficient with a design intent application, built in primary loop, low water cut off, and more?
Could the future be now?
Back to my cave,
Happy T day all,
Dan
Dan <br>BlueRidgeCompany.com
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23 Nov 2014 09:22 PM
"Happy T day"...as in happy turkey day...good one Dan, LOL!
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
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24 Nov 2014 10:21 AM
Posted By BadgerBoilerMN on 23 Nov 2014 01:21 PM
I agree with the sailor...imagine.

If it sounds too good to be true...
With this post...Everything I've ever believed on this forum was just called into question...   !!!

What's next? 

Cats sleeping with Dogs? 

LBear actually claiming Intus windows may not be worth the price? 

Dana endorsing the extensive use of XPS ?

Woah..  I need a beer.

(Nothing wrong with a little humor.  Thanks everyone for all the great information here...)


I was very interested to read that a tankless system may be a good idea in an area where you have less usage for DHW a (small bath room and kitchen) and you still want to use radiant heat.  Like a basement apartment.
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24 Nov 2014 12:01 PM
You guys are killing me and caused me to spill coffee on my keyboard, LOL!

Check this out:

BLT

Yes, we had a DIYer do exactly that for his garage/shop to be kept at 50-60F, with a small office to be kept at 70F that also required a small amount of DHW.  My son actually helped him with the design pro bono as time permitted because he wanted to hire us last year, but he was out of our jurisdiction (Illinois if I recall correctly) and we were fully booked up.  I should check in with him to see how well this approach worked out for him.
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
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