I'm in hot water

[Jeff922]

Well, at least that's what's been on my mind for the last several days.  I've concluded that an open radiant system is going to work best for us which means I will be using one heat source (propane hot water heater) for our radiant heat and domestic hot water supply.  I'm building the Victoria's cottage with all the bump-outs and it has an overall floor space (1st and 2nd floor) of about 1180.  I ran a heat loss calculation and came up with 37,000Btus/hr (based on -25F outside).  So I need a propane hot water heater that has an Btu output of at least 40,000 for heating.  Here's my question:  How many Btu's/hr are needed for domestic hot water for a house with two people living in it? 

[ScottA]

A standard 50 gallon heater will meet your needs but you need to add a second tank with a loop (heat exchanger) in it so you have a reserve for when you take a long shower or something and the heat is on. The second tank acts like a battery to store extra heat. Also this keeps the water in your heating loop seperate from your domestic supply. Don't try to run the heat straight off the water heater unless you like luke warm showers in winter.

[Jeff922]

This is the system I'm planning on installing:

http://www.radiantcompany.com/system/open.shtml

They claim:  "But if the radiant circulators are running, will the floor steal hot water from my shower?

No. That's because our circulators are very low wattage, non self priming pumps. They can stir water around a radiant system, but they can't compete with normal domestic water pressure. As a result, domestic hot water uses always take precedence."

But you have me wondering Scott.  Do you know someone who had a bad experience with this set up?

[ScottA]

I've installed alot of radiant systems and I've never done it the way they have pictured. Maybe it'll work maybe it won't. I guess it depends on alot of factors such as how well your slab is insulated and how big the water heater is. In theory I supose the floor will act as a battery the same way a tank would except the water won't be nearly as hot. Your floor temp will be around 80 degrees where as your tank temp will be 115-120 degrees. I can tell you this much. If the floor ever gets cold it will take a long time to bring it up to tempature. During that time you won't get a hot shower at all. This is all infloor right, no baseboards?

[Jeff922]

Yeah it's all in floor.  Thanks for the input, definitely something I will consider.

[ScottA]

If you used a tankless WH I'd say it would probly work fine since a tankless can put out alot more BTU's than a conventional WH.

[JRR]

The first radiant systems I have seen, years ago, were in newly built houses in Germany.  Fairly smart folks, I believe.  Never saw a system there that was not separated ... one for circulated hot domestic water (approx 120 degrees F) ... one for circulated heating water and anti-freeze solution (approx 85 degrees F).  

The hot domestic water may well end up in tea or coffee.  Tastes pretty good.  No extra exposure to tubing.  No one ever made sick because some heat exchanger failed.

Hot water heaters just don't cost that much in my neck of the woods ... don't see the need for all the "simplication" at the expense of control and performance ... and perhaps good health.

[MountainDon]

I personally do not think I would want a single tank open system.

One reason is that I even disagree with turning down the temperature in a domestic hot water heater to 120 F as is recommended by so many in the effort to save on water heating costs. Legionnaires Disease, or Legeionellosis, is caused by "Legionella pneumophila, thrives in warm water. The organism is very temperature sensitive. Some countries, Canada included do not recommend setting the tank temperature below 140 F. It seems to me that running the hot/warm water through the radiant system simply expands the volume and surface area where the Legionella pneumophila can exist and multiply.  We use a super insulated tank and all showers are fitted with the anti scald valves.

* 70 to 80 °C (158 to 176 °F): Disinfection range
* At 66 °C (151 °F): Legionellae die within 2 minutes
* At 60 °C (140 °F): Legionellae die within 32 minutes
* At 55 °C (131 °F): Legionellae die within 5 to 6 hours
* Above 50 °C (122 °F): They can survive but do not multiply

* 35 to 46 °C (95 to 115 °F): Ideal growth range
* 20 to 50 °C (68 to 122 °F): Legionellae growth range
* Below 20 °C (68 °F): Legionellae can survive but are dormant

Most people who contract the disease get it by breathing in contaminated water droplets when in a shower or bath. The lower temperature water can also be an issue with dishwashers; too low a temperature does not kill bacteria there as well either.

Two, I worry about heating outages for prolonged periods. I would opt for a system where the radiant is totally separate and filled with the correct non toxic antifreeze.

My understanding is that a radiant only heater system can use water as low as 90 - 100 F for heating

[Jeff922]

You all have made some interesting points.  I will definitely take them into consideration.  One other thing I came across that has turned me off to the anti-freeze idea is that it is supposed to be a less efficient heat-transfer medium - 15% loss or something.  I was considering tankless units, but I've heard so much bad about them.  There was an article Consumer Reports that was very negative about tankless units.  Hummm...some thinking to do.  Thanks again.

[ScottA]

The only problems I've run into with tankless heaters is where they put them in an old house where the gas lines are too small and in many cases the water lines have calcium buildup to the point the flow is restricted. Low flow will prevent an tankless from comming on. This has been improved in recent years with more sensitive sensors to detect the flow. I have a tankless in my cabin and it works perfectly and takes up alot less space than a regular WH. Note I'm talking about gas heaters. Electric heaters are a joke.

[JRR]

............. anti-freeze idea is that it is supposed to be a less efficient heat-transfer medium - 15% loss or something...............

The anti-freeze solution might be a slightly less efficient heat-transfer medium...  but I assure you its nothing like a 15% loss ... it would take a lab procedure to measure the difference.  There are a few million automobiles running around that seem to prove it works fairly well.

Another thing to think about is the difference in volume of the heating system (rather large), compared to the domestic hot system (comparatively small).  In fact, if the house is small, and small diameter insulated domestic distribution tubing is used .... a daisy-chain layout can be made (with heavy usage on the very end), that is so efficient overall that a recirculation pump no longer makes much sense.  And a once-through system is the safest of all.

[JRR]

............. Note I'm talking about gas heaters. Electric heaters are a joke.............

I know of two close-by homes that were blown off the foundations ... along with some singed eyebrows ... because of gas fired water heaters.   And another friend torched himself when he was working on his car in the garage that also housed the piloted hot water heater.  Bet in all three cases, the folks would have rather had a good joke!

I currently use gas myself.

[UK4X4]

Here's some UK input

Almost every house runs gas boilers with water filled radiators. (Cost of electricity is high in the UK)

Then about 50 / 50 houses with a water tank for hot water and the rest with on demand hot water.

These days it would be rare to see an open system, almost all are closed loops with a small  expansion tank in the boiler its self
the fluid has anti freese and anti corrosive attributes.

On demand boilers we would normally plumb them in with 1" gas lines and 1" main flow lines to the showers- 15mm or 1/2" to taps etc

That way you have enough gas flow and enough water flow to provide a nice hot shower.

Cunningly though in the UK houses are small and the boilers are normally situated close to the bathroom.........yep we usually only have 1 !

As most had outhouses and the bathrooms only recently moved inside.............loosing the small bedroom as a norm- most being above the kitchen.

Boiler was either installed in the kitchen or bathroom above making the main lines short

Only in more recent houses you might have an onsuite if your lucky !

This is based on the prettymuch standard 3 bed semi- detached of which there are millions in the UK

My old house built in 1898 ish.....originally lime and sand sand cement 6" brick- 3 " air gap 6" brick - a fireplace in every room.

[Jeff922]

Again, thanks for the input you guys.  This morning, I'm studying the info presented on the web resource:

http://www.radiantdesigninstitute.com/

I'm weighing all the pros and cons of these different systems.  What's kind of funny is what started this whole heating issue is my electrical work.  I'm finalizing my electrical plans and needed to know what cables/circuits to run to the utility area.  With a slab on grade foundation, running wire after the fact isn't easy so I'm trying to plan ahead.  But I'm glad I've opened this whole can of worms now rather than later.  

[Jeff922]

MountainDon,  I've just done a little research on Legionellosis and I'm glad you brought it to my attention - it's nasty business.  I did come across this response by Radiantec in VT:

"Are there safety issues or Legionella bacteria problems associated with the domestic water heater based systems?

    * Domestic hot water systems compare very well with other heating systems and National code officials have seen fit to approve them. Radiant heating systems in general have significant health benefits. Low temperatures and low pressures are always good for safety. The "open direct system" is mechanically identical to so called "recirculation" systems which are very common and do not seem to be causing undue problems. Legionella bacteria cannot withstand temperatures above 115° F. You can always reduce the risk of contamination by bacteria by increasing the water temperature, but you will then increase the risk of scalding. It is our opinion that the risk of Legionnaire's disease in domestic hot water systems is "an emperor with no clothes" that is largely created by special interests groups in the heating industry. Legionnaire's disease is a reportable disease according to law and public health authorities make every effort to determine the cause when it appears. We are not aware of even a single case of Legionnaire's disease that was caused by a domestic hot water based heating system. If it were a real issue, there should be many. The National Center for Disease Control is a respected authority in these matters and the following link may provide useful information. http://www.cdc.gov/ncidod/dbmd/diseaseinfo/legionellosis_a.htm"


Which leaves me with one question;  if it's a non-issue, why has Radiantec brought it up in their FAQs page?  More studying to do...

[MountainDon]

Here's a source on Legionellosis I've had bookmarked for a while.

http://www.treehugger.com/files/2009/03/turning-down-water-heater-safe.php

and one from OHSA
http://www.osha.gov/dts/osta/otm/otm_iii/otm_iii_7.html
The ohsa doc notes that...
COMMON SOURCES OF CONTAMINATED WATER.

Water sources that frequently provide optimal conditions for growth of the organisms include:

--cooling towers, evaporative condensers, and fluid coolers that use evaporation to reject heat. These include many industrial processes that use water to remove excess heat;
--domestic hot-water systems with water heaters that operate below 60°C (140°F) and deliver water to taps below 50°C (122°F);
--humidifiers and decorative fountains that create a water spray and use water at temperatures favorable to growth;
--spas and whirlpools;
--dental water lines, which are frequently maintained at temperature above 20°C (68°F) and sometimes as warm as 37°C (98.6°F) for patient comfort; and
--other sources including stagnant water in fire sprinkler systems and warm water for eye washes and safety showers.

and more faq
http://www.osha.gov/dts/osta/otm/legionnaires/faq.html

[MountainDon]

Perhaps because I live in the rather dry desert I think about this more than some. That's because one of the joys of life in a low humidity climate is to stand in the hot shower and breath in the moist air.

[Jeff922]

Thanks MtnDon.  I'll check this stuff out.