radiant heating: boiler or water heater source?

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  #1  
Old 12-14-02, 06:18 PM
mlmatt
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Question radiant heating: boiler or water heater source?

We have a newer 16'x18' porch addition (6" walls, double pane w/storms, SSW exposure, tile floor) all set up for radiant heat (thermal barriers, plastic pipe set in, everything ready to g "plug and play" - but what to "plug it into?
we're stuck in a debate between using a boiler or relying on our 40-gal. water heater. What is the thinking now on water heaters doing double duty? In my on-line reading so far, there are a lot of strong opinions on this and not much discussion of exactly why. We're planning on buying a new gas water heater anyway - how might the extra demand on if change what we buy??
 
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Old 12-14-02, 07:29 PM
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mlmatt:

It is generally not permissible by code to connect a potable water supply to radiant heat and also not a good idea.

If you need average capacity from your tank for domestic hot water, you may find on colder days you will wind up taking a cold shower.

Perhaps you are reading about using a hw tank for radiant heating, where the domestic tank only is used for the floor heating water supply.
 
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Old 12-14-02, 07:50 PM
fjrachel
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I do believe you are talking about an 'Appollo' tm. type system. I've only seen them used in a forced air hydronic designs. As for radiant floor hot water heat??? I do not believe they would hold up.
 
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Old 12-14-02, 08:37 PM
mlmatt
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Question more on radiant heat water sources

My confusion continues. The <Radiant.com> web site loved the "open direct system" that has both functions in separate paths but using one water heater - but I agree that it makes sense to keep the water supplies separate . . . so maybe a llittle w/h for the porch's heat needs, and a regular w/h for dishwasher, showers, etc? I have doubts about using a boiler, since the high temps aren't necessary . . . Anyone agree?

How much water does the properly installed pex (? the tubing) hold for a room that size, anyway?

Thanks again
 
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Old 12-15-02, 12:06 PM
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Hot water heat

I dont think you will find a hot water heater that can have the recover for the amount of BTU's you will need for this room. Get the boiler ED
 
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Old 12-15-02, 12:19 PM
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Hey!

mlmatt:

Do you have an exact heat load calculation for this space.

If you don't you should do one or have someone do it for you, otherwise you could be throwing your money away on something that is improperly sized.

How about reading the anouncement at the top of this forum and provide every detail on your complete situation.

Maybe someone could then provide a better answer.

Thanx.
 
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Old 12-15-02, 01:51 PM
mlmatt
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Unhappy Boiler or waterheater

Jeez, I thought I was being detailed. Yes, I read the intro, thanks.

We laid this all in about five years ago - 300' of pex tubing, based on the heat load calcs provided by our HVAC folks. Then it became an "we can finish this ourselves" project . . . anyone know how that goes?

We're trying to catch up on new capabilities and system improvements as r. heating gets used more. That's when the discussion of water heaters vs. boilers heated up. It sounded like one unit could do it. That's why I'm asking some questions here.

I'll look into boilers.

Thanks. Any other thoughts?
 
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Old 12-15-02, 03:01 PM
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Sorry, lets try to clarify this.

mlmatt :

Your original question kinda got lost.

Your question was whether or not to hook up radiant heat to a domestic hot water tank.

This is what is not clear.

Do you intend to hook up the heating coils to a standard gas hw tank or a specially designed tank with two circuits, one for domestic hw and another for heat?

You cannot run the hw from a hw tank through pipes in the floor. They must be separate circuits and approved for this use.

Your choice would then be to purchase a special hw tank with two circuits or a separate boiler for the floor heat.
A boiler by the way does not especially heat the water to a high temp, in fact the temp setting for the floor heat will likely be much lower that the domestic hot water supply.

So having said all this I would say that you would be much better to purchase a small boiler for the floor heat.

Also, you will have to know the heating capacity required before you do anything.



Does this make sense?
 
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Old 12-15-02, 09:13 PM
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It might be important to know what type tubing you used. I have 300 feet of Wirsbo HEPEX tube in a concrete slab supplied by a 30 gallon oil fired water heater (much more output than gas or electric) for 3 years now. I am in Northeast PA and as far as I know, there is no code that prohibits it. I have been wrong a time or two so check it out yourself, but the system works. You must use a bronze circulator and make a provision to purge air but if you have the equipment and the desire to DIY, you only stand to lose a few bucks in materials and your time. Anything you remove if the idea flops you can use when you install the new boiler.
 
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Old 12-16-02, 04:50 AM
bugsmeso
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Also look into NU-heat....which is a fiberglass sheet with electrical wiring in it. We have installed it in small areas like yours and have had great results. They are on the i-net. Electric is just fine and not expensive to operate ...like all think
 
  #11  
Old 12-16-02, 11:36 AM
Brewbeer
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Are we talking about oil, gas or electric as the heat source?

There are pros and cons for both boilers and hot water heaters.

Boilers are more expensive than hot water heaters.

Boilers are (or can be) more efficient than hot water heaters.

Boilers last longer than hot water heaters.

Boilers generally produce hotter water than recommended for radiant floor heat. If you get a boiler, you will need a mixing device to temper the water. A hot water heater can be set to the correct temp.

You could get a boiler to heat both domestic hot water using an indirect fired storage tank and your radiant floor. ($$$)
 
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Old 12-16-02, 09:12 PM
mlmatt
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Thumbs up

Thanks for the input - a real big help.

The preferred heat source is gas but electric's available too if we have to. The pex ends are a straight shot (10') from the utility cluster in the basement (furnace/w/h).

Sounds like we'd be in better shape using a small boiler, since adding a second closed system on to the domestic w/h would be a chunk o' $$ too. That was the big question - if a boiler is overkill, vs. doing in the w/h by asking it to do something it's not really designed for.

Now I have some good information without the product hype or agendas.

Thanks.
 
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Old 12-17-02, 06:08 AM
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A gas 40 gallon gas water heater would do just fine for that porch. If you reduced the pressure in the radiant, it would probably last a very long time.

But my initial suggestion was to share the one you already have. Without isolation between the domestic hot water and the water in the radiant tube. Why would you need it? It is no different than having 300 feet of hot water pipe in your house. The tube will take 150 psi with no problem and 180 degrees (which you will never reach). Just use a bronze circulator. Check local codes first because some things that are mostly logical are prohibited in some localities.
 
  #14  
Old 12-29-02, 09:59 AM
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I've read this thread with enthusiasm hoping that an answer to my question could be found, but I'm still confused. Please let me explain my situation which is somewhat the same, somewhat different.

I have an older two-story home built in 1928. The heating system is currently a gas-fired steam boiler feeding a single pipe system to standard radiators. The current system works very well and is reasonably inexpensive to operate. (Our previous home had a hot-water system with a circulating pump, so we were very comfortable with the buying this home with the radiators still in service.)

We are about to start a kitchen renovation which involve removing several small walls to enlarge the actual kitchen and also expanding by adding an 8' x 10' mudroom directly off the kitchen. Oddly enough it had not occurred to me before we began planning the addition that the current kitchen was not heated -- no radiator. Now with the addition of the mudroom, which will have thre outside walls, we feel we need to heat the kitchen and mudroom space somehow.

We've eliminated the idea of using some sort of tubing system imbedded in the floor. The only ones we're aware of would require a considerable increase in the floor thinkness which is very undesireable, both from expense as well as asthetics standpoints.

When we remodeled the kitchen in our previous home the contractor sourced a great little hot-water unit that slid under the cabinets with a vent through the toe-kick. It had a thermistatically controlled blower that forced air over the coils once the water temperature rose to the proper temperature. We intend to use the same units in this kitchen. (We still need to find a source for these, so if anyone knows of these units and where we might find them, please drop me a note.)

Therein is the problem. Unless someone knows of a similar unit that will work on a steam-driven system, we'll need to have a hot-water source. I was planning to use a dedicated gas-fired water heater to supply these units. (we never intend to share this hot water with the main pottable water supply) Installing a boiler for this purpose seems like an over-kill to me. My assumption here is that I can get a 30 - 40 gal water heater and install it with the necessary plumbing for a lot less than a boiler.

This thread was not definative on the idea of using a water heater as a heat source. Someone here has done it successfully, others say it can't work.

To those who say it can work, can you please supply some sources of information to help me determine exactly what I'll need and how the system will need to be configured -- pumps, valves, water supply, etc.

To those who say it can't work, please say why and offer a suggestion for alternatives.

This is my first posting and I've attempted to provide as much information as possible. Please fell free to ask for additional information. Thanks you!!
 
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Old 12-29-02, 10:31 AM
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Using the water heater idea would be no different than using the hot water found in the boiler you now use for heat except that you would need a bronze circulator for use with fresh water.
You would just need to take water and return it to the boiler from below the water line. Some considerations are does your boiler maintain temperature all heating season? If not, there won't be hot water there for your toe space heater if the rest of the house isn't calling for heat. If you use the water heater, you have to take into acount the water temperature. Usually the output of the fan units are rated with 180 degree or hotter water entering. If you will have 130 or 140 degree water entering, you will have much less output from the heater. You may need more than one. If you were planning on doing it yourself, the water heater is a better plan. Piping near a steam boiler can require some special considerations and removing plugs from boilers that have been in use for many years can be next to impossible. If you get a feel for which way you want to go, I'm sure people here can guide you toward a successful project.
 
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Old 12-29-02, 10:53 PM
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Unhappy Radiant heating and hot water heaters

Wow. We learned that the city changed the building codes about three months ago so that hot water heaters CANNOT be used as a water source for radiant heating. What a discouraging change. A plumber I spoke with had to go to court to complete a job he was working on when the code change hit - no advance notice to the shops or the public. That also explains the problems we had in getting local shops interested in helping us out.

This fellow will work up schematics and compare them to what we came up with, get the materials and turn us loose. HE obviously can't install a W/H-supplied system, but since the "new" space was inspected and ok'd years ago, so it shouldn't be a problem if he advises us and we do the installation.

What a nasty blow to radiant heating in this cold-winter area.

I did learn that we are looking at a less efficient system because when we installed the system those years ago, the thermal barrier was only arounf the four sides (down 38") but not across the area of the floor itself, so there will be some heat loss downward. But we're still looking at a 55 degree minimum, so that's workable.

Thanks for the advice throughout - it kept me working to find a solution. Will keep you posted on the progress and results.
 
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Old 12-30-02, 10:16 AM
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For steam systems, if the demand is large you can go to http://www.heatinghelp.com/heating_howcome6.cfm and when you start to scroll down you will see a diagram and model number, make of a unit that will solve your problem. It will also answer many of the questions you are asking for. There is also someone on that site that can answer questions too.

If the demand is not that large and can be adapted to a steam system, you can go to http://www.radiantec.com and look at "pricing". Then click on "Individual Components and their prices". When you scroll down you are going to see mixers and exchangers. Excellent for small additions where wall and floor radiant systems are used. Wall systems are usually used in bathrooms and are very common in Europe.

Alternative to all this is a supplementary system. This works well and is very cost effective to buy and to operate, if it is not used as the primary heat source. You can go to http://www.Nuheat.com

If this does not satify you, I know a few more alternatives.
 
  #18  
Old 12-31-02, 03:09 PM
Coady
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More Questions

I have a hydronic system that I am just getting up & working, and have been enjoying the responses to the queries in this discussion.
What the plumber and I would like to know is
1) how is the water hooked up to the 3 way mixing value... do I need any input from the cold line (from the well?).
2) what does the pump do? does it just reduce the pressure from the system? or does it just induce flow?
thanks for your input..
 
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Old 12-31-02, 03:22 PM
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To try to answer your questions (in reverse), the pump circulates water through the radiant loop. Because you boiler operates at a higher temperature than you want in your radiant loop, you need to mix some colder water with the boilers hotter water to temper it. Enter the 3 way valve. The outlet of the 3 way valve will lead to your circulator and then through the radiant loop. One inlet of the 3 way is direct from the boiler. The other inlet is return water from the heating system, preferably including water from the radiant loop because it will be cold enough to temper 200 degree water down to 120 or whatever you want in the radiant loop. Is your valve thermally activated or manual or motorized? I usually use a 4 way valve but for one loop, you are on the right track.

No fresh water (from your well) is added anywhere. Your hydronic system is a closed loop. Once it is filled and vented, if we lived in a perfect world, you could take off the fresh water feed pipe and cap it forever. Just an example to give you a mental picture.
 
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Old 12-31-02, 05:37 PM
Coady
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Yeap!

So the three way valve, 'a' is the hot water from the boiler the 'b' is the return? Is this correct?
 
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Old 12-31-02, 05:40 PM
Coady
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Also the the floor could also be used in the summer to 'air condition' the area with cold water only, is this correct?
 
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Old 12-31-02, 05:44 PM
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home work

You will make the floor sweat if you put the cold water in it in the summer time
 
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Old 12-31-02, 06:01 PM
Coady
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But that wouldn't bother the system or the floor, a dehumidifier would dispose of the moisture...? right?
 
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Old 01-01-03, 10:41 AM
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WRONG

The cool floor would work as the dehumidifier and be wet all the time. Been there done that ED
 
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Old 01-01-03, 11:09 AM
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Coady:

Ed is right. Running cold water through the floor would make a mess of things.

You would create a mold and crawly bug farm.
 
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Old 01-01-03, 02:54 PM
Coady
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What if there is an air conditioner running as well..... same problem?
Would the a/c not deal with the dampness, and also the a/c would be running less if there was cold water being pushed through the concrete basement floor?
 
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Old 01-01-03, 03:11 PM
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Please. you guys are trying to reinvent the wheel. As a previous reply stated. Been there. Done that. FORGET IT. You will do nothing but create problems. Others of us who actually have devoted our lives to HVAC and new bright ideas have looked for a new way to heat, cool, make hot water, you name it, and every good idea has been tried or investigated and it is enough work to experiment if you have the tools and basic knowledge. If you are just bustin into the field, let us save you some headaches. It won't work. Not without side effects that far exceed the benefits.

I have a stream running by my house and I tried fresh water fan coil units. Go get a second job at McDonalds and pay the electric bill for the regular air conditioner.

I don' want to discourage a blossoming Einstein but this aint no Monster Garage. You will want your creation to last more than a week.
 
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Old 01-01-03, 03:24 PM
Coady
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Okay, I think I got your position. .. well understood, and I can tell you I am not into reinventing anything, where I live to do this kind of heating is so right field anyway!!!! I had no intention of radiant heating when the bulldoser broke ground in 1996 ... it was a 'heating engineer that convinced me to do this... then!!!!!!!!! he bailed... since thien I have been hiring a plumber heating expert about 1 every other year to get this thing done. Now that I have found someone to experiment with this to get it going I am into expanding it to its' 'full' potential.... so please bare with me while I ask some of the most ridiculous questions to you experts.... beleive me I am grateful.
I really don't want to throw good money after bad.... so your opinions are well listened to.
So the next stupid thing I am asking, is that I have been told to let the cooler water run thro the system even in the warmer months.... is this so?
 
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Old 01-01-03, 04:09 PM
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If you put water through your boiler that causes condensation in your boiler, you will wreck it so fast you won't know what happened. So you can circulate whatever you want through your radiant loop but keep cool water out of the boiler if it is shut down. A true high-tech radiant system measures outdoor temp and indoor temp and varies the water temp in the radiant loop based on the difference between the two. On a day when ot is 50 deg. outside you might only need 95 deg. water going through the loop. On a 10 deg. day you might need 135 deg. water. If you have the setpoint control and a motorized 4 way mixing valve, you are good to go. But be prepared to shell out $450 for the control and another $300 to motorize the mix valve. Big $ to fine tune what can be done with a small amount of human interaction as seasons change.

Your questions are in no way ridiculous but I want to deter you from making any big mistakes. We can hash right here for free and when you know exactly what you want to do, you can go for it with gusto.

By all means think outside the box. Life is no fun in the box. But in the same way, don't box yourself in with bad choices.
 
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Old 01-01-03, 04:20 PM
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A bit off track but that's ok.

mlmatt:

I hope you have had your original question answered to your satisfaction.

Coady:

Firstly, your questions are not stupid, in fact they exersize our brains to be able to explain something that maybe we are too familiar with.

As far as running cool liquid through your floor...........it's all about dewpoint temperature.

The dewpoint temperature is the temp at which condensation will form.
In order to be of some benefit the temperature of the floor will have to be well below the dewpoint temperature.
This is why anything that is used for comfort cooling has a drain pan under the cooling coil, plate, surface or whatever.

I assume you will be occupying this space and wouldn't want to live with the resulting dampness.
No matter which way you spin this, dewpoint or lower will be damp.

I havn't personally seen it but was told of a packing house that put chilled water in the floor to help with cooling load.
 
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Old 01-01-03, 04:57 PM
Coady
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Okay, well understood, no cold water in the summer months. thanks!
So here is where I am at, I have the tubes connected via the hot water tank. So what I need to know is whether the cold water should be attached to the return pipe into the mixing valve? I am thinking not, also I think the plumber has the piping to the mixing valve backwards. I think the mixing valve 'A' intake should be the return and the 'B' intake should be the hot water.
 
  #32  
Old 01-01-03, 06:58 PM
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The information for connecting the 3 way valve should come with the valve. I would not hazard a guess as to port configuration. Even if you don't have the original paperwork, you can probably get the information on the internet.
 
  #33  
Old 01-02-03, 12:15 AM
mlmatt
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Thumbs up Radiant heat questions answered

I think we're set for nw - at least until the next stage begins. Might be back then!
Thanks for the advice.
 
 

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