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paappraiser
09-17-2007, 05:27 PM
Hi

Im new here and not a plumber by any imagination I am a real estate appraiser. I was doing a walk through on a multifamily house that was owned by a plumber. What he did was took your standard 30gallon hot water heaters and turned them into boilers for the radiators in the units (pumps on them and all). I asked him about it and he said that it was a lot cheaper than buying 6 new boilers. Basically he changed some valve, added the pump and some how got a thermostat on them.


Since then Ive seen this in a few other random buildings.

Questions
Is this safe, stupid or ? and very importantly 'How is this done?'

Thanks

Matt

Furd
09-17-2007, 06:08 PM
How it's done is quite easy. You remove the drain valve and use that tapping for the return water. The outlet tapping is used for the supply and the inlet tapping is plugged.

Is it safe? Not in my opinion and not in the opinion of many building officials. Many jurisdictions prohibit using domestic water heaters for space heating systems. Most manufacturers void any warranty for domestic water heaters used for space heating purposes.

leejosepho
09-17-2007, 07:20 PM
Is it safe? Not in my opinion and not in the opinion of many building officials.

Why not? What are the issues?

I ask because I have been planning to add a recirculation line and pump to feed a small heater in the kickboard area of the kitchen cabinets. The heater and pump would be thermostatically controlled, and the heater's blower has a low-limit control so it will not run unless the water is hot.

jimbo
09-17-2007, 07:29 PM
The issues are that domestic water heaters are not designed for the kind of duty cycle which they would likely see if used for heating. They will yield whatever the spec'd gallons per hour is, but if tasked to deliver that basically 24/7, there is no way that they will last. The burner components and the tank itself will "cook".

We do not see hot water heat out here, so I am quite uneducated in this area. But a question I would like to hear answered by some pros from back in "cold country" is this: when you put a WH in a closed system like a hot water heating loop, does that tank now require ASME cert, even though it is being operated at only 40,000 BTU, and fairly low pressure???

GrumpyPlumber
09-17-2007, 08:42 PM
30 gal water heater is about 30K btu's hour.
Low end boiler for small residential application 80-100K.
The BIG difference: recovery rate.
32,000 BTU's will heat 30 gallons of water from 40 to 130 degree's in about 45minutes.
That might possibly work in southern Texas, but not in the north.

jadnashua
09-18-2007, 08:00 AM
Most radiators are spec'ed to produce their stated output with 180-degree water; radiant floor uses a lower temp (around 120 or so depending on load and design). Depending on what you have, you'd never get the comfort level required if you were using it for radiators. The other big thing is the duty factor...a WH is not designed to run continously, which could be required in the cold of winter.

MACPLUMB
09-18-2007, 10:47 AM
I disagree to one point, if the water is used as closed system the water heater will last longer,
this is according to the mfg's,
MANY WATER HEATER MFG'S NOW MAKE UNITS THAT HAVE SIDE OUTLETS FOR THIS PURPOSE THIS ARE IN THE 50 GALLON ON UP RANGE!!
these are combo units for potable water and space heating

MACPLUMB. MASTERPLUMBER AND WATER HEATER SPECILIST

leejosepho
09-18-2007, 06:40 PM
... if the water is used as closed system the water heater will last longer ...

Does that mean a recirculation line can extend/enhance the life of a typical water heater?

The thing that comes to mind here is that a water heater in a house system with a recirculation line connected at its drain port might not always cycle as deeply as otherwise.

jadnashua
09-18-2007, 06:48 PM
In a potable water system, you are constantly inserting new water, with it's disolved contaminants, minerals, oxygen, etc. In a closed system, you've only got a finite amount, so things reach equilibrium quicker. You end up with water that isn't as reactive, thus it should last longer.

master plumber mark
09-19-2007, 03:43 AM
[quote=MACPLUMB]

I disagree to one point, if the water is used as closed system the water heater will last longer,
this is according to the mfg's,
MANY WATER HEATER MFG'S NOW MAKE UNITS THAT HAVE SIDE OUTLETS FOR THIS PURPOSE THIS ARE IN THE 50 GALLON ON UP RANGE!!
these are combo units for potable water and space heating

I have an outlet in my own home on my 75 gallon gas

but it is meant for going through a heat exchanger in my
forced air system on the furnace...


that 30 gallon heater will burn out and leak or will not keep up with the demand in a bitter frigid temp

paappraiser
09-20-2007, 06:00 PM
Hi thanks for the reply

The heaters were used in a 2500 Sf building. So there were 3 "boilers" total 1 for each unit. Does it get cold here yea im in Philadelphia.

Were they 30 gallon units, I don't know. I'm sure they no more than 40 mabey 50 gallon.

So what would you do to set for the thermometer? I'm curious really on the mechanics on the whole thing.

He did say that they would last quite a long time since they were in a closed loop. (My gas hot water boiler for my house is pushing near 50 years old)

GrumpyPlumber
09-20-2007, 06:33 PM
Water heaters just aren't designed to return enough BTU's that a heating system requires, they're also awfully inefficient compared to a boiler.
A relatively cheap boiler runs at 80% efficient, a water heater runs at 60%, you'll see it on the gas bill.

Think of it this way, it's February, 24 degree's outside, the zone kicks on with a full 50 gallon tank maxed @ 160 degree's (boilers run at 180).
As the zone runs it draws the heat from the tank, the tank will lose it's heat very quickly, depending on size of loop.
Once that tank has gone to room temp it's just heating with the circ running overtime and you now have a zone thats trying to compete with 24 degree's but takes 45 minutes to recover @ 130, nevermind 160.
Your tennants might not notice the higher gas bill, but they will notice it's cold.

shashalou
12-08-2007, 10:51 AM
I came across this discussion by chance and cant help commenting.

I live on the shore of Lake Ontario and have used a 30 gal 30000 btu water heater for all my heating and domestic needs in an 1100 sq ft home with minimal insulation, for well over 10 years.

The notions of inefficiency are false if the heater is located in heated space and the vent passes thru the building to the roof.

The notions of faster "wear out" or excessive condensation are false since the number of on off cycles is much less over the life of the heater and wear from expansion and contraction is thus minimized.

Scalding is no more of a problem than owning a dishwasher but can easily be solved with an old kitchen faucet as a mixing valve.

Recovery problems, although present in very fast outside temperature drops, are not what might be expected, since the pump runs continually. The thermostat is simply the delta t formula with a little help by manually adjusting the temperature at the heater.

Most recovery difficulty would be eliminated by correcting the very wide temperature differential (30 degrees) in the gas valve. If anyone knows of a valve with maybe a 10 degree differential that would fit a standard heater, I would sure appreciate knowing about it

Bill Arden
12-10-2007, 12:50 PM
1. The normal element in a hot water heater will get to hot for the antifreeze solution and this will cause bubbles. This means that you have to replace the elements with a "folded" element.

2. These bubbles can sit at the top of the tank depending on how the tank is plumbed. (The top should be the exit)

3. The antifreeze tends to turn to goo if there is a leak. This can cause the T&P valve to stick.

4. Most people don't put a big enough expansion tank on the system and this causes the T&P valve to leak a tiny amount. (See above for the result)

They are not allowed here, but I've found that they make small electric wall mount heaters that are designed to be used as boilers.

So Physics says that they can be used safely, but idiots have used them incorrectly and the results were bad. (See myth busters TV episode)

I've even thought about starting with a piece of steel pipe and making my own heater since I only need about 5Kw to heat up the concrete floor.

shashalou
12-10-2007, 01:19 PM
My system is not closed. Anti freeze is not necessary and air leaves via the domestic hot water taps.

pete c
12-14-2007, 10:42 AM
Air you also using this system for your potable hot water?

Yummy!

Not sure I'd wanna drink or shower in that stuff.

I have heard of using a single system for heating and potable hot water, but, I have also heard that some nasty critters brew in such setups.

jadnashua
12-14-2007, 11:45 AM
The efficiency of a heat exchanger is dependent on the surface area, the conductivity, the flow rates and the differences in temperature between the source and the destination. A potable water heater is usually not a good match for a heat exchanger since it is not normally run very hot. A typical boiler is often designed for 180-degree water. A WH is normally capped at 130, and that is potentially dangerous. Regardless of the heat source in the WH, you can't transfer all that heat in a typical heat exchanger unless it is huge to the secondary loop. Typical radiant infloor heat runs are in the 80-120 temperature range, depending on design. The burner in the WH is probably in the 800-1000 degree range, so it can transfer heat from the flame to the water fairly quickly. You have nowhere near that delta-T in your heat exchanger.

shashalou
12-14-2007, 12:46 PM
nasty critters brew in such setups.

I've heard that too, when the water is not moving. My heater operates as a basic air conditioner when it's not heating by piping new street water thru it.


A WH is normally capped at 130, and that is potentially dangerous.

All I have owned say 160 at the top end. Why is 130 dangerous?


you can't transfer all that heat in a typical heat exchanger unless it is huge to the secondary loop.

I dont understand that.


Typical radiant infloor heat runs are in the 80-120 temperature range, depending on design.

I guess that would depend on the volume of water per square
foot but in general I agree altho some people around here run them at 180. I'd like to get 120-130 with 1 ft of 1/2" pex per sq ft.


You have nowhere near that delta-T in your heat exchanger.

That's true but I dont understand why that's a problem as long as the burner stays lit. My problem is in the long downtime of the burner--the 30 deg differential of the thermostat in the tank.

jadnashua
12-14-2007, 07:57 PM
For the young or old where their skin is thin, 110 can give a second degree burn...130 is down right nasty. Raising the temperature does store more heat, but the higher it gets, the more likely someone could get hurt. In a commercial operation where sanitizing dishes is important, they'll use the higher temperatures, and if you have an older dishwasher that does not heat the water if it isn't hot enough, then you need to run the temp higher, but you need to be careful as if anyone ran hot full on, they could get burned. There's a way around that, use a high temp and then put a tempering valve to adjust it to a safe temperature. You get the higher temp for your primary loop, but keep it safe for the potable water chain.

You're using a heat exchanger to transfer heat to the secondary heating loop. The hotter the water is in the heat exchanger, the more can be transferred to the secondary. Think passing your hand through a candle or a blowtorch. If you have a string of 100 candles and you want to move across them at the same speed, you'll get a lot hotter than going through one, but if you have a few blowtorches, you can achieve the same result in a shorter array. In either case, the source is running full tilt. Running lower temperatures in the primary loop means you need a bigger heat exchanger to transfer the same amount of heat in the same time.

shashalou
12-14-2007, 08:25 PM
put a tempering valve to adjust it to a safe temperature.

I have an old kitchen faucet in reserve to use as a mixing valve. As yet, with anti scald showers and one handle faucets, I havent seen a need.


In either case, the source is running full tilt. Running lower temperatures in the primary loop means you need a bigger heat exchanger to transfer the same amount of heat in the same time.

Yes, but I dont understand why you have to transfer the same amount of heat in the same time--that's what a tank is for. If I have a problem, it's that the burner shuts off way before full tilt is reached. I suspect most of the problem is in the 30 deg differential in the gas valve thermostat.

frenchie
12-14-2007, 08:28 PM
I've heard that too, when the water is not moving. My heater operates as a basic air conditioner when it's not heating by piping new street water thru it.


When you go on vacation, do you get someone to come by & flush the system every now & then? I've only ever heard bad things about this setup, so I'm curious.

Oh, wait - You & I didn't have a related discussion on BT last year, did we?

leejosepho
12-15-2007, 04:46 AM
When you go on vacation, do you get someone to come by & flush the system every now & then?

I could be wrong, but I cannot imagine why that would be any more necessary than having someone come "flush the [plumbing] system" in a house without hydronic heat. In this kind of "open-direct" system, the heating components are never stagnant unless hot water *never* gets used anywhere in the house.
http://www.radiantec.com/systems-sources/systems.php

frenchie
12-15-2007, 06:04 AM
If the water doesn't get used for awhile because nobody's home, and you have a regular water system, the tank keeps the stored water hot enough to prevent nasties growing in it. Even so, there's occasional reports of legionella contamination in systems where the storage tank isn't kept hot enough...

Nobody cares if a closed hydronic system gets nasties, it's a closed system. You aren't drinking it, or showering in it. Also, the oxigen gets forced out of it after a few cycles, there's nothing for the nasties to feed on, and there's usually/probably antifreeze & other additives in it.

If the water doesn't get used for a while because nobody's home, and you have an open radiant setup, you're storing a bunch of water at ideal growth temp.

You should check out what the guys at heatinghelp.com have to say about radiantec - might make you think twice before linking anything from there. (Search the forum for "open radiant", as they don't name radiantec by name, because radiantec trolls the forum & threatens to sue & so on.)

Or just note that their open direct system, as designed, is non-code-compliant. At least here in NY, it would be illegal.

leejosepho
12-15-2007, 06:47 AM
If the water doesn't get used for a while because nobody's home, and you have an open radiant setup, you're storing a bunch of water at ideal growth temp.

Where, and/or how? Having a check valve and a pump in a cold-water supply line does not make any part of the system an incubator, and any hot water remaining in that line after a heat cycle will soon cool to the same overall ambient temperature being experienced by plumbing throughout the house.

leejosepho
12-15-2007, 07:03 AM
You should check out what the guys at heatinghelp.com have to say ...
(Search the forum for "open radiant" ...

I could not find a forum there, but I did find this:


The temperature requirements for healthy domestic hot water and the low temperature needs of your radiant floor are very different ...

That is not always the case.


... low water temperature (below 140 degrees) is conducive to bacteria growth ...

I have no idea how many radiant systems are fed by water below 140*, but mine certainly is not. Nevertheless, this discussion has got me to thinking a bit ...

I am preparing to install a radiant kickspace heater under the kitchen sink, and how to keep from having that heater become a seasonally-dormant "dead spot" in the overall plumbing has been a concern. I have a 3-way valve so the circulator pump can either warm the pipes or serve the heater, and I have been debating whether to have the hot water to the faucet come through the heater when it is not being used in order to keep its core "fresh" at all times ... and I believe that is what I will do. When the heater is on, the faucet will get its supply from ahead of the heater but from after the heater the remainder of the time. I would rather not have the heater "leaking heat" during the summer, but its blower will not come on unless the thermostat is up and demanding heat.

leejosepho
12-15-2007, 09:57 AM
I have a 3-way valve so the circulator pump can either warm the pipes or serve the heater ...

Oops! I just realized I will not need that valve, and that neither will the hot water to the faucet have to come through the heater. Rather, the heater core can be "refreshed" and will only "leak a little heat" when the manually-controlled recirculator warms the line.

frenchie
12-15-2007, 02:22 PM
I could not find a forum there

Click on "questions", from the main page. Best hydronic/radiant forum on the web.

Or try this:

http://forums.invision.net/index.cfm?CFApp=2




, but I did find this:


The temperature requirements for healthy domestic hot water and the low temperature needs of your radiant floor are very different ...

That is not always the case.


It usually is. Radiant systems tend to come in under 110.


I have no idea how many radiant systems are fed by water below 140*, but mine certainly is not. Nevertheless, this discussion has got me to thinking a bit ...

I am preparing to install a radiant kickspace heater under the kitchen sink, and how to keep from having that heater become a seasonally-dormant "dead spot" in the overall plumbing has been a concern. I have a 3-way valve so the circulator pump can either warm the pipes or serve the heater, and I have been debating whether to have the hot water to the faucet come through the heater when it is not being used in order to keep its core "fresh" at all times ... and I believe that is what I will do. When the heater is on, the faucet will get its supply from ahead of the heater but from after the heater the remainder of the time. I would rather not have the heater "leaking heat" during the summer, but its blower will not come on unless the thermostat is up and demanding heat.

Radiant kickspace heater? You mean hydronic, right?

Not all hot water heat is radiant, radiant refers to in-floor or in-wall heating, usually pretty low temp to not mess up the finishes. Hydronic systems use rads, generally run around 200... kickspace heaters are usually a hydronic coil, I don't know that dhw would be hot enough. Can you clarify?

leejosepho
12-16-2007, 06:08 AM
Radiant kickspace heater? You mean hydronic, right?

Not all hot water heat is radiant, radiant refers to in-floor or in-wall heating, usually pretty low temp to not mess up the finishes. Hydronic systems use rads, generally run around 200... kickspace heaters are usually a hydronic coil, I don't know that dhw would be hot enough. Can you clarify?

Yes, I should have said hydronic, and please pardon my confusion. I am far from being an expert on this stuff. I installed radiant electric wire in a bathroom floor last year and that works far better than just about anybody else seemed to believe it would -- it provides all the heat the bathroom needs -- and now I am doing my first hydronic trial.

The BTU output chart for this particular kickspace heater ranges from 2266 @ 160*F to 3391 @ 210*F with the blower running at its low speed, but the internal control for the blower will kick it in at 120*F and the literature for the heater indicates it will begin providing heat at 130*F. Overall, then, we have yet to see how much heat I will actually get from water going in at 140*F, and I do have the option of raising my DHW to 150*F.

shashalou
12-16-2007, 01:35 PM
I've only ever heard bad things about this setup, so I'm curious.

My systems have been in place in my residence and my cottage for almost 20 years. My residence is basically unoccupied for 5 months. I have no known problems with bacteria. The pump in one is located in the cold water line that feeds the heater and the kitchen without even a monoflo T and there is no warming of the kitchen cold, 12 feet away.


You & I didn't have a related discussion on BT last year, did we?

I talked over there briefly a few years ago without success.


Where, and/or how?

That question remains unanswered.


I have no idea how many radiant systems are fed by water below 140*, but mine certainly is not.

Mine seldom gets over 140 deg and my residence heater in the summer is lucky to get to 110.


how much heat I will actually get from water going in at 140*F

Not much, I'd say. I tried it unsuccessfully, with a little fan (noisy and the quietest I could find) behind a 10x10 radiator from a baseboard convector (I forgot what its called).

leejosepho
01-01-2008, 07:23 PM
Well, and in spite of some fitting issues I just found out about, my water heater drives this kickspace hydronic unit just fine! The water heater has no problem staying above 135*, and the air coming out under the cabinet stays right at 20* less than the water temperature.

shashalou
01-02-2008, 05:11 PM
I'm glad I didn't suggest that brooder lamp.

It's single digits outside, my heater is set at max, just before the burner fires the temp into the radiator is 123
the return is 98, after it runs awhile it levels at about 135 and 105. I need it to run hotter but the factory thermostat just wont let it do it. Anybody know of a finer control that can safely replace the standard water heater gas valve?

leejosepho
01-03-2008, 03:21 AM
It's single digits outside, my heater is set at max ...

Same here, but I heard we might get a heat wave next week!

Would it be possible for you to add an electric warming belt around the tank at the top of your heater? The cost to do so would not be great, it might be just enough to make the difference and all heat produced would remain inside.

shashalou
01-03-2008, 08:20 AM
blankets

the problem apparently occurs because the pump causes the water in the tank to mix rather than stratify--thus the temp of the water around the sensor is warmer than it ought to be and the burner wont fire. I already have a 6" blanket around the top and none near the bottom to cool the bottom faster.

therinnaiguy
01-03-2008, 10:05 AM
If the water heaters are used for both heat and hot water and are not isolated from each intended use, you are consuming your boiler water every time you open up the hot water faucet. Have you ever heard of Legionella?:eek:

leejosepho
01-03-2008, 01:26 PM
If the water heaters are used for both heat and hot water and are not isolated from each intended use, you are consuming your boiler water every time you open up the hot water faucet. Have you ever heard of Legionella?:eek:

Not to argue, but to try to understand: Please explain. Frenchie had said something similar:


If the water doesn't get used for awhile because nobody's home, and you have a regular water system, the tank keeps the stored water hot enough to prevent nasties growing in it. Even so, there's occasional reports of legionella contamination in systems where the storage tank isn't kept hot enough...

As I understand what he just said, the only specific issue there is the matter of temperature.

Frenchie then continued:


If the water doesn't get used for a while because nobody's home, and you have an open radiant setup, you're storing a bunch of water at ideal growth temp.

I have asked where in the system and how that would be as described, but an answer has yet to be offered ...

I have a typical plumbing system in my house: Water comes in from the well, some of it gets heated and all of it eventually comes out at a faucet or fixture somewhere. Along with that, I have a recirculation pump and line going back to the bottom of the water heater so you can push a button in the kitchen and warm the line to the faucet before drawing any water, and I am not aware of there being anything dangerous about that. And then, of course, I have the hydronic unit getting circulated water from the same line being used by the kitchen faucet, with that water then being pumped back to the water heater.

Where is the problem you believe you see? Just like in anybody's house, the hot water line going to the faucet gets hot and cools again several times a day, and the same can happen to the recirculation line.

The only possibility for stagnant or incubating water I can see would be if the recirculation line was hot, then cooled and was left dormant for an extended period of time.

Is that what you are talking about?

If so, and to avoid having any problem there, I plan to supply hot water to the washing machine from the water-heater end of that recirculation line to be sure it always stays fresh.