Need shop heat advice

I really don't understand why you are using a hot water heater to run radiant space heating. What you really need is a small gas boiler with a propane burner assembly. I they make some with less than 100,000 btu output, about the size of a breadbox. Heating a room with a hot water heater isn't the best way to do the job in the first place, not to mention your taking all that yucky heating loop water and comingling it with your domestic supply, can we say backflow preventer?

Kinda comical to see the bunch of mechanics here claim that a hot water heater has no standby losses, since it only loses heat to the room. Then we jump to the conclusion that the contractor's greed must be the reason for wanting to sell a tankless heater.

Losses up the flue is one of the biggest standby losses.

Incidentally it is one of the reasons why oilheat is inherently more efficient than gas, since the retention head oil burner greatly reduces standby losses by convection of air cooling the contents of a boiler/furnace as compared to an atmospheric gas burner.

Then I read in the Sunday New York Times business section where some nitwit is touting geothermal heat pumps. Ahhhh, tell me another fairy tale Santa. Its an old saw in how the media likes to offer false hope to the uninformed so they will keep buying the rag.

Tony

How does passing it through a few more feet of pipe make it "yucky" compared to the miles that it passed through on the way from the water works?

So how much does a current production energy-star rated water heater lose up the flue, and how does that compare to the amount that another type of heating device loses up the flue?

According to DOE both oil and gas furnaces are available with efficiencies in excess of 95%, with neither seeming to have any advantage in that department. Looks like you're working with old data.

Uh, what do you perceive to be the problem with geothermal heat pumps?

It looks to me like you're stuck in the '50s or something.

Simple answer? Initial Cost! A gas water heater can be bought by anyone for around $400. A gas boiler is not as easy to obtain, generally you need to buy it from a HVAC company, unless you have some connections, and a boiler will run $1500 and up, depending on what you get. Put the cost of each into the equation and in a moderate climate the water heater may come out on top! Greg

small gas boilers are under $1000, are easily obtained at any plumbing supply. Boilers are more efficient than water heaters.Water heaters are designed to heat potable drinking water, boilers are designed for space heating. When you consider the lifespan of a boiler is 4x that of a water heater, (cast iron vs. thin enamel steel) the boiler is the winner. oh, and don't forget to replace that anode in your water heater.

Tony

Well, in my experience as a licensed master plumber, try opening the boiler c*ck on a boiler and notice the brown water coming out. Actually thats the good stuff, because the oxygen in the water has reacted with the metal in the boiler & piping, been consumed, and corrosion stops at that point. Intoduce fresh water into the system and corrosion starts again. But I wouldn't want to drink it. The difference between the water in the street and the water in your heating pipes, about 120 degF.

That wasn't the issue. The prior posters were making incorrect statements about standby losses. As far as I know the DOE doesn't directly rate heating appliances for standby losses. I don't think AFUE rating calculations for boilers are comparable to water heaters, as they serve different functions. AFUE is a seasonal efficicency rating when it comes boilers.

Nope, not old data. I was at the last heating symposium at Brookhaven National Lab Brookhaven Long Island 2005. It's nice to hype 95%, but to really get over 90% you enter the realm of condensing boilers, which means a direct vented system as opposed to a conventional chimmny. Most gas boilers installed today are around 78% ~85%. Some gas boilers less than that. Some local building codes do not permit direct vented heating systems, NYC for instance.

It's just common sense that you can't heat your house with 45 degF ground water for a lower cost than burning fuel in a conventional boiler/furnace. Maybe aircondition it with a chiller system, i'll buy that.

Now if I could tap into a hot water spring, or lived near a volcano, then I would give geothermal heating a try!!!

Gee, maybe that's why i like watching Honeymooners reruns so much. I hold 5+ licenses for master plumber, boiler inspector unlimited horsepower NYC, oil burner installer all fuels NYC unlimited gallons per hour. And your HVAC background?

Tony

Using the same water heater for DHW would definitely require isolation via a heat exchanger of some type. The hot water heater would have to be used like a boiler, it would not be available for direct production of domestic hot water.

Oil burners also have a greater combustion efficiency than naturally aspirated gas, even before considering standby losses.

Geothermal has limited applications. You can take advantage of a COP "coefficient of performance" which allows you to extract more BTU's than you expend, but using electricity costs several times more than oil or gas, so there is no net gain economically on the heating side. Cooling is a different story.

But the OP already has the water heater purchased, installed and in service. So until it fails from old age, it's a moot point, as there is no payback for yanking out a working unit to install a boiler.

If the equipment costs three to four times as much up front, even with the longer service life it has to save a LOT of energy to make it economically viable for smaller systems. The small boiler needs the same gas controls or oil burner, flame safeties, water level safeties, etc. hung off the front that a big boiler takes, so the small ones are almost as expensive as the large ones. Only the orifice in the burner is changed to control the firing rate.

For heating a large house to comfort levels 24/7/365, yes, you want to use a real boiler - the system at the root of this discussion is for a small detached shop building where the primary duty is freeze protection and rust prevention, and it's cranked up for comfort only for short periods.

Here in Southern California where the weather is mild and heat needs low, they've built 100+ unit Condo buildings with Studio and 1-bedroom units heated by the domestic gas potable water heater, a Grundfos circ pump and a fan coil. Even with the losses in the water heater, the gas heat still beats the efficiency of a Heat Pump, and it trounces the holy heck out of electric resistance heat.

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Just out of curiosity, what's the matter with condensing boilers and direct venting systems in your neck of the woods. I fitted my balanced flue condensing boiler (stainless primary and aluminium secondary and tertiary heat exchangers with entirely copper water path) 8 years ago and have been very happy with it, although my gas price/Btu is probably a lot more than yours.

Mark Rand (in the UK) RTFM

Sure they are easily obtained, but by Joe Homeowner? You are in the business, so no problem for you. In my area unless you have a heating, or plumbing license you need to buy from a HVAC company because the wholesale house will toss you out the door. How many do you SELL for under $1000?? My bet not too many go out your door for less than $1500, unless it is to a friend. If just anyone just walked in your door to buy a boiler you would not sell it to him. I know the majority of the HVAC companies around here won't. Greg

Due to the closeness of the buildings in NYC, (row houses you call them flats I think) apartment buildings and the like, the neighbors might not like your boiler venting into their window with a side vent arrangement. That notwithstanding, unfortunately many building codes (and the bureaucrats that administer them) here are unable to adapt to new technology.

Tony

Just for fun i'll call my local plumbing supply as just a Joe off the street and get some numbers. Greg, they'll sell them to anyone who plunks cash on the counter. You can even buy complete boilers at my local Home Depot.

Well that is great, but it is not the same every where.

Greg

Most infloor radiant heat uses PEX these days, so no brown water, further you're describing closed systems, not open.

Actually, that _is_ the issue. You're asserting that the water heater loses more up the flue than does a purpose made boiler. I'm asking how much really goes up a flue when the exhaust gases are cool enough to go through a PVC pipe, as is the case for a modern high-efficiency water heater.

And what leads you to believe that I was referring to any other kind?

Who in NYC can afford a personal shop big enough to need its own heating system?

It may be "common sense" but heat pumps are one case where "common sense" goes out the window. The heat output of a properly designed heat pump working across a reasonable temperature differential is greater than the energy input via shaft work with the remainder being extracted from the environment. This is something one learns in any intro thermodynamics class. The difficulty is that the efficiency goes down if the temperature differential between hot and cold is too high, which is a problem in cold areas--using the ground water as the cold sink eliminates this problem.

Appears to be sufficient to back you into a corner from which you are forced to appeal to authority rather than supporting your argument with facts and figures.

The problem here is the cost of electricity compared to gas/oil. That multiple has to be less than the coefficient of performance. Gas has gone up significantly so those numbers are better now than ten years ago. The drilling/excavation for ground source loops and the expense of running a compressor year round are also considerations. A need for air conditioning helps the ground source case significantly.

This is true if you are using an electric heat pump--a heat pump can be powered by anything that can turn a shaft. One of my professors at Tech had a heat pump powered by a natural-gas fired engine--in addition to the heat pump it had a heat exchanger in the exhaust and another on the cooling jacket. Very efficient design, but expensive.

Ok.

Our rules specify minimum distances from windows, corners, eaves, opposing walls etc. but don't specify whether they are those of the owner or the neighbours. You don't want your boiler venting into your own windows either .

Mark Rand RTFM

Also not commercially practical right now. On another energy front, I'm still waiting for the decentralized generation/microturbine units to sprout all over the metropolis.

Well gosh - we all have that H2O stuff - just "unmake" it into 2H2 and O2 stuff and burn the 2H2 with the O2 and turn a turbine so you can 'make' 2(H2O).

What else do you want - hydrogen generation - free fuel and ..... ;-)

OBTW - Gloat :-) Had a new heat pump installed today. The last finally froze/locked/burned up. This one cost me $125.00 - Insurance is wonderful when it pays off! Two calls by a air conditioner guy - second day with a helper - cheap.

If you buy a previously owned home - consider buying insurance on the house elements. Seller paid 300 I paid 50 at the sale. My idea - (experience) - and it has paid off in aces.

I like the concept in general - great when you don't have gas. Running an air conditioner all of the time is expensive. Either you heat the outside or you cool the outside. My old one - likely this one also - maybe not... - ran as much without the fan running - simply to thaw out the inside or outside block.

When temps get close to freezing - the pump action isn't very good - can't chill something that is already cold - and not much heat is generated. Electric Heater coils are there - but the 60 amp breaker looks expensive to operate!

Martin

Martin Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH & Endowment Member NRA Second Amendment Task Force Charter Founder

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