Boiler Replacement

Big_Steve_2

I am about to embark on replacing my boiler heating system with the help of a plumbing contractor.  I currently have a 140,000 gas boiler (converted from oil) that dates from when the house was built in 1956.  The house is a 2200 square foot ranch that heats very well and is reasonably well insulated. 



I am leaning towards the Lochinvar Knight series boiler, wall mounted in the current furnace room and direct vented through the sidewall. 



My question is 1- Would I be wise to switch from zoning with circulators (currently have 3 pumps, and will be adding one new zone for indirect hot water) to zone valves



and 2-  Does anyone have and general comments about the lochinvar series of boilers?

Unit44

HVAC Service Technician

I have worked on several Knights and they are pretty good boiler i prefer the Buderus GB142 wall hung myself.  To answer your question zoning with circulators is fine but it will cost you more to operate with electric rates derating and such.  By switching to zone valves it will be cheaper to replace in the futrue if there is a failure.  What it all comes down to if i were looking at the job is, how big are the zones, is there infloor radiant heat on the zones, or are all the zones just baseboard or radiators.  If the zones are just baseboard or radiators and you are willing to spend the money then i would switch everything over to zone valves with one circulator for a drive pump problaby a Grundfos UPS15-58FC or a UPS26-99.

Big_Steve_2

another question

No in-floor zones, simply 2 zones of cast-iron baseboard and 1 zone of copper baseboard.  No zone is longer than 100' total right now, and they are all setup with "monoflow" type iron fittings.  All zones are driven by old BG series 100 pumps right now, can I just re-use one of those pumps to supply the water to the 3 new zone valves or will I need a substantially more powerful pump ?

CMadatMe

Change the Pumps

Personally I would make this a two temp system. I would have the boiler modulate to maintain a heating curve for the fin-tube and I would add some type of modulating mixing valve or injection pump for a secondary heating circuit for the cast iron. I would use a Grundfos Alpha to control my fin-tube zone and run another alpha as a system pump for my secondary heating curve for the cast iron while zoning that circuit off with zone valves.

Not familiar with the Knight don't see any around these parts. Best of luck

Big_Steve_2

Two Temp

What would the temps be in an ideal world for this system ?   I know that the knight will automatically increase the temp (180 ?) for domestic hot water, when that is called for, but what should the temp on the cast iron baseboard, and the copper baseboard be ?  I dont know if I will do the dual-temp option only because the copper fin-tube is in the basement area that is used infrequently. 



Another thing I thought of- I have an air handler in the house for summer A/C use.  Would I benefit at all by putting a hydronic heat coil in the return piping, and running that blower so I can pull the return water temperature down even more ?  It seems like the boiler would run more efficiently if I can pull that much more heat out of the return water. 

CMadatMe

Temps Are Dictated

By the heat loss, size of the heat emitters and their given output at different water temps depending on each zones flow rate. The better yet to have different water temps if you are going to keep that basement cooler.

Jean-David Beyer

depending on each zones flow rate

I suspect my contractor used Taco 007-IFCs in my system because it was a common pump size to use, and not really based on calculations. I have a mod|con boiler with outdoor reset, and I certainly get enough heat to heat my house. I calculate that the boiler is almost 100% oversized if running at maximum rate, which it never does (except when heating the indirect hot water heater). If it were not the smallest size in that product line, I would have selected the next smaller size. At minimum firing rate it can heat the radiant slab OK on warm days. On cold days, it fires more, sometimes nearly 1/2 the full firing rate.



The reason I think the circulators are oversized is because the temperature drops are very small -- upstairs, I get a few degrees drop (sometimes 1F or 2F, and always less that 10F) even on very cold days, and more often, only a couple of degrees.  Probably a Taco 005-IFC would be enough. Downstairs, the temperature drop can be more, because the area of the slab with the heat tubing in it is large compared to the fin-tube baseboard upstairs. These circulators are not so oversized as to make noise from excessive flow.



But I have thought about this a lot. Aside from the noise (that I do not experience), and the cost of running an oversized circulator, it seems to me that if I run a large enough circulator, I could get no measurable temperature drop through the heating loop. And it seems to me that that would not be a bad thing. Running that fast, I would get the maximum heat output for a given input temperature. The emitters would actually emit more uniform heat because the source end and the return end of an emitter would be at the same temperatures.



Now as far as condensing is concerned, it does not matter what causes the return water to be cool enough; putting hot water in and letting it cool down a lot in the emitters due to the flow rate (among other things), or putting it in fairly cool (but hot enough), and having it return at about the same temperature.



Am I missing something? In a modulating system, is there any benefit in getting 20F drops in fin-tube baseboard, or 10F drops in radiant slabs?

CMadatMe

What's Missing

Yes JD you are missing quite alot actually. I have a question. If my water temp entering is the same that is leaving where is the btu transfer coming from? Where is the energy that the emitter is sending out to the room come from?



Look at delta-t the opposite way air pressure in your car tires effects your cars fuel consumption. Will the car move if the tires have 20lbs of air in them even though they should have 30lbs? What effect does this have on your cars fuel consumption? Less miles per gallon right? It's the same thing in a heating system. The greater the delta-t the more btu's you can deliver at lower water temps and flow rates increasing your systems efficiency. This works best with convective type systems not radiant. With radiant we want a smaller delta-t to keep uniform heat transfer across a larger floor area when compare to a piece of baseboard.



You said your boiler is oversized.  Why not slow the energy you paid for down and use it instead of sending it back to the boiler to be reheated again? This will also help you condense more during the warmer winter months and days. Of course this is all dependent on the amount of baseboard you have.



As an example. A piece of Suntemp residential baseboard at 1gpm flow rate puts out an average of 550 btu's a ft on a 20 degree delta-t with 180 degree water. That same piece of board at 1gpm on a 30 degree delta-t will put out an average of about 440 btu's a ft. Can you overcome your heat loss with those existing emitters at 440 btu's a ft?



One of the suggestions I make to people that install or have mod/cons is to slowly change out existing residential board and put in high output board. While I would rather see panel rads in reality not everyone can afford it. So this is the next best solution. Take the above example of board and let's change it to high output..Here are the numbers.. On a 20 with 180 you get 800 at a 1gpm flow rate and on a 30 about 620 which is still more than residential. This is where I can even set a lower curve. Maybe even able to run a 165 supply 135 return on my design day. Now I'm in the condensing mode 99 percent of the heating season.



Here is the real sad issue.. There are far and few real hydronic heating designer/installing contractors but there are a hole heck of alot of plumbers, oil and gas companies. But as our industry changes, which I believe we are already in the process of ( just read the posts around here) the latter will be forced to be like the few or will be out of business.

Jean-David Beyer

Trying to understand this...

Sorry this got to be so long.



"I have a question. If my water temp entering is the same that is

leaving where is the btu transfer coming from? Where is the energy that

the emitter is sending out to the room come from?"



The water temperature loss, no matter what the flow rate, has to be a little more than zero. I just cannot measure a loss less than 1F. Is not the energy the emitter is sending out proportional to the difference between the temperature of the water in it and the air temperature outside of it? So with high (I assume you would say excessive) flow rate, the whole thing would be at essentially (though not exactly) the same temperature, like an electric baseboard. I have 14' of Slant/Fin Base/Line 2000 in each of my two rooms upstairs, even though the heat loss in those rooms is only about 3200 BTU/hr in each room at 0F outside. And here in New Jersey the tables indicate that 14F is the design day. So it does not take much. Now Slant/Fin say that if I put 110F water into these, I get 150 BTU/hr/ft at 1 gpm, and 160 BTU/hr/ft at 4 gpm. Now with 4 gpm, I assume I would get less temperature drop than at 1 gpm. It seems to me, what Slant/Fin are saying is that the greater the flow, the greater the heat output (though not excitingly greater), and of course, you would not want to go over 4 gpm for other reasons. If the flow is "too slow", I expect even less heat transfer because with very slow (laminar) flow, the interface between the water that is flowing and the copper tube would not be "scrubbed." And air bubbles would have to dissolve to be carried down to the air eliminator near the boiler.



When I ran John Siegenthaler's Series Baseboard Simulator on this, it says I can expect 2.7 gpm from a Taco 007-IFC in there (and 1.6 gpm with a Taco 003-IFC), and that I would get 6F drop over the 28' of Slant/Fin if I put 131F in. If I use the 003-IFC, I would get a drop of 10F, but would need 3 feet more Slant/Fin. And if I do not add some more Slant/Fin, I would need to raise the temperature to 134.5F.



Now in practice, I do not know what my flow rates are. I do know the water temperature sent by the boiler to the two zones, and the return temperatures. Since the temperature drops are considerably less than what J.S.'s program say, and since I trust his program, I must infer that my flow rates are higher than what he says. And that could be accounted for by the actual number of fittings, etc., in the walls and floor that I have not ripped up to see what they actually are.



"You said your boiler is oversized.  Why not slow the energy you paid

for down and use it instead of sending it back to the boiler to be

reheated again? This will also help you condense more during the warmer

winter months and days. Of course this is all dependent on the amount

of baseboard you have. "



I find this all very interesting. I do not have all the answers. As a non-professional, I imagine I have less answers than many of the participants here.



But consider what happens on a warm day when my boiler sends out 110F water and it returns at 108F or 109F to be reheated. It does not need to reheat much, and at around 110F I get some condensing anyway. Not as much as the radiant slab downstairs where it goes out between 70F and 107F (usually) of course. It needs to be reheated only a degree or two. In fact, the heat load upstairs is already so low that the modulating of the boiler usually drops out and it runs in bang-bang mode if only the upstairs is calling for heat. I could set the system up to put less than 110F into the upstairs, but the output from the baseboard under 110F is so low it just does not work very well. When I first started, I tried to put 80F water in there and not much happened. (I can change the reset curves for upstairs and downstairs independently, and at a push of some buttons, so experimenting is pretty easy. The big problem for testing is I cannot change the outdoor temperatures, so I am at the mercy of the weather, and it just has not gotten cold enough around here for proper testing at the low end.)



So it seems that if I put the slower pump in the upstairs circuit, I would need to either add a small amount of baseboard, or raise the supply temperature. Doing the latter would get me the same return temperature, and the same amount of condensing, or so it seems.





"As an example. A piece of Suntemp residential baseboard at 1gpm flow

rate puts out an average of 550 btu's a ft on a 20 degree delta-t with

180 degree water. That same piece of board at 1gpm on a 30 degree

delta-t will put out an average of about 440 btu's a ft. Can you

overcome your heat loss with those existing emitters at 440 btu's a ft?"



My existing emitters put out between 150 BTU/hr/ft with 110F water going in, and 275 BTU/hr/ft with 135F water going in. This with a 1 gpm flow rate. Slightly higher with 4 gpm flow rate. Slant/Fin do not mention the delta-T to be expected; they only say that the return air into the baseboard is assumed to be 65F. At 180F, they put out about 570 BTU/hr/ft. It appears I can easily overcome my heat loss with those existing emitters at 440 BTU/hr/ft. In fact, I can almost certainly do it at 275 BTU/hr/ft. That is the reason I had 14' of the stuff put in each room instead of the 3' that was in there before, which was clearly not enough (rarely could get the rooms over 62F). I wanted to run the baseboard zone at low enough temperatures to get condensing.



"This is where I can even set a lower curve. Maybe even able to run a

165 supply 135 return on my design day. Now I'm in the condensing mode

99 percent of the heating season."



I have enough baseboard so I run a maximum of 135F supply and I do not know what return when it is 6F outdoors. I run a minimum of 110F supply and about 108F return when it is 60F outdoors. Since my design day is 14F, I imagine I am condensing essentially all the time already. OTOH, if I am running at 130F supply and (guessing here) 125F return, it is condensing, but running only around 88% steady state boiler efficiency. Fortunately, the downstairs radiant slab zone is the part of the system that has the greatest heat loads, and runs at considerably lower temperatures.



"Here is the real sad issue.. There are far and few real hydronic

heating designer/installing contractors but there are a hole heck of

alot of plumbers, oil and gas companies. But as our industry changes,

which I believe we are already in the process of ( just read the posts

around here) the latter will be forced to be like the few or will be

out of business."



I agree wholeheartedly. The good part of my contractor is that they do not sell gas or oil, and they are good craftsmen. I am less certain of their ability to design things, though they do follow the installation manual rigorously. OTOH, they just walked around the outside of the house to compute heat loss, and suggested the next larger boiler, when my calculations indicated that even the smallest boiler in the line (W-M Ultra 3 80K) calculated to be a little too big. And running it indicates that if they made a 50K BTU/hr model, that would have been better. In fact, from the number of questions around her about using domestic hot water heaters to heat houses indicates to me that houses demand much less heat than they did 75 years ago (insulation, better windows, less leaks). And that, therefore, there should be mod|con boilers in smaller sizes than seem to be currently available.