New System...

ben01

Hello all.

I am in the planning stages of a full boiler replacement. My home was built in 1911 and is 3500 square foot above grade. The walls have been insulated with pour in place foam insulation and the entire roof line has been sprayed with 4" of closed cell foam, summer of 2015. Windows are original and will be replaced this summer. We have been here only this heating season.

Me, I am a Licensed Plumber in Illinois (Chicago burbs). Admiringly, I have very little experience with boilers. I will be replacing CI boiler from '66 and short cycles every fire. Most of the home has the existing Ci radiators which I will be keeping. The old gravity piping will be replaced with proper sized copper, in basement. Rooms such as family room and kitchen will be undergoing a renovation and I would like to use a underfloor heating system with supplemental base ray, depending on heat loss calculations.

Is anybody willing to point me in the right direction as far as products? I am strongly leaning toward a mod con but I'm worried about the low temps and the radiators.

Thanks in advance and any advice is appreciated!

Ben

Mark Eatherton

You came to the right place Ben.

First thing you need is an accurate heat loss calculation. Plenty of free programs on line from reputable companies.

That will basically dictate everything else that happens from there. Pipe size, boiler size, pumps, expansion tanks, everything. If you'll be keeping the beautiful high mass radiators, I'd recommend you install non electric thermostatic radiator valves (TRV's).

With all the conservation you've done, it shouldn't be a problem keeping the modcon in the sweet mode of condensing for better than 95% of the time the system is on.

Welcome to The Wall.

ME

Gordy

Save on the copper, and consider manifold home runs to your radiators. Use trvs on the radiators for total control.

Chester

CI radiators can be a perfect fit for modcons and low water temps.

Definitely start with a heat loss. Here's a way you can do it based on actual energy use using your existing boiler as a measuring device (credit to "Dana" who posts over at the terrylove forum):

1. Start with the amount of fuel used between two exact dates. Fuel use over a couple winter months is sufficient.

2. Download a daily "Base-65F" heating degree-days spreadsheet from a nearby weather station at degreedays.net and add up the HDD between the meter reading (or oil fill) dates.

3. Convert your fuel use (therms, gallons, etc.) to total BTU.

4. Multiply total BTU by a factor that represents the approximate real-world efficiency of your existing boiler (e.g. 0.85 -- although maybe lower for an older unit). The idea is to make an educated guess about the BTU the boiler delivered to the heating system versus the chimney. (You might be using some BTU for DHW, but that's usually a much lower percentage of total fuel use in the winter. You can either adjust for it or leave it alone and know that you're probably estimating your actual heat load on the high side.)

5. Divide that number (net-BTU used for heating over the measuring period) by the total HDD for that period. That will give you BTU per HDD.

6. Divide by 24, which is your BTU per degree-hour.

7. Find your 99% outdoor design temp: https://www.captiveaire.com/catalogcontent/fans/sup_mpu/doc/winter_summer_design_temps_us.pdf

8. Subtract your outdoor design temp (e.g. 2F for O'hare airport) from 65 (since you used Base 65 for HDD).

9. Multiply that number (i.e. 63, in this case) by the BTU/degree-hour you calculated in #6 above.

10. Voila! You now have an implied design day heat load of XX BTU/hr. Might not be perfect but probably close enough to determine what size boiler you need since boilers are sized in 'lumpy' increments. (When I did this it was within 10% of a Manual J.)

If you go with a modcon you can choose something big enough to comfortably meet your design day but that can modulate enough that it doesn't short cycle during warmer weather. For example, if your implied heat loss is 30,000 BTU/hr a nice fit could be a 60,000 BTU/hr modcon that modulates down to 10,000 BTU/hr.

Once you have a good heat loss calculation you can measure the EDR of your radiation to determine what water temp you'll need to cover your design day. Here's a chart you can use:

http://www.comfort-calc.net/userfiles/images/Heating Helper/CI_Radiation_Heat_Emission.png

That's a starting point for setting your ODR curve (probably way better than the factory default) and you can dial it in from there next winter.

Paul Pollets

The new Viessmann CU-3 works well with radiators and is a condensing boiler. Small footprint and easy to vent, wire and pipe.
http://www.viessmann.ca/en/residential/gas-boilers/condensing-boilers/vitocrossal-300-cu3a.html

ben01

Thanks for the replies! I will attempt the actual heat loss this weekend.

Can anybody recommend a good online heat loss calculator?

ben

Mark Eatherton

Slantfin seems to be a popular program. http://www.slantfin.com/homeowners-page/ipadapp.html

I wrote my own spreadsheet for doing the same thing, but with all of them, if you put garbage in, you get garbage out.

Don't guess at anything.

You also will want to do an EDR survey of your existing radiators. Once the load calcs are done, the square footage of the radiators will dictate the required supply water temperatures. If need be, you may have to purchase Dan's book titled Every Darn Radiator (EDR).

ME

Chester

Here's what I used to calculate EDR...

http://www.columbiaheatingsupply.com/page_images/Sizing Cast Iron Radiator Heating Capacity Guide.pdf

Rich_49

Careful with the centers and that guide . They can vary a bit .

ben01

Thank you, all! I have done a EDR calculation with a slightly more involved chart than was provided. The one I used focused on the the height, width, and number of tubes.

Also, to further complicate things there was an addtion put on the home in the early 80's which was forced air. Square footage is 557 up and 557 down for a total of 1114 square foot. In this area I want to use under floor tubing (in joist, to maintain even floor heights throughout.) complimented with base ray, depending on heat loss calculations.

The remainder of the home has cast radiators which i will be keeping, less the kitchen. Kitchen currently has 96 Sq ft of radiation and I would like to also use floor tubing.

The EDR calculation that i came up with was 782 square ft. The chart I used calls out for 185 btu's per square foot. That gives me a total of 144,670, not including the 1114 square foot addition.

With the charts supplied by Chester, the values are less and the BTU fugure is 170 per square foot.

I plan on completing the slant fin heat loss calculator tonight.

Thanks,
Ben

ben01

Ok, I completed a heat loss summary for the entire property. I completed it with the existing single pain windows which i currently have, although I intend on replacing them rather soon. A few (4) original stained glass windows will be staying.

To recap, I have a 3500 sq foot home which has entire roof line spray foam insulated and walls with a pour-able type of foam.

Heat loss calculations go as follows:

1st floor 68,015
2nd floor 30,555

Total: 98,570 BTU

Walk up attic shall remain unheated as its almost always 70 or near degrees, due to foam insulation.

Basement shall remain unheated and was factored in, during the heat loss summary.

Does 98K sound correct? Not that it matters, but my current boiler is a 220K but it was installed in 1966 before any energy upgrades were made.

Mark Eatherton

Looks close to reality to me. An industry "rule of thumb" is 30 BTU/Sq Ft/Hr, and you are right there. Now that you have a room load, do a reverse engineering on the EDR you have. Use the 170 number to see how oversized the radiation is.

ME

ben01

Thanks, Mark. I have radiators in all of the home, less the 1114 foot addition which is currently forced air.

Are you asking for reverse engineering for each room, which have radiators?

Mark Eatherton

Pick worst case scenario and cover that room and all the others will be fine. Worst case scenario would be that room with the highest loss per square foot of occupied space. Typically an outside corner with windows.

Calculation is fairly simple. Then you can do reverse engineering to see what kind of temperature you will need at design condition. The output of radiation is assumed to be fairly linear, so if it puts out 10,000 btuH At 180, and 0 btuH at 70, then you can calculate the required temperature based on your calculated load and design temperatures.

ME

ben01

Thanks. The living room has 2 outside walls, a 30 sq ft picture window and 3 other windows. its 21' X 14' and has an actual heat loos calculation of 10,799.

The EDR value at 170 degrees would be 18,700 BTU

Chester

Ben: did you end up using the Slant Fin calculator? Many reports I've read suggest it tends to come out on the conservative (high) side compared with a Manual J. That's certainly not a problem but your 98,000 may be toward the upper end of the 'realistic' range. It at least tells you that you don't need a 220K boiler! The question is whether you can get away with a 110 :-). Might use a different method just for comparison -- but it all depends how aggressive you want to get. In making my decision my risk tolerance was to aim for a boiler that was about 1.5 times heat loss with a lower end of about .5 times design day heat loss. as low as possible.

FWIW: The 'reverse engineered' EDR for my CI radiators suggested I could meet my design day heat loss with 130 degree water. In reality I've been able to dial it down well below that. I hit design conditions last night and the boiler was humming away at low-fire sending 108 degree water out to the system and the house is perfectly comfortable. My takeaway is that the radiation is way oversized (which is good) and the envelope upgrades I've done have been very effective. Huge difference in comfort and efficiency compared with the old on/off system at 180 degrees.

SWEI

I'd suggest looking for a minimum modulation rate that is one third or less of your design day heat loss. One quarter is even better.

Chester

Agreed. I think I meant to say .5 X average heat loss, not design day. Lower the better, of course.

ben01

Yes, I did use the Slant Fin program. I accounted for building conditions as they are today. I am planning some renovations this spring / summer which will include new windows and replacement of a few really bad doors.

In regards to the boiler, I once had my eye on the Navien NHB -150. It can be had for an incredible price, compared to the "name brand" boilers on the market. 150K BTU that has has a 15:1 turndown ratio. Does anyone have any input, good or bad on them? I have installed dozens of their domestic water tankless units with no real problems.

Is there a disadvantage to slightly over sizing a boiler with either a 150K or 199K, other than initial cost?

For as cheap as a tankless WH is, I am planning on installing one for domestic water and not going the indirect route.

Many thanks!
Ben

nicholas bonham-carter

If that Navien is a hot water heater, it will not provide enough flow for your heating needs, so back to the drawing board.
Heating boilers are more expensive because they are able to provide enough hot water flowing through to heat the house.
Instant hot water heaters are quite different. --NBC

ben01

Nope, the Navien NHB - 150 is actually a 10K to 150K boiler.

http://us.navien.com/Product/Page1/Details/NHB-150?Category=NHB series

Rich_49

Tankless and a 15:1 boiler huh ? Don't take this the wrong way Ben , revisit your choices . That's 2 gas lines , 2 flues , 3 xs the BTUh you require to do both operations , twice the wiring for power . You're really saving money now , and all for a system that you will hate in short order .

Put your plumber pants on and get busy thinking this thing through . You are in the right place to ask questions and get some advice . Based on your heat loss and the suggestion of a tankless and boiler I offer the following recommendation .

HTP Versa Flame or HTP EFTC140W . Should not break your heart to spend less money , buy American and get better performance on both operations .

http://www.htproducts.com/versaflame.html

http://www.htproducts.com/EFT_Combination_Floor.html

Maybe someone else will chime in on your choice also .

SWEI

ben01 said:

Yes, I did use the Slant Fin program. I accounted for building conditions as they are today.

Probably 30% headroom in that number. Call it 20% to be safe.

I am planning some renovations this spring / summer which will include new windows and replacement of a few really bad doors.

You really need to run the numbers on the improved envelope as well. Size for the lower heat loss and make it up for a year with electric space heaters if you have to.

hot_rod

ben01 said:

Nope, the Navien NHB - 150 is actually a 10K to 150K boiler.

http://us.navien.com/Product/Page1/Details/NHB-150?Category=NHB series

If it is a Combi unit you need that high BTU to provide adequate DHW production. For a boiler dedicated to heating there are a number of brands that modulate down to 8,000 BTU/ hr in 7-1 turndown versions.

ben01

I am not committed to installing the Navien... This unit offers quite a bit for well under 2K in cost, that is what attracts me to it. In regards to the domestic hot, I was thinking the alternate tankless heater as opposed to an indirect unit, based on piping and tank costs alone.

I suppose with the load calculations I have arrived with, I could also get away with a combi unit. Many combi units have 120K and up on the heating side.

With regards to installing the smallest boiler possible, based on my anticipated heat loss (after new windows and doors), is there a major disadvantage to having a slightly larger heating boiler than needed? lets say 20 - 40 K over, on a mod con?

The HTP combi I am not familiar with, can any others chime in on this unit?

Thanks
Ben

bmwpowere36m3

As with any boiler, if you oversize you lose efficiency, especially in the shoulder months... like 75% of the season. However certain mod-cons with large turndown ratios, it's less of an issue due to minimum fire rate.

Re-run the heat loss calcs at 50* ODT and see how that matches up with the minimum fire rate of the boilers your considering.

hot_rod

120,000 is a bit small for a combi unit to provide adequate DHW in winter months when the incoming water is coldest. At least from my experience, and we are a family of two. If I have some sunny days the solar pre-heat tank will make it all workable, but a week without any solar, no go, you might get a luke warm shower.

But a 120, even an 85 would easily drive a indirect, as you have some storage in the bank. It kicks on to high fire, drops the heating load and recovers the DHW quickly.

But pay attention to your actual required DHW load, in many cases with small efficient homes the DHW may be the larger load. Any boiler under 80K input may not be adequate for a family with large DHW expectations. It could spend a fair amount of time in DHW priority, if all the DHW hits in the late afternoon evening hours, like bathing, dishwasher, clothes washer, etc.

I'm looking at the Lochinvar KHN085 for my next upgrade.
8.5- 85,000 input, nice control features, etc. Lochinvar still uses that tall fire tube HX, others have gone to a stubbier Korean built FT design with multi metals. I'm not a fan of aluminum in the flue gas path.

All the major boiler brands have good offerings, many installers shop by the support and availability as much as the name on the front.

Gordy

The khn is impressive. Well written manual. Also no question on what the min max flow rates are at what fire. They tell you.

ben01

Hot Rod - I was referring to combi units which have 199K for the domestic hot and 120K for the heating side.

With a actual heat load under 100K I would think a unit of this size would be adequate, would you guys?

Thanks
Ben

Gordy

Quite frankly if budget is for a cheap brand HE combi I would recommend a right size ci boiler, and an indirect. Done.

ben01

Honestly, budget is not necessarily a huge concern. Due to the heat load calculations, I should be able to use several mod cons on the market, correct. Weather it be a Triangle Tube, Lochinvar, or other brand out there.

Putting cost aside, would I be better suited for a boiler with an indirect WH?

I would like to have a combination of my existing radiators along with under sub-floor heating and base ray where to be sure heat loads are meet in certain rooms.

Thanks

ben01

Hatterasguy said:

ben01 said:

Putting cost aside, would I be better suited for a boiler with an indirect WH?

Putting cost aside, EVERYBODY would be better suited with a boiler and an indirect WH.

The compromise of a combi was developed for the cheap and the ignorant. The combi excels at doing nothing well. It can work in certain circumstances but it is never ideal.

Thank you, that's what I am looking for!

With that said, are there any recommendations on how to size a boiler with the heat loss calculations I have and a indirect WH?

Thanks

ben01

Thanks. I am not too familiar with Lochinvar, is this the model you are referring to?

http://www.supplyhouse.com/Lochinvar-WHN-110-89000-BTU-Output-Knight-High-Efficiency-Boiler-w-Fire-Tube-Heat-Exchanger-Wall-Mount

As far as the indirect sizing, I would be inclined to increase the sizing as we have a family of 5 and typically have a consecutive shower pattern.

Ideally, with a mod con, you would still want lower temps with the indirect, right? If so, will the lower temperatures need to be accounted for when sizing the tank?

What's the best way to regulate temperatures between zones? (floor tubing, indirect, 1st floor cast radiators, and 2nd floor cast radiators)

Thank you
Ben

hot_rod

I would suggest a 50 or 60 gallon indirect, with your family size. It's rare that someone complains about too much DHW in their home.

The boiler will go to high fire, high temperature when DHW calls. So the tank will recover via the full output of the boiler, which will be about 3 times what a typical gas fired tank type WH would have, they are usually in the 30- 40,000 input at maybe 80% efficiencies. I believe you can adjust the temperature that the boiler runs up to for DHW. you could experiment and see how low you could set that and still provide adequate DHW. Use an indirect with plenty of surface area to play low temperature games. The Lochinvar Squire has a large diameter, smooth, stainless hx, might be worth a look.

http://www.lochinvar.com/_linefiles/SIT-02.pdf


The boiler has the ability to run outdoor reset as well as multiple temperatures. You will need a mixing device that connects to the boiler to implement the controls ability to provide multiple temperatures.

The boiler is set to the supply needed by the high temperature zone on design day, the mixed temperature also.

The boiler has near infinite adjustability, and a good company behind it.

ben01

Looks like a great unit!

So, each zone temperature shall be regulated through a standard mixing valve? If CI radiator zone temp was to be be increased or decreased (by user), mixing valve(s) would then need adjustments too?

Without the need for primary / secondary piping does anyone know if there is a schematic out there to view? I looked through Lochinvar's web site but found nothing. There seems to be little info in this boiler, perhaps as it's fairly new.

With regards to floor tubing, my kitchen and family room (open concept 875 square foot) have a current heat loss calculation of 39,358. Even when envelope repair are made to this area, I believe I will still need supplemental heat (base ray) to properly cover heat loss. This area currently has forced air which is gone once remodeling begins, in spring.

Are there any recommendations on transfer plates? I will be going through 3/4 tongue and groove plywood and 3/4" hardwood oak on top of that. All of the outer rim joists in the basement are already sealed with 2" foam board and buttoned up with great stuff insulation and has r-13 Roxul on top of that.

Thanks
Ben

Mark Eatherton

As for DHW production, I'd rather spec a "reverse indirect", which might cost more initially, but will work in the condensing range of the heat source, keeping the heat source as efficient as possible, while providing copious amounts of hot water. As has been mentioned, if all of your DHW loads are short in duration, but in series use pattern wise, you may not even need a tank. A good flat plate heat exchanger will be capable of transferring the full output capacity of the boiler to the DHW load.

What dictates storage tank size is parallel loads or a "dump load". If you have a wife like mine, she is not willing to wait at 2 GPM to fill a 40 gallon tub, when she could fill it in 5 or 10 minutes, depending. THAT is where the dump load must be taken into consideration. When I had a tankless, I taught her to start filling her tub at a real low flow rate (high delta) right when the news started on TV, then when the weather started, she'd run in and shut it off, and have a nice full tub of really hot water to bathe in. Not everyone is willing to do that for the sake of efficiency... Not everyone is willing to pay the going price of a Reverse Indirect either. It is essentially a large tank with a LOT of copper heat exchanger inside it to allow excellent heat transfer. It typically requires an approach temperature from the heat source that is only 10 degrees F hotter than the desired potable water temp. (140 tank set point for 130 F water for example). You still have to provide an ASSE 1017 valve to avoid the possibility of scalding occurring. Google TurboMax for more information.

I live in a house that is 1955 vintage 2,206 sq. ft. living space home (capable of delivering 20 btu's/sq ft//hour). It has new dbl pane windows and blown cellulose in the walls. It is carried by a 50K btuH modcon Munchkin, with an 80 gallon reverse indirect, and we NEVER run out of hot water, but we also only run one load at a time. And I've never been uncomfortable.

Loss calc said I needed 40 btu's/sq foot per hour... I wouldn't suggest that ANY contractor stick their necks this far out on the line, but I did in my own home (experiment) and it works fantastic.

Bigger is not better, if appropriately sized. Mass and momentum have a lot to do with it that are NOT taken into consideration in ANY Load calc I am familiar with.

ME

Chester

One reason I like the idea of using weather-adjusted historic fuel use to estimate heat loss is because it accounts for a variety of site-specific system and envelope characteristics that aren't captured with the Slantfin or other similar approaches. The major variable is adjusting for the estimated real-world efficiency of the existing boiler and how many BTUs are used for heat vs. DHW.

But one of the biggest things I noticed with my new modcon (especially now that we've finally had some design day temps) is the 'comfort' factor where the radiators just stay warm all the time and the walls, floors and furniture stay at a pretty constant temp. I think comfort and efficiency go hand in hand.

I assume that's what you mean by mass and momentum? The analogy being that it takes much less energy to keep a car at a steady state speed compared with lots of acceleration and deceleration?

I think I read that the Slantfin program is based on an I.B.R. concept that assumes you have to heat up all the piping and radiation mass before you get any usable heat. That's obviously not relevant when you have a system that runs more or less at steady state conditions.

Mark Eatherton

Chester said:

One reason I like the idea of using weather-adjusted historic fuel use to estimate heat loss is because it accounts for a variety of site-specific system and envelope characteristics that aren't captured with the Slantfin or other similar approaches. The major variable is adjusting for the estimated real-world efficiency of the existing boiler and how many BTUs are used for heat vs. DHW.

But one of the biggest things I noticed with my new modcon (especially now that we've finally had some design day temps) is the 'comfort' factor where the radiators just stay warm all the time and the walls, floors and furniture stay at a pretty constant temp. I think comfort and efficiency go hand in hand.

I assume that's what you mean by mass and momentum? The analogy being that it takes much less energy to keep a car at a steady state speed compared with lots of acceleration and deceleration?

I think I read that the Slantfin program is based on an I.B.R. concept that assumes you have to heat up all the piping and radiation mass before you get any usable heat. That's obviously not relevant when you have a system that runs more or less at steady state conditions.

Your assumptions are correct Chet. What I don't like about using typical average fuel use is that unless you have a LOT of relevant site data, that is an average of averages, and doesn't break it down to an hourly accurate picture. Due diligence requires us to perform an actual load calc., but as has been stated numerous time, GI=GO. Hopefully some day in the distant future,we can roll the mass characteristics and solar gain characteristics into the picture to fine tune our offerings. In the mean time, we have controls to do that for us. But yes, you are correct that that is the influence of mass over reality. It can also work against us, if allowed to.

Great conversation.

ME

hot_rod

ben01 said:

Looks like a great unit!

So, each zone temperature shall be regulated through a standard mixing valve? If CI radiator zone temp was to be be increased or decreased (by user), mixing valve(s) would then need adjustments too?

Without the need for primary / secondary piping does anyone know if there is a schematic out there to view? I looked through Lochinvar's web site but found nothing. There seems to be little info in this boiler, perhaps as it's fairly new.

With regards to floor tubing, my kitchen and family room (open concept 875 square foot) have a current heat loss calculation of 39,358. Even when envelope repair are made to this area, I believe I will still need supplemental heat (base ray) to properly cover heat loss. This area currently has forced air which is gone once remodeling begins, in spring.

Are there any recommendations on transfer plates? I will be going through 3/4 tongue and groove plywood and 3/4" hardwood oak on top of that. All of the outer rim joists in the basement are already sealed with 2" foam board and buttoned up with great stuff insulation and has r-13 Roxul on top of that.

Thanks
Ben

Size the heat emitters to try and work with one or two temperatures. No need to have a bunch of mixing devices if you can keep supply temperature requirements within 10- 12° of one another, KISS.

Maybe hire one of the designers here that have experience playing with temperature and heat emitter sizing. Tube spacing panel rad types all can be selected to simplify the piping and controls.

The plates from Radiant Engineering www.radiantengineering.com are the best in my experience. The tube grip is critical for the heat transfer as well as eliminating the tube movement noise.
Extruded plates contact the subfloor best, and the heavier gauge aluminum moves the heat to the outer edges best. I believe most of the radiant manufacturers sell the RE plates, if they are extruded versions.
That 875 space may be a tough go with just radiant floors, this is where a qualified designer can keep you out of trouble. note the number of under-heating posts this week.=y

Jason_13

Let's re-look at the heat loss. I feel you are still off with foam insulation. Also include all your other upgrades now to maximize your fuel savings and buy even a smaller boiler now.
I also like the idea of an indirect which is well insulated and minimal standby loss. Less fuel to heat still water than moving water.
Lastly I like the Burnham alpine with the new Sage 2.2 control. Turn down the input to match the heat loss and match the tank requirement so you never input more than you need. Increase the savings with the new Sage Zone Control which you can program per zone and it reduced the input to match the maximum input per zone or minimum input if the input is less than the minimum input of the boiler. You can actually input to 100 btu's. Can any boiler go that low? No but will stay at minimum until the total btu's of demanding zones exceeds the minimum input of the boiler is exceeded.
Maybe the next version they will allow "0" btu input just to start the pump on a really small zone and fire when a larger zone calls or time out and fire in case a larger zone does not fire.

Chester

"... doesn't break it down to an hourly accurate picture. Due diligence requires us to perform an actual load calc."

ME: Just curious why you need hourly. And I'd argue that historic is an actual load calc, just a different way of doing it.

I can see that if you're designing a new system you need much more granularity -- room by room, etc. But if you're just going to drop in a new boiler I'd think all you need out of a heat loss calc is to make sure that a) you can heat the place at design conditions AND b) you can fire low enough to manage off-peak loads for your smallest zone.

Glad you think it's a good conversation. Let's take it over to a fresh thread...and have a contest!