Undersized boiler

NealFoley

We've been in our house for a year and have been trying to improve the heating and reduce the cost.

Last spring we did a major air sealing and insulation project on the second floor of the cape section of the house.

We've also insulated all the Pex to the baseboard we could. Some of it was just laying on the ground in an unheated crawlspace..... Not ideal for Maine in winter. I think the heating contractor was relying on glycol a bit too much....

When we first moved in we I turned off the outdoor reset because it was taking all day to bring the house from 56 deg to 60. Running the baseboard at 180 solved that. But this year with the extra insulation in attic and on pipes I decided to try outdoor reset again.

But it's tracking--thanks to Nest data-- More than twice as long too heat from 56 to 62. And it isn't even that cold.

I just did a heat loss calc and I think it's about 44000btu/hr.
In doing so I also checked on the required boiler size for this house--128,000.

6 years ago the previous owner had a new propane boiler and the baseboard installed. The boiler is an NTI trinity 85. Used for radiant heat and dhw.

Any creative ideas on how I can make this boiler operate more better given it's a bit small for the house?. We have one whole section turned down and all but sealed off but the rest of the house is quite cool.

We're continuing to improve insulation as best as we can. But the crawl space is uninsulated and tight.

A future upgrade--before replacing the boiler--is to replace the baseboard with flat panel radiators which are correctly sized for each room.

Rich_49

Can you explain how you figured the heat loss at 44,000 BTUh ?

Why do you believe that a 44,000 house requires a 128,000 BTUh boiler ?

You need to or have someone qualified perform a room by room heat loss and also measure the installed baseboard element in each room . The ODR curve then needs to be fine tuned taking all that is connected into consideration .

Check to make sure that the ODR sensor is on a North wall in a position where it is never exposed to sunlight .

The Trinity is quite possibly large enough for the home but may not be set up , piped , controlled properly or advantageously .

Where in Maine are you , maybe we know of someone capble near you to assist ?

Ironman

Agree. A house that has a 44k btu load only needs a boiler and system that can deliver that much heat. If you really needed a 128k btu boiler with only a 44k btu load, then your system would only be 34% efficient. In other words, you would be wasting 66% of the heat produced by the boiler.

Also, a hydronic system on ODR works best with the thermostat left alone on one constant temp. Setting it back and then up is actually counter-productive to the logic of a mod/con boiler. Setback is old school technology for non modulating equipment. The Nest is for the birds!

NY_Rob

If your heatloss is 44K BTU's that means your boiler and radiators need to put out 44K BTU's to offset heatloss.

What is the square footage of heated space in your home?
Fin-tube baseboard or cast iron baseboard?

Please measure the length of fin-tube inside your baseboard.
The baseboard enclosures could be 10' long but it may only contain 7' of actual fin-tube. If you add up all your fin-tube, it's easy to calculate how many BTU's your baseboard is capable of radiating.

Slant-fin has an app to help you calculate heatloss, it's usually overestimates heatloss, but it will give you a ballpark heatloss figure to work with.

NealFoley

After doing some research I used a heat loss calc to achieve the 44000 but/hr rate. I also did a real time heat loss and got 51k.

The house is 2525sq ft. So I used the common multiplier of 50btu/sq ft to achieve the 126k boiler figure.

The house is an 1770s cape with an 1820s addition. Apart from the insulating we did in the roof and attic--R38--the insulation is from the 50s. A mix of r13 rock wool and vermiculite fill which has settled . The floors are uninsulated.

The ODR is on a shaded north eave.
We are near Rockland Maine. The area's biggest heating contractor installed the system . As a former contractor I have not been impressed with their answers to our questions about the system, nor the quality of work and the fact that unsolicited they sent us a bill for a maintenance connect we never asked for.

NY_Rob

50K BTU's/Ft heatloss is for an open garage in Alaska, most "modern" nominally insulated 2x4 built homes in the US are in the 15-20BTU/sqFt heatloss range.

There are pros here who have been doing this for many years and have stated on many occasions that they have never seen a home with heatloss at or over 30BTU's/SqFt.

If your heatloss is very high at 25BTU's/SqFt that would give you 62K BTU's heatloss on the coldest day of the year.

You have plenty of boiler for your house.

NY_Rob

A couple of things to keep in mind with the type of boiler you have- a modulating condensing boiler.

They are designed to be efficient using low temperature water for heating. Your old system was designed to supply 180F water to your radiators, and your radiators were sized based on 180F supply water temperature not 120F-140F supply temps.

If your home has say 50K BTU heatloss, with 180F supply water (170F Average Water Temp) you need 98ft of fin-tube to keep up with heatloss.
Now suppose the new boiler is supplying 140F supply water (130F AWT), you'll need 192ft of fin-tube to keep up with heatloss.

To remedy the above situation, you can either raise the boiler supply temperature, you can add additional radiation... or a little of both. Luckily, most homes have more radiation than needed, so you usually can get away with lower supply temps, but you can't go straight from 180F supply temps to 120F supply temps without adding extra radiation, adding insulation, reversing flows, etc...

Also, you should not be using deep setbacks with mod-con boilers. 1-2deg may be okay, but 4/5/6deg setbacks will take hours to recover and your savings go right out the window at that point.

Big Ed_4

I would be looking at the radiation in your home and delivery piping .. I never was an big fan of baseboard . It's high temperature convection heating taking up wall space . Furniture , drapes , dust and thick rugs blocking air movement through the baseboard could one reason the heat can not catch up to the heat loss . This is an normal service call in the cold of winter, not how much you have but how much you see.... Normaly installed in series , given up BTU's along the way .. Too much installed on the loop, the end will deliver zilch ... Too long and too small of the piping will add resistance effecting the flow and output .. And of course not enough baseboard would affect the BTU replacement ..

An condensing boiler is not the right choice for baseboard ... Yes panel radiators and radiant , then you will get those sexy efficacy ratings ... Running one at high temperature will just eat away at it's 20 year life

NealFoley

NY_Rob said:

If your heatloss is 44K BTU's that means your boiler and radiators need to put out 44K BTU's to offset heatloss.

What is the square footage of heated space in your home?
Fin-tube baseboard or cast iron baseboard?

Please measure the length of fin-tube inside your baseboard.
The baseboard enclosures could be 10' long but it may only contain 7' of actual fin-tube. If you add up all your fin-tube, it's easy to calculate hoe many BTU's your baseboard is capable of radiating.

We've got 126ft of actual fin tube. I can't find a brand. The fins are 2" square on 3/4" pipe.

I've never been a fan of baseboard radiators. I much prefer panel radiators which is why we'll be switching. They worked fantastic in my last home where I designed and built a gasification boiler system with them for an old farmhouse.

NealFoley

NY_Rob said:

A couple of things to keep in mind with the type of boiler you have- a modulating condensing boiler.

They are designed to be efficient using low temperature water for heating. Your old system was designed to supply 180F water to your radiators, and your radiators were sized based on 180F supply water temperature not 120F-140F supply temps.

If your home has say 50K BTU heatloss, with 180F supply water (170F Average Water Temp) you need 98ft of fin-tube to keep up with heatloss.
Now suppose the new boiler is supplying 140F supply water (130F AWT), you'll need 192ft of fin-tube to keep up with heatloss.
.......
Also, you should not be using deep setbacks with mod-con boilers. 1-2deg may be okay, but 4/5/6deg setbacks will take hours to recover and your savings go right out the window at that point.

The radiators were installed at the same time as the boiler.... Again, I'm not impressed with the contractor who did the job..... They sold the owner a mess. And when she complained that the house was never warm they sold her a couple of wall heaters instead of trying to troubleshoot a badly designed, poorly installed system.....

Initially when we put in the Nest it helped us save propane in a big way. We were shooting through 2-3% a day. Now we're trying to fine tune usage.

When I turned off ODR last year it was precisely because of the design temp of the baseboards..... The system responds quicker and the rooms feel warmer at 180deg supply.

I decided to revisit it this year to see if it might make a difference. The only thing I can see is that it's taking longer to achieve the target which is certainly using more electricity, if not more propane due to a longer run time.

The decision to use a Nest for the main downstairs loop was to regulate the temperature when we're not home or using that part of the house. It seems to be saving propane/electricity use. Am I wrong in this assumption with a Mod/Con?

There are four zones in the system, each with a thermostatically controlled pump. Two of the zones we have turned down to a minimum. One because we are rarely there. The other--the kitchen--, because despite getting some insulation on the pipes, they still run through an unheated crawlspace and most sit on the frozen ground. The water goes out hot, but comes back ice cold.

The two other zones are our main living spaces. One has the Nest, the other a programable thermostat.

NY_Rob

126' of fin-tube at 510 BTU's/ft with 180F supply water (170F AWT) gives you the capacity to radiate 64K BTU's.

126' of fin-tube at 260 BTU's/ft with 140F supply water (130F AWT) gives you the capacity to radiate 32.7K BTU's.

It's easy to see why you're not getting enough heat.

Not much you can do about it during heating season other than raise the boiler supply temps and ditch the setbacks so there's no long recovery period.

FWIW- High mass cast iron baseboard (Burnham BaseRay, Gov-Board) works great with mod-cons if you have room to add more radiation.

NealFoley

Thanks for all the great information!

So let me get this straight... It's better/ more efficient with a Mod/Con to allow the boiler just to run at 180F with the thermostat set at, say, 62F and let it keep it there, then it is to fluctuate between 56 and 62 twice a day...? We are out most of the day 7 days a week..... It just seems counterintuitive to heat house at times when were not using it.
It's confusing without an easy way to track energy use vs propane consumption other than tracking the dial meter on the tanks.

NY_Rob

FYI.....

Ironman

NealFoley said:

Thanks for all the great information!

So let me get this straight... It's better/ more efficient with a Mod/Con to allow the boiler just to run at 180F with the thermostat set at, say, 62F and let it keep it there, then it is to fluctuate between 56 and 62 twice a day...? We are out most of the day 7 days a week..... It just seems counterintuitive to heat house at times when were not using it.
It's confusing without an easy way to track energy use vs propane consumption other than tracking the dial meter on the tanks.

What's your missing is that the boiler modulates it's firing rate from 20-100% depending upon the demand placed upon it. You appear to still be thinking in terms of a standard boiler which always fires at 100%.

The ODR feature also varies the water temp supplied by the boiler. The lower the water temp, the more efficient the boiler is. If your baseboards need 180* SWT when it's 0* outside, they will only need 140* SWT when it's 35* outside. The baseboards output is about 1/2 with 140* SWT, and the load on the house is 1/2 at 35* OAT.

Ideally, the most efficient operation of a mod/con would be for it to fire at its minimum for as long as possible with as low of a water as is just necessary to heat the structure.

Look at the charts that NY_Rob posted.

NY_Rob

For illustration of the role the Outdoor Reset Sensor plays in determining the temperature of the water the boiler supplies to your radiators, below is the ODR curve I currently use with my 80K BTU mod-con boiler with fin-tube baseboard.




If you notice, I never use 180F water- I only go up to 150F if it's -1F outside.

On a typical day at 32F outdoors my boiler is supplying 124 deg water to my radiators. It's common to use supply water temp -10F to come up with AWT (Average Water Temp) and use that figure for BTU output.

My ODR curve is somewhat typical but not completely ideal. I'm limited on the low end by the length of my shortest fin-tube zones and my boiler's minimum fire rate of 8K BTU's.

NealFoley

Ok. I get it. The chart and the list help clarify things a lot. I don't need to turn off ODR... I need to set the thermostats and leave it alone......

MikeG

In the first post glycol it was mentioned, that will reduce heat transfer along with a host of other possible issues. i have to believe there is a way to add more insulation to the crawlspace walls to prevent frozen ground, insulate the floors, and add more insulation to the tubing through the crawl. Can the tubing through he crawl instead of laying on the ground if that is the case be run up closer to the floor and insulated.

Ironman

The Nest is a problem. It will always be trying to set itself back and up based upon your life style. The Nest doesn't play well with modulating equipment.

If you want a wifi connected stat, get the Honeywell Lyric. It won't be spying on you either.

NY_Rob

Re the ODR curve, perhaps go back to factory default and see how that works out.

The factory default curves are like the old computer BIOS "Fail Safe" settings- they're not efficient but they will get you up and running and you can tweak/fine-tune from there for efficiency.

NealFoley

NY_Rob said:

Re the ODR curve, perhaps go back to factory default and see how that works out.

The factory default curves are like the old computer BIOS "Fail Safe" settings- they're not efficient but they will get you up and running and you can tweak/fine-tune from there for efficiency.

I've set it like this:

Ironman

That's a good start. I'd stretch the "maximum outdoor" to 68*.

NealFoley

MikeG said:

In the first post glycol it was mentioned, that will reduce heat transfer along with a host of other possible issues. i have to believe there is a way to add more insulation to the crawlspace walls to prevent frozen ground, insulate the floors, and add more insulation to the tubing through the crawl. Can the tubing through he crawl instead of laying on the ground if that is the case be run up closer to the floor and insulated.

I dislike glycol because it lowers efficiency. But in this case I think it has to stay. The installer should have run an insulted underground style Pex line through the crawl space where they couldn't get anyone. At the very least. I may have to tear out what's there and do this myself. The round about way the lines are run now makes it almost impossible to neatly tuck them up to the floor. Some places in the crawl space are only 10" been dirt and joists.

A remodel just before we bought the house corks have addressed all of this as the kitchen and bathroom floors were torn up. But I guess the owner and the contractor didn't deem saving money or the heating system necessary. I've been a little peeved to find debris from the remodel thrown down on top of the Pex tubes in places.

Insulating will continue as time and money allow. I plan on crawling around under the house with a foam pack at some point so I can insulate the sills and exposed stone walls and to add more insulation to the Pex wherever I can. As it is, this week I need to get under the bathroom to create a foamular box around all the plumbing.... The contractor thought it was a smart idea to rely on a small space heater set on a thermostat to keep the pipes from freezing. It didn't work last winter very well..... I figure enclosing the space just under the bathroom will at least make the heat more effective and help take the strain of the bathroom radiator. It will be a few years before my part time efforts will get me enough height to work on an proper solution.

Big Ed_4

You have 128+- feet of base board on zone ... It would not work .. It's the minimum for two zones , on 3/4" copper . Crimped pex ??. Maybe I missed something . Three zones ?

Big Ed_4

Homerun system piped reverse return...... I would recomend 3/8" risers lines, for flow and ease of running . Tuck them and run them along the floor boards back to the boiler .. .. Anyone know where to order 3/8" A pex manifolds ??.. Use Panel radiators with throttling TRV's ... Over size the panels a bit , make it look proportional to the space .. Then run it on the ODR. The system would run nearly constant .

mikeg2015

You might also check flow rate. Too low of flow rate and you lose capacity. Too high and the condensing boiler might be limited due to high return water temp. Just another variable.

NealFoley

Big Ed said:

You have 128+- feet of base board on zone ... It would not work .. It's the minimum for two zones , on 3/4" copper . Crimped pex ??. Maybe I missed something . Three zones ?

There are three zones controlled by thermostat controlled pumps. One of those is broken into a fourth zone by zone valves to a fourth thermostat. The two smallest zones are the two upstairs runs. The biggest zone is in the closest part of the house.

NealFoley

mikeg2015 said:

You might also check flow rate. Too low of flow rate and you lose capacity. Too high and the condensing boiler might be limited due to high return water temp. Just another variable.

I've been wondering about flow rate. Unfortunately there isn't much info I can go on. The system has almost no gauges. The pumps are Taco 007 F5s. So the rate could be anything.

The boiler requires a minimum of 3.5 gpm. I prefer alpha pumps cause you have some control and a readout.

From the screen it appears the water returning is within 5 degrese or so lower than outgoing once the system has fired.

I suppose one could limit the flow by cracking a valve closed a bit. But that's a risky, short term solution.

Paul48

I'd run the boiler as a bang-bang boiler for this heating season. The ODR will not work well with the thrown-in system. Next spring, add radiation to get your design-day supply temps down to 140-150*. Balance your zones, so they are close in required btus. Get those PEX lines up off the ground. The boiler will attempt to heat the ground.
Regarding setbacks and mod/cons..........Everything in the house becomes an emitter. The furniture, the walls, everything provides information to the mod/con running on ODR. If you set back and let all that material get cold, when you come out of setback, the boiler will supply just enough heat to overcome the outdoor cold. It will take forever for everything to warm up again.

MikeG

I feel your pain on the low crawl space. I have an old farmhouse with hewn log beams. I had to tunnel under some of them to get to parts of my crawl space. I originally installed fiberglass under the floor thirty some years ago and extruded foam along the inside block. I have since gone under and removed the fiberglass, more fun the second time and cut 2" extruded foam to fit tight to the floor, insulated the rim beam with foam board and spray foam. I also boxed in under the bath room tub and drain to keep that warmer. It never freezes under there. I have very little heating tubing under the floor except in the newer addition. That has a higher crawl and the pipes are insulated and run tight to the floor joists. The old part of the house has finned BB pretty much around the whole perimeter except where it had to run under the floor to get past an entry door. A lot of work and I have to psych myself up to go work under there.

HomerJSmith

Oy! Where to start. Good Comments. The best place to start is, I guess, at the beginning.

Neal, you want lower operating costs at your preferred comfort zone. Also, you have fixed systems, both heating and house design. You want to know what to do to achieve your goal.

I think this post got off on a tangent on baseboard (BB) although that is very important. My thoughts on BB. I have Fineline 30 E-75 in my home and switched from a SlantFin cast iron boiler to a mod com boiler and it works fine. However, as Big Ed said, it ain't a perfect fit. Mod Con is more suitable for in-floor or panel radiators. Neal, can you add panel radiators, increase your heat emitters?

NY_Rob, I have always over designed my BB. 1gal/min at 180 deg at an output of 450 BTU's per linear foot. The manufacturer test under the ideal conditions. Lint, carpet fibers, hair and dust build up and affect the output after time. Usually, BB is installed in series which diminishes the radiation output from the last BB.

Neal, I don't know how your system was designed. AT 3.5 gal/min minimum the pressure loss thru the boiler is low.
You have four zones each run by a Taco 007as I understand. I understand that some mod com boilers can be run on
a primary system. I only believe in a primary secondary system.
I would configure your system as follows: I have always thought of the heat source as the primary system and the distribution system as the secondary system, other have reversed that concept. First: The boiler has a primary pump designed to overcome the pressure loss in the boiler and piping to the secondary system delivering designed to deliver 120K BTU's to the secondary system, normally 1 1/4" pipe. Secondly, I would design the secondary piping to provide 4 gal/min for each of the four zones, normally 1 1/4" pipe. Each pump depending on the temperature of the water and pressure loss in the zone need to pump 4 gal/min thu its zone. This is so you get the maximum heat output in every emitter on that zone regardless of the water temperature. You need to install a Taco Acu-Flo balancing valve on the return of each zone and set it to 4 gal/ min. You need a differential pressure gauge to do that. Or, use a Caleffi Quicksetter balancing valve, I gave you a plug, 'Hot Rod'. You don't need a meter for that product. All this will maximize your heat output for your system.

I have done many systems such as yours and I tell my customers to set the thermostat and forget it, although some customers want the bedroom cooler at nite and I install a programmable thermostat for them. This works well for fast heat emitters and less so for in-floor heating (slow heat emitters).

Neal, you must cover the the pex lying on the ground. Take polyethylene 1/2 thick wall pipe insulation, not the self gluing kind unless you can get to the point of application, but the kind you split and put it on and tape it with duct tape and slide it back on the pex and add another piece and continuing until the pex is covered.

You must insulate the under floor. Dual pane windows would be the minimum requirement. Add more insulation in the attic if the existing insulation is of poor quality. You may not want to fork out the money for the improvements now, but you either pay up front or pay later with higher energy cost plus less comfort. I hope this helps.

HomerJSmith

Paul48 had a good comment.

Neal, there are only two way to get the comfort zone you desire.
1) Increase the radiation in the house envelope.
2) Decrease the radiation loss thru the house envelope.

HomerJSmith

Neal, I just re read your first post. You didn't say, but did mention glycol. Do you have Glyco in your system? If so what percent. Everything changes with glyco. You can lose 15 percent of your head energy for each pump, system pressure loss is greater and heat transfer from the fluid to the emitters and heat exchanger to the fluid is less than would be for water.

NealFoley

Yes, there is glycol. I don't know what percent. We're still trying to find someone other than the original installer to service the system. But a tag put on the boiler says is good to -30F!!!

That all being said, the system is working much better than before and using less energy to keep the house warmer thanks to the advise here.

NealFoley

> @HomerJSmith said:
> Neal, can you add panel radiators, increase your heat emitters?
>
This is certainly part of the overall plan.... Switch out the BB and put in panel rads over time.
>
> Neal, I don't know how your system was designed.

See photo below.

> Neal, you must cover the the pex lying on the ground. Take polyethylene 1/2 thick wall pipe insulation, not the self gluing kind unless you can get to the point of application, but the kind you split and put it on and tape it with duct tape and slide it back on the pex and add another piece and continuing until the pex is covered.

This is done.
>
> You must insulate the under floor. Dual pane windows would be the minimum requirement. Add more insulation in the attic if the existing insulation is of poor quality. You may not want to fork out the money for the improvements now, but you either pay up front or pay later with higher energy cost plus less comfort. I hope this helps.


Windows are all up to snuff. Insulting around foundation and under floor is an on going project. Air sealing and attic of main house was done in spring. The energy consumption was cut in half immediately.

NealFoley

Here's how the system is set up.

Ironman

Neal,
Can you post another pic from a little farther back?

It looks like the boiler pump is pumping into the house manifold instead of away from it. That's a big mistake, though it may not be obvious to many. You're probably not getting sufficient flow through the boiler when multiple circs are running.

hot_rod

We did a webinar few years back on using mod cons on HWBB. Properly designed and adjusted it works fine.

Here are a couple slides that shows how it can work.

Keep in mind, in most areas only a small % of the year you are at design conditions. This example was for Boston, MA.

The webinar, in 2015 is archived on the Caleffi You Tube channel.

bob eck

Question #1 is the element in the copper baseboard installed right? If installed sideways air can not flow through the aluminum fins and give off proper heat transfer.
Question #2 is there thick carpet right up to the bottom of the baseboard on the wall? You need air to go in the bottom of the baseboard and out the top. If there is carpet blocking incoming air the baseboard will not give off proper heat transfer.
Check that out.

mikeg2015

NealFoley said:

mikeg2015 said:

You might also check flow rate. Too low of flow rate and you lose capacity. Too high and the condensing boiler might be limited due to high return water temp. Just another variable.

I've been wondering about flow rate. Unfortunately there isn't much info I can go on. The system has almost no gauges. The pumps are Taco 007 F5s. So the rate could be anything.

The boiler requires a minimum of 3.5 gpm. I prefer alpha pumps cause you have some control and a readout.

From the screen it appears the water returning is within 5 degrese or so lower than outgoing once the system has fired.

I suppose one could limit the flow by cracking a valve closed a bit. But that's a risky, short term solution.

If you have approx. boiler inefficiency curves, you can calculate flow rate using Delta T and boiler output. On your screen you show firing rates.

So GPM * 500 * Delta T = BTU or with some algebra...

Or BTU/(500*deltaT) = GPM

Better to have pressure gauges, but this works too.

Also pressure gauges on the inlet and outlet of the boiler can be used to determine flow. the MFG will have pressure drop curves for the heat exchanger.

NealFoley

> @bob eck said:
> Question #1 is the element in the copper baseboard installed right? If installed sideways air can not flow through the aluminum fins and give off proper heat transfer.
> Question #2 is there thick carpet right up to the bottom of the baseboard on the wall? You need air to go in the bottom of the baseboard and out the top. If there is carpet blocking incoming air the baseboard will not give off proper heat transfer.
> Check that out.
>

The radiators are clear of obstructions, but most have a supply tube running across the top for the length of the run....

NealFoley

> @Ironman said:
> Neal,
> Can you post another pic from a little farther back?

It's in a tight cellar access. That's as far back as I can get without the door being in the way...
>
> It looks like the boiler pump is pumping into the house manifold instead of away from it. That's a big mistake, though it may not be obvious to many. You're probably not getting sufficient flow through the boiler when multiple circs are running.

I wondered about that. Is it right that the pump leg is tied to both the outgoing manifold and the return?. Not how I would have done it....

If I can, will switching the pump around help?