Efficient Replacement Options of 25 Year Old Propane Boiler/Indirect Heater

connor016

So my hot water went out again and I think it is due to my automatic vent not operating properly. I hit the manual switch to open the motor and then the boiler fired up. Once it reaches temp the vent doesn't close so I am assuming it may be due to the control in the aquastat but I will have to dig into it more. Regardless this got me thinking that the system is 25 years old and the propane bill is $$.

Heating System Specs:
Current Boiler: Weil-McLain CG-6-SPDN, 145kBtu/hr DOE Heating Capacity, 80.5 AFUE
Indirect Water Heater: Heat Flo HF-40 (40 Gal)

The home is in Salida, CO built in 97 and is nearly 7,000ft total but main living area is approx 3,000 and an in-law unit of about 1,000. Propane the first winter probably averaged around $500 per month. I ended up putting in a 7.5kW solar system and a LG 24k Btu 3 zone mini split system that heats two bedrooms and a living room area to help offset the hydronic heating. I also installed a firewood stove this year too so I am hoping the hydronic system sees little use. It does heat the in-law unit which is usually occupied for a few months in the winter.


Questions:
1) Could I add an electric water heater + a new combination boiler such as Noritz NRCB199? My thought with a combination boiler is that since the home hot water supply recirculates in order to have hot water on demand the electric water heater can likely keep up with the losses from recirculation which my solar can help with. I don't know if this is practical or if I should just use a new combination boiler only. With these it looks like there isn't a holding tank required but my concern would be with a recirculating system it may always be on or constantly turning on/off.
2) Is there a practical way to go away from propane altogether? I don't think I want to spend $$$ for anything like geothermal and it seems like electric boilers use tons of energy that my solar system would not be adequate to support as it is currently fairly neutral for providing power. I assume next year there will be even more power consumption with the mini split system that was installed about 2 months ago. My solar output this year was 13.8MWh and net usage around 1.6MWh Given the amount of sun in Colorado maybe adding a solar water heating system might make sense.
3) It seems like with a combo boiler or just an independent hot water supply might be more efficient if I can turn off the hydronic system altogether in the summer. My understanding is that temp has to be above the water temp on the indirect system and regardless of the zones being off the boiler will still maintain that higher temp and still recirculate through the system in a loop before the zone valves.
4) Any other recommendations?

Thanks in advance!

Jamie Hall

Well, your solar output is around 38 KWh on a daily average; given a generous assumption of 6 hours of usable sunshine per day, that's around 6 KW.. Your propane boiler is rated at about 43 KW -- so even when the sun is shining your solar electric array won't come close to meeting the power of the propane boiler. When the sun isn't shining, of course...

Welcome to reality.

The question becomes, really, what do you want? You can have low carbon impact. You can have reasonable cost. You can have reasonable efficiency. You can only have two of the three, so you really need to decide.

Electric resistance heating for the hot water depends on the electric grid. It is the least efficient and most carbon intensive of the possible choices, If you use relatively little hot water on a daily basis you might be able to power a heat pump hot water heater (with the resistance booster cut out) with your solar array If you had enough hot water storage, you might get away with not requiring battery electrical storage. Solar hot water makes sense in a sunny environment, although done right it is pricey. The recirculation, while nice to have, does not help your efficiency on hot water at all, and would need to be factored in in sizing and designing the system.

In my view, ignoring for the moment the possibility of the supply of LP being cut off by government action, the best bet would be a new high efficiency LP boiler for your heating needs. Not that the W-M is bad (the problem with the automatic damper is a simple repair having nothing to do with the boiler). I'm not sure whether I'd keep the indirect or whether I would choose an on-demand LP water heater -- or if the hot water demand locations are in two groups, possibly two of them -- and get rid of the recirculation.

Hot_water_fan

Right now, unfortunately air to water heat pump options are limited in number/manufacturer and have some limitations for retrofits (type of emitter (floor, baseboard, etc) matters a lot). Perhaps in time, options will improve. If you went with an existing air-to-water option, you could ditch propane depending on the heat loss and existing radiation. If they’re not adequate, you may need a backup for the coldest days (like a repaired old boiler or an electric boiler). 

Air-to-air (minisplit or not, ducted or not), is much more common in the US, so options are bountiful. 

https://www.greenbuildingadvisor.com/article/out-with-the-old-in-with-the-new

Use this link to calculate your heat loss, it’s simple and is the most important step.

Everyone’s situation is different, but low carbon, low cost and high efficiency can all be had. 

connor016

Appreciate the feedback. I knew after doing some basic calcs on an electric boiler it did not make sense. It sounds like I should just go with a LP combo boiler. There are multiple areas that use hot water scattered throughout the home so I don't think multiple on demand units would make sense for hot water since I would still need hot water for the hydronic system going there.

I may expand my solar to a 10kw system and end up putting another multi unit mini split for the in-law unit and spare bedroom that are currently only on hydronic heat. At that point the boiler output would probably need to be minimal.

I am thinking a good compromise might be a newer LP combo boiler. My main question if that would be a good direction is do I need a holding tank if I have a recirculating system? Should I eliminate the recirculating system? Currently there would be areas that are approx 75ft that use hot water so eliminating the recirculation may waste a fair amount of water (although I am on a well). Potentially I could only turn on the recirculating pump when the further areas need hot water quickly (such as the further in-law unit). I assume if it is recirculating without a holding tank then then the combo LP boiler would be running the majority of the time due to the small amount of water in the system that would have a fair amount of heat loss after recirculation.

Hot_water_fan

I don’t see why you’d go with a combi if you have an existing indirect - it’ll have lower capacity and tankless is generally a worse experience. A condensing boiler (non-combi) will work just fine and be as efficient. An independent water heater also makes more sense than a combi. Domestic water heating is a very small fraction of your energy use anyway. 

Daveinscranton

I could not be happier with the Triangle Tube Instinct that just went in.  Great mod con boiler. Comes with propane conversion parts.  You or the installer will want to pay attention to the instructions if you go that way.

Best wishes.

JakeCK

You're going to replace your 25yr old boiler because the auto damper failed? 

 

Are there other efficiency upgrades you could tackle first? More insulation in the attic? Weather sealing? 

I don't see a replacement modcon having a positive ROI for over a decade, if ever. 

Maybe abandoning the indirect for a heat pump water heater to take advantage of your solar? That would have a quicker roi.

hot_rod

It would be nice if your indirect had an electric element, a solar tank. Then your PV could go directly to the tank, possibly covering all the DHW in summer months. Check out the Sun Bandit system out of Colorado it used a few dedicated modules direct to the element 

connor016

I am not replacing due to the damper malfunction that was an easy fix but as I mentioned it got me thinking it is 25 years old and I prefer to take care of these things in advance before you are in a bind with no hot water/heat in the middle of winter which is why I am asking for advice here for more energy efficient options. Just going with a newer boiler looks like I can increase efficiency by 15% which could probably pay for itself within a few years.

Seems to be a lot of opinions and options on which way to go which is why I appreciate all the input as I am just beginning to look into this. It sounds like the easiest and cheapest is just go with a newer condensing boiler and use the indirect tank assuming a 25 year old tank has a long life expectancy (not sure what is normal for those). To me it seems like a combi would be more efficient since it looks like combis have two heating elements so you don't have to keep a larger burner going in the summer just to recirculate the indirect system and I assume it is still recirculating the hydronic loop before the zones. Essentially this could be turned off in the summer. I like the idea of an electric element but I do typically come out about neutral so far on my solar system but I can still expand it from a 7.5kW system to 10kW with the same inverter. The sun bandit looks interesting but I assume it would be more cost effective to add the extra 2.5kW solar system and then get an electric water heater vs going with their system. Main advantage I see with them is it works during a power outage unlike a grid tied system. I am curious if people have used the combi boiler with an electric water heater holding tank. I am just not sure how they would work in series and with a recirculating system. Ideally you could set temp higher on the unit you want to consume more power (electric vs LP) but have no idea if that would work. Also not sure on a combi system if it automatically turns on when it sees any flow regardless of temp as that wouldn't work well with the recirculating system.

For a smaller home I have installed a tankless hot water system and actually really liked it but that was a very small home and don't know how well it would work with a larger home.

Jamie Hall

I doubt very much that you will get 15% efficiency improvement. That would be assuming that tour existing boiler was only 81% (it's likely more, unless it hasn't been attended to lately) and that you can always get the advertised 96% out of a condensing boiler, which is very unlikely indeed (that's a little like saying I can get 18 mpg out of my 27 year old truck. Which is perfectly true -- at a steady 55 on more or less level roads, like maybe northern Indiana. Otherwise, not so much...)

But -- good luck! As they say, your mileage may vary.

connor016

Yeah the 15% is solely based off of the energy rating on the unit (old one is rated at 80%) and I know what you actually get varies depending on how your hydronic/hot water supply systems are set up. To me it is becoming pretty obvious the recirculating system is very inefficient. I am going to turn off the recirculating pump for a couple of days to get an idea of the delay on hot water and if it isn't too bad then a combi boiler alone may be the way to go without a tank/recirculating system.

Hot_water_fan

To me it seems like a combi would be more efficient since it looks like combis have two heating elements so you don't have to keep a larger burner going in the summer just to recirculate the indirect system and I assume it is still recirculating the hydronic loop before the zones. 

This is a misunderstanding of how both  combi and mod con non-combi work. The heating loops will be off during the summer and the boiler will not be kept at a high temperature (this is called warm weather shut off). Also, the burner needed for on-demand water heating is much larger than the what a indirect would need (because of the storage), but that’s mostly irrelevant to efficiency. 

Regardless, the largest savings will not be on the DHW side unless you have abnormal demand - reducing water temperatures and limiting idle loss on the heating side is where the waste is. 

Jamie’s right about AFUE being imperfect (humans you know?) but it goes in both directions. You could save 30+% if the stars align. 

connor016

Thanks for the clarification on the systems. With my current older boiler is there not idle loss in the summer on the hydronic heating side as I don't think there is a summer shutoff mode? My understanding is it is set at a target temp and there is a pump that keeps the water recirculating through the hydronic loop. Off of the loop there are zones controlled by thermostats/valves. In the summer the valves will never be open but doesn't the loop still circulate and maintain the high temp for the hydronic heat or does the pump turn off and not recirculate when there isn't demand? I know there is a second valve that controls the circulation to the indirect system based on the water temp but in the summer when the heating isn't being used I assume that is a less efficient way to heat water only. Maybe that is insignificant though compared to the hydronic heating. Luckily with the mini split systems + fireplace I will significantly reduce the use of the boiler system.

connor016

Below is just an image of the current boiler/indirect system for reference. I just have the cover off the boiler for now as I was diagnosing the vent issue. Probably will cost me a fortune in copper to re-route things if needed!

Daveinscranton

I am in the mod/con boiler camp.  I believe the science to be non trivial in practical application. If you view it as a hobby, or entertainment, or a science experiment, it seems to go well.  (My friends believe it to be mental illness and are sick of my mutterings).  

Near as I can tell, installation is everything.  As is maintenance, including water quality.  It took me a while to dial mine in.  Pretty easy to get your condensing happening where it will do no good like in the flue as it runs through an unheated space.  The amount of condensate will then goad you into thinking you are maximizing the efficiency when you are not.

The newer stuff looks much improved over the first generation of mod/con boilers.  If I knew who to call, I would have hired a pro.  I didn’t know so it became a pet project.  Took the fear out of it though because I know what it is doing and why.

Best wishes.

Hot_water_fan

With my current older boiler is there not idle loss in the summer on the hydronic heating side as I don't think there is a summer shutoff mode?

That’s exactly right! Major idle loss in the summer, but it’s from the boiler itself, not the tiny loop (which you could insulate). For reference, a house your size would have about 7,000 feet of tubing for a radiant floor, so this loop’s heat output is a rounding error. This is why newer boilers have the WWSD option. Your indirect, as currently set up, is probably 40% efficient during the summer. That’s still likely only $5-15 wasted per month. 

The savings come from reduced water temperatures for central heating and lower idle losses (often achieved via modulation). 

You’re right about fuel switching: using heat pumps will probably be substantially cheaper than propane. 

This poster saved 34% switching to a condensing boiler. Your house should have a higher heat loss, so if the percentage is similar, the $ will be higher (especially since propane is so expensive). 

https://forum.heatinghelp.com/discussion/185035/one-year-ng-utilization

connor016

That is a pretty impressive % reduction. I went through my propane usage the last year and found I was using around 7-9 gal per day in the winter a year ago and around 2 gal per day in the summer. Since installing the mini-split units and fireplace (which has been used minimally due to having banked solar kWh) my usage the last two months was around 2 gal per day so far this winter so a significant reduction. Energy usage went up by only about 150 kWh in December with having the mini-splits vs last year. This is very limited data and avg temps this December were higher but it is definitely trending in the right direction. The billing varies and that assumes they are always topping off the tank but it would be great to get down to averaging 2-3 gal per day in the winter so I could fill my 500 gal tank before prices spike.

I also came across this thread where they used an electric water heater with a combi boiler with good results:
https://forum.heatinghelp.com/discussion/161749/combi-boiler-w-domestic-recirc-buffer-tank

I am thinking of two options and interested in feedback:

1) Combi Boiler + Hybrid 40 gal Tank + Recirculating System- Have these in the same boiler room and replace the indirect with the hybrid tank. The goal would be to keep the 40gal tank heated and recirculating system going with electric only. During hot water usage the combi system would kick in. Downside might be that the room this is in is attached to a garage/etc so the heat pump might not be as effective as the garage is not heated. I could still locate the hybrid tank elsewhere in the home in a more central location too.

2) Non-recirculating system of above- Have the 40 gal hybrid tank further away from combi system for spare bath/2 kitchens. I turned off my recirc pump today and the further kitchen/bath take over a minute to heat up so if I used a 40 gal tank located closer to the further hot water areas then those could be downstream of the tank for faster hot water supply.

Hot_water_fan

A combi boiler only provides space savings, which you don’t need considering you already have made space for an indirect. 

Why not a 80 gallon hybrid and call it a day? It doesn’t have to be connected to the boiler at all. Most efficient option, still has high capacity. You can fit in wherever makes the most sense. 

connor016

I would prefer to have the dual fuel option if there isn't a big decrease in efficiency/increase in cost and it looks like there isn't a big cost difference with the combi system. It doesn't seem like that would be any less efficient but I guess you would need a bypass around the combi if you were to use electric only unless you can disable the heating on the combi. It looks like avg consumption is around 2.2 MWh/yr of a hybrid water system which adding another 2.5kW to the solar system should easily account for. I would need to further analyze the costs of fuel/investments in systems/etc.

Hot_water_fan

I’d keep the indirect and add an efficient boiler in that case. Combis are really compromises for zero benefit. 
What’s the electricity rate you pay? Solar is great of course but you could be significantly cheaper than propane using just grid electricity. 

Jamie Hall

I have always mistrusted efficiency comparisons -- "I did this and saved 30%" -- not that the statement may not be true -- it may well be true -- but that it may not be complete. Did anything -- anything -- else change? Back in a much earlier life I had the same problem with cars -- "Wow! I added this new widget, and now I get 20% better mileage -- or more easy to compare -- as I did more than once! -- I cut my quarter time by 2 seconds!". Which I usually countered with something like really? See you down at the strip -- where I'd usually blow their doors off, but that's another story.

hot_rod

How much is LP running a gallon, how much is your KWh when you have to buy

the biggest problem is the wide variation in LP prices. Any other appliances on Lp?

www.coalpail.com has a great fuel cost calculator. See where LP and electric meet.

Right now my 12 kWh electric resistance boiler is less $$ to run with Lp at 3.79/ gallon. 




in your case a  heat pumps may be the least expensive option. Current air to water cold climate heat pumps can run 3 COP if you have low temperature 120f heat emitters

I like combi boilers if you stick with Lp, it really comes down to your hot water needs when considering a combi

Solar pre heat for the combi should all but eliminate summer Lp consumption

Do you own your Lp tanks, pre season buys are the best way to use Lp

EBEBRATT-Ed

@connor016

Mod cons versus CI the debate continues

The both have pros and cons. You already know what CI is and replacing it with CI won't save anything.

Mod cons have a (maybe) 15 year life if maintained well. We have seen some boiler mfgs where parts become scarce after 10-15 years. CI not so much you can usually keep them running and your CI could go another 15 yrs. I just tossed my CI it was in the house when I bought the place 35 years ago so it was probably 40-45 years old.


But mod cons will save some fuel especially if they can run low temp and they modulate to meet the load two big advantages

Mod cons require a "higher quality" service tech in this age of poor quality techs the are fewer and far between (unless you dyI)

In response to your question 3 in the first post, the boiler should not be maintaining hot water for the indirect. You have 1 pump with two zone valves (although 1 valve is not shown). The zone valve for heat should keep the hot boiler water out of the heating zone in the summer and the boiler should be off until the control in the indirect calls for hot water

pecmsg

EBEBRATT-Ed said:

@connor016

Mod cons versus CI the debate continues

The both have pros and cons. You already know what CI is and replacing it with CI won't save anything.


But mod cons will save some fuel especially if they can run low temp and they modulate to meet the load two big advantages

Mod cons require a "higher quality" service tech in this age of poor quality techs the are fewer and far between (unless you dyI)

And that shortage of Qualified Tech's will continue for quite a while.

connor016

My last propane fill was @ 2.61/gal and I haven't been charged for electric due to solar since the beginning of 2021 which was @ .13/kwh. After searching a bit it looks like it may have gone up all the way to .17. Based on coalpail that is 3,361 for propane per 100 million btu and 4,982/100millBTU for electric resistance. Thanks for the clarification on the indirect system...the other valve my just be in the crawl space. I will probably continue with this through the winter season and keep an eye on my usage now with a mini split system installed and a wood burning stove and reevaluate this summer after having some more data.

hot_rod

Assuming you are not paying street price for firewood, the combination of wood stove and mini splits with a PV array must be the least expensive heat option.