Oil Fired Boiler With tankless Coil conversion to what?

Hello All,

I am a homeowner with no experience at all with home heating/plumbing so please ask if more detail is needed.

I have a Kerr Comet 145 boiler with a tankless coil for DHW. One year ago I had minisplits installed to try and reduce our heating costs, but after one year the savings were negligible. I am not sure why, but I am thinking it is because my DHW is still being provided by the tankless coil which is extremely inefficient based on what I've read (especially when not being used in combination for home heating which is the case in my situation now). My oil costs did decrease (about 30%), but I still spent around $1500 in oil ($2300 the previous year) at around $1/LITRE (we're in Canada)...that was on hot water, the cost to keep the boiler running year round, and the minimal hot water baseboard used to keep the basement at around 10-12 degrees celcius during the winter. To me $1500 seems really high, but maybe I am way off base...in my mind the majority of that is hot water. Is there any real way to estimate what the breakdown would be? We are an average family of 3.

If you agree that it seems high and is most likely due to DHW then I am looking for recommendations about what to do to try and begin seeing savings if at all possible. My initial thought was to install an electric hot water tank and shut the boiler off except during extremely cold nights in the winter when the minisplits can't keep up and install electric baseboard heat in the basement to keep it at 10 degrees, but I'm reading that this poses problems because I shouldn't "cold start" my boiler (leaks, shortening life span etc).

Alternatively, I'd have to leave the boiler running all year round (again, is this a huge expense? is there a way to decrease the cost) like I do now and install an electric hot water heater (or some other storage device)?

Or is there a totally different solution that I am not seeing? I don't want to spend a lot more money to swap boilers etc, but after hearing glorious things about saving money by installing minisplits I am a little disappointed to say the least.

I am really confused and any help would be appreciated.

Thanks,

jek

The $1500 is what it costs for oil-fired hot water in a boiler with high standby losses. By having to keep the boiler at high temp (160-180F) to deliver reasonable hot water performance, the standby losses are about 1.5x what it would be if the standby temp was 135-145F, and more than 2x what it would be running it cold-start (if it's a boiler that won't be damaged by cold-starting.) Electric hot water is very likely to be your cheapest/best option here if you are heating primarily with mini-splits.

If you're moth-balling the oil system and only firing it up as your "hail Mary" backup for the mini-splits, the standby loss heat normally heating up the basement isn't there. If the basement isn't already air-sealed and insulated (and it sounds like it isn't if it needs baseboards to keep it above 10C), it's worth it. In a NS climate with a 20C rooms above it a tight basement with R15 or better on the walls would never drop below 15C, let alone 10C. Insulating foundations has to be done carefully in a climate & construction-specific way to avoid moisture related issues- the practice of installing a batt-insulated studwall with interior polyethylene vapor barrier that sort-of-works in Saskatchewan is too prone to mold/rot issues in the maritimes. But 3-5cm of closed cell foam (sprayed or rigid) up against the foundation, seams & edges sealed with appropriate tapes &/or can-foam, with a non-structural studwall on the interior insulated with rock wool and NO vapor barrier works pretty well and delivers an R-value in the low 20s (making the basement the warmest place in the house when it hits -25C outdoors ). There are many particulars to attend to- if you want to take on that project I can elaborate on that a bit. (Or you can search the remodel forum on this site for basement insulation- it's a topic covered fairly regularly here.)

Thanks for the response Dana. The basement is insulated (not finished, but drywall is up), but on particularly cold nights (-10 to -20C) the boiler does kick in occasionally to raise the temp...quite infrequently. I'll definitely take your ideas into consideration though since you raise a good point about increasing R values for sure.

I'm not overly keen on shutting my boiler down due to the problems I mentioned above as I don't think it's intended to have cold starts, but what about working towards an end goal like this:

1. Installing an indirect water heater for now (instead of electric)...would this still potentially give me savings on my hot water compared to the tankless coil? What is the average life span of IWH? And would there be some sort of ideal boiler settings that would avoid cold starts, but still reduce the number of times the boiler starts and stops? Like lowering the temp on the boiler? Or would I just leave the boiler alone and install the IWH (by "I" I mean someone else like a heating expert)?

2. When the current boiler needs to be replaced I was thinking about then putting in a "cold start" boiler to complement the IWH which seems to me to be very efficient for hot water while still providing heat (if I ever decide not to replace the minisplits if they should stop working). That may be years down the road, but at least I'd already have the IWH installed.

This all hinges on seeing some sort of savings now if I were to install an IWH which is something I am not sure of. Otherwise, should I just got with the electric hot water heater? I still wouldn't want to shut down the boiler though so I feel like the IWH might be a better addition in the bigger picture. None of this takes into consideration what the prices of oil and electric will do over the next few years, but my instincts suggest they'll both have similar increases.

Thoughts?

Ok, so the Kerr Comet is a pretty decent boiler. Its steel, not cast iron and it claims to run at about 86% efficiency which is pretty good for an oil fired, non condensing boiler. It is steel so cold firing it will not bother anything at all although its worth keeping an eye on the tankless coil gasket and maybe tightening the nuts a bit (don't snap them off) if its going to leak, it will be at the coil gasket. Next is to install an indirect. Something like a Super-Stor SS40 for your domestic hot water and either bypass the low limit or change the control to a Honeywell L8148. Some sort of re-set control should also be installed and since you don't plan on using it much for heat it would be a real good idea to put some anti-freeze into the system to protect the pipes.

Thank-you for the advice about the leaks...that's somewhat comforting to know. In your opinion would the life of the boiler be significantly shortened though? Or would the call for hot water from the indirect be enough to help avoid some problems?

One other thing I thought of last night was what would peoples thoughts would be on switching the oil fired boiler to electric? Could electric boilers be cold started without any issues or are the "cold start" electric boilers too? Where I am, electric and oil are currently $1.10/L and electric is $0.137 KWH I think, but I see oil continuing to increase faster than electric. Could I then put in an efficient electric hot water heater and then just the electric boiler unless for heat? Not sure how electric boilers compare in price to oil boilers though...trying to figure out the safest, most cost effective and efficient route.

Merci!

It will NOT shorten the life of the boiler. You will not have problems using the boiler just for domestic hot water.
Electric heat would be a real bad investment.
Maybe an electric water heater if only because the initial investment is less than an indirect and the controls needed but in the long run you will do better with an indirect off the boiler.

Personally, if it were mine I would do the following

1 Cold start the boiler

2 Install a Super-Stor SS40

3 Install a temperature re-set controller so the boiler doesn't have to run at 200 degrees on warm days

4 Bring outside combustion air to the oil burner

5 If the burner doesnt have an internal damper that closes on the off cycle I would install one either in the burner or the chimney and reduce the stand-by loss. Riello burners come with the damper

6 Have a competent technician slightly downfire the boiler and set it up for maximum efficiency

At $/ltr oil in an 86% burner and $0.137 electricity it'll be slightly cheaper to do your hot water with oil.

A liter of heating oil runs about 36,500BTU/hr source-fuel, so at 86% efficiency you get ~31,390 BTU/of heat into the tank for about one Loony, plus some small amount for the pump power use.

With $0.137/kwh electricity, you get 3412 BTU into the tank. Normalizing that to BTU/Loony you get 3412/$0.137= 24,905 BTU/$

If you used a heat pump water heater it would dehumidify your basement, and somewhat split the difference in oil/electric water heating costs during the heating season, and deliver about 55,000BTU/$ during the summer months. That would likely be the cheapest hot water use.

Cold firing the boiler WILL make the basement run cooler. With an insulated basement hitting 10C and below its likely that you have significant air leakage down there. Sealing the foundation sill and band joist with FrothPak or can foam would be a good start- wait for days when it's above 10C outside if you want the stuff to stick, but while it's still cold out get a $50-75 pistol grip infra-red thermometer and hunt down the cold spots and mark them, since that's where the majority of the leakage is. If you turn on all of your kitchen & bath exhaust, and the clothes-dryer too it will pull in more air, making the major leakage points easier to spot.

How is your basement insulated?

Edited to add:

If you are doing the vast majority of your space heating with the mini-splits, the as-used efficiency of the boiler is going to drop significantly, even if you cold-start it and use heat-purge economizing controllers that dump the boiler heat into the indirect tank. With retrofit controllers you'd be lucky to break 70% efficiency in water-heating-only mode, and without them it would be tough to break 50%. See Table 2 of this document. (System # 3 is a cold-startable steel boiler with a fairly sophisticated heat purge controller that comes as part of the system, not a retrofit.)

Thanks Dana for the suggestions. A comment about your #s that I'm hoping you can clarify. You mention "A liter of heating oil runs about 36,500BTU/hr source-fuel, so at 86% efficiency you get ~31,390 BTU/of heat into the tank for about one Loony, plus some small amount for the pump power use." However, am I safe in saying that in the summer there is no way I am running at 86% efficiency? More like 50% (since I wouldn't be heating in the summer)? So electric hot water would be the cheaper alternative at least in the summer? And maybe even in the winter since I don't use the boiler much for heating?

Also, could you elaborate on the heat pump water heater? What do you mean that I could split the difference in oil/electric water heating costs in the winter?

I'm starting to think (heat pump water heater aside) that an electric hot water heater in the summer (boiler off) and using turning the boiler on during the heating season (like I do now) while using the electric hot water heater as an indirect of sorts might be my best option....or turning down the boiler a little in the winter and just using the electric hot water heater to supply the hot water. Also, making those tweaks with the controllers you mentioned and insulating will help in the winter too.

I cannot wrap my head around using an indirect during the summer being less expensive than the electric hot water heater and I also can't see how I'd have better savings year round...that is specific to my situation since I use minisplits to heat and don't have a cold start boiler.

Thank again experts.

In summer it'll be running substantially under 86% efficiency, but with a heat-purging boiler control (Intellicon HW+ or similar) and cold-starting you'll probably be north of 60%, maybe even 70% (but don't count on it.) The Energy Kintetic System 2000 hits around 75% efficiency in hot-water only mode, but it is a highly engineered finely tweaked product designed for always purging heat into the indirect. See the measured performance of system #3 in Table 2, and detailed in Appendix #3 of this document (which I linked to previously.) That unit was a System 2000.

By heat purging the boiler into the indirect on every burn and letting it cool rather than maintaining temp it drastically reduces the idling standby losses, it can do OK (even in summer.) If you hit as high as 70% efficiency (like the EK System 2K) in hot water only mode with a retrofit heat-purging controller you'd be about dead-even with a standard electric hot water heater on summertime operating costs: (70% / 86%) x 31,390 BTU/$= 25,550 BTU/$, compared to 24,905 BTU/$ with the electric tank.

Heat pump water heaters take about half of their heat from their surroundings, the rest from the power used to run them. This means during the heating season half of the heat is being made up for by the heating system (at whatever efficiency it's operating), and half it the power input to the HW heater. During the summer when the heating system isn't running it's cooling off an dehumidifying the room where it's located, reducing the the air conditioning loads. The sensible cooling loads in your neighborhood are all but non-existent, but the humidity loads are real, especially in a somewhat cool basement.

That means that during the summer months it's literally half the cost (or less) of running an electric hot water heater, and during the heating season half the heat is the cost of oil burned at 85% efficiency, while the other half of the energy is at standard electric HW heater cost. That's what I mean by "...split the difference...".

Okay. I think I get it a little more now.

I'm hoping this is my last post, but I still have a few questions.

Is there any less wear and tear on the boiler in the summer by just shutting it down completely (using electric hot water) compared to cold starting it all summer and heat purging it into an indirect? More condensation risk one way vs the other? Apart from the heat pump water heater (which are out of my price range realistically speaking), it appears that it's a toss up between an indirect or electric hot water heater for savings in the summer. And if that's the case then the EHW wins just due to the cost of installation alone for me I think. But that only takes the summer into consideration...

I think another thing that confuses me is when you factor in winter heating plus hot water for the winter. The efficiency ratings trip me up. To me the 86% efficiency rating is based on if I was using the boiler as the primary source to heat my home in the winter (which I'm not) otherwise the tankless coil hot water component still kills me (not as much as the summer, but pretty close). In the winter I call for a lot more hot water when the boiler wouldn't be hot (just like the summer) due to how I heat the house. That leaves me wondering which of the two options (indirect/EHW) are most efficient in my particular case for the winter. I think that both options would reduce my winter heating/HW costs, but would there be a major difference between the two? Some points to mention:
- The main calls I get for heat from the boiler are on colder days when the basement requires the boiler to fire (no minisplit there) or colder nights when the minisplits on the main level/upstairs need some help...so I will still need the boiler heat from time to time for sure.
- Would I want to leave the boiler on all winter regardless of whether using indirect or EHW?
- For EHW could I reduce the oil boiler temp a little to maximize savings since it'd only be needed for heating occasionally? Or would I just cold start the boiler all winter? That seems like a bad idea to my....just saying.
- I suspect I'd let the boiler run at regular temps with an indirect since it would be used for some heat/hot water or would I cold start it all winter as well?
-Out of these different combinations from the last two points is there a "right" choice (is one far superior to the others meaning I'm totally missing something) or am I splitting hairs because the two options would be so close? Taking summer and winter into consideration and all costs involved?

I think that's about it. I'd like to make up my mind before spring so I can at least start seeing savings come that time of year.

Again, thanks to all of you.