Mitigating effects of oversized of Alpine 105 Mod Con boiler in small house

Was just installed by my landlord in a small, early 1900's duplex of 1,100 sf, two story, unfinished drafty basement, insulated attic, no insulation in the walls, ten large, cheap, older vinyl replacement windows with no additional storms, in Newton, MA just outside Boston. Just did the radiator calculation and have roughly 213 sf. of cast iron radiators in one zone plus the 45 gal Super Stor on its own zone. Boiler was piped just like the instruction manual indicates, with a primary and secondary loop (even though it's only one zone of heat). What can be done to maximize efficiency given the too big boiler? I realize there will be a short cycling problem on the heat loop. We have the outside temp sensor hooked up. I can't install a buffer tank because I don't own the place. Have not used the heat yet.

 

I have an Alpine 150 model with a 50 gal indirect installed in a house a little bigger than that. You can adjust the maximum fan speed for both heating and hot water calls. This is what I set much down to the minimum for heat and whatever number works for hot water so that one cycle meets the demand of the tank. If you have the newer version with the color screen you may have more options than my 3 year old model.

 

Thanks for the tip. The plumber is a hack but luckily his plumbing looks just like the diagram in the instruction manual. He did minimal setup on the boiler itself from what I could see but it hums nicely on hot water calls maintaining a constant 170 degrees as it satisfies the set point (I like it hot so it's 140). The fan speed for hot water calls sounds about right if it's maintaining a very steady 170 in the boiler. Are you getting it to condense on heat calls? What kind of radiation do you have and how many zones? What is the typical mid winter burn time on a heat call? I have a feeling I'm going to get smoked out of my house this winter with excess heat to keep it from massively short cycling. As we get into the cold weather I will investigate limiting the fan speed on heat calls.

 

First, call it a boiler, not a furnace. In the HVAC biz furnace refers to an air handler with a burner where the heat is delivered with hot air.

At 140F AWT with 213 square feet EDR you get about 20,000 BTU/hr out of the radiators, which balances well with the minimum fire output of of the ALP105, but it's getting very little condensing.

At 120F AWT (what you would need to hit the mid-90s for combustion efficiency) you'd be getting 11,000 BTU/hr out of the rads, which is barely more than half the min-fire output.

The thermal mass of water in the radiators can help- a lot! If it's getting 3 minute burns and only a handful of burns per hour it isn't going to destroy the efficiency or wear out the boiler. To max the efficiency you need to set it up with the return water temperature at the lowest it can be, with the flow/delta-T on the boiler still within spec, and not short cycling. With the thermal mass of the water in the system you may be just fine with 110F return water and it cycling on/off 5-6x /hr.

Start playing with the outdoor reset curve, during milder weather like this by dropping the parameter 5 (the output temp when it's warmer outside) to 80-90F or something, then go crank the thermostat up 5 degrees above the current room temp, then monitor the burn cycles and the output & return temps of the boiler as it tries to bring the house up to temp. If it's giving you consistent burns of 150 seconds or better and fewer than 10 burns/hr at effectively ZERO output from the radiators you have enough thermal mass in the system to work with. Bumping the parameter 5 temp up to 100F or 110F or something may be necessary for it to actually keep up with the load when it's in the mid-50s or so, and that will stretch the burn times a bit, and yield fewer burns per hour.

Then it's a matter of tweaking that warm-outdoors end of the curve to where the boilers water temp is high enough to just barely keep up with the load overnight. When it gets cooler outside you can then start dropping parameter 4 (the output temperature for when it's cold outside), until it DOESN'T quite keep up overnight, then nudge it up a degree or three at a time until it does. If you dial it in well enough on both ends it becomes a "set and forget" approach on the thermostat, since it won't have enough extra output from the rads to provide a fast recovery time from overnight setbacks, but the boiler will run at the highest possible efficiency to make up for it.

BTW: In a rented multi-family in MA you can still get substantial MassSave rebates on air sealing and insulation. If you cut a deal with the landlord to reimburse you for some or all of your net out of pocket, that's legal too, but if you're the person on the gas bill, you are the one initially paying the contractor and collecting the rebate (typically 75%) from the program.

 

Dana,

Thank you very much for this valuable info, especially which codes to tweak on the menu. Do I need to mess with the maximum fan speeds on either the heat or DHW zone? The boiler is running at a steady 170 degrees for 5 to 10 minutes fulfilling my 45 gal super store at 140 degrees set point. By the way, how do you measure the return water temperature to the boiler?

Last winter, I set my thermostat to 62 and left it there pretty much 24/7 the whole winter. What would you suggest this winter with the new boiler to exploit the tweaking you just told me about. I find 61 to 65 quite comfortable, never felt the need for 68 or more and it's just me living here. Also, due to there being too much radiation on the second floor (34 sections on first, 31 sections on second) and an open stairway allowing a lot of heat to rise, the second floor is always warmer than the first by probably 5 to 10 degrees or more. I certainly don't want to shut down any radiators because I'm already short radiation area. Bedrooms are on the second floor. It should have more on the first floor but it doesn't.

Thanks again for the help. I just sold a house out your way a few months back.

Dave

 

I thought the ALPxxx series would display those numbers(?), which probably requires some button-pushes to get to. Cozy up with the manual as a bedtime story for a few nights to figure it all out- I'm sure it's in there. (I've never owned or tweaked-in that boiler myself.) The part for tweaking the temperatures during domestic hot water temp starts on page 51, the outdoor reset section starts on page 55. You may have to read through it several times to figure out the programming steps. Like most boiler manuals, they don't explain how to dial it in for maximum efficiency & comfort.

Part of the temperature difference between the first & second floors is convection, but a large part of it is stack effect infiltration in the wall cavities, since the warmer air in the studwall cavities is exiting in the attic or eaves, sucking cold air into the walls at the first floor or basement. Also, when the radiation was first installed there was probably no attic insulation either, which means the upper floor had more exterior surface area to lose heat from, but with even R19 in the attic a large chunk of the heat load upstairs went away, leading to a temperature imbalance between floors.

Air-sealing both the basement exterior walls/doors/windows and the bottom & top of the studwall bays will help. Air sealing is necessary but not sufficient- insulating the walls after air sealing will help even more. (Blown cellulose is probably going to be the cheapest and best solution there.)

With the condensing boiler in the basement instead of a lossy high-mass oil fired behemoth the basement temp is going to be lower than in prior years too, since the standby losses will be a fraction of what they had been. I'm not sure if MassSave is subsidising insulation for unfinished basements, but they should at least be able to help out on the air-sealing front. If you can get your landlord on board with it, there are some relatively cheap ways to DIY-insulate the basement too. None of the insulation solutions will pay off in fuel savings in 1-2 heating seasons, but they will pay off in comfort.

Subsidized (or DIY) air sealing could pay off in a single heating season though, if you train yourself on how to really do it, and figure out where the big leaks are. (It's easier to find the leaks with a blower door test using infra-red imagine, but if you have time for sleuthing you can figure out most of it using other means.)

 

I've already got the manual on my bedside table I must be an uber geek to be doing this. I'm stuck with the basement because it's a side by side duplex with the landlord next door and the two basements are open to each other. I've broached the air sealing project, he's on the slow train, we'll see. I'm just glad to have gotten rid of the antique oil ark that was probably running at 40% last winter. I probably burned in the neighborhood of 700 gallons of oil this past year and got terrible DHW to boot!

 

The landord probably has the same comfort issues that you do then. Is his side still heated with a puking oversized oil-burner, or did he switch to gas on that side too?

A 700 gallon/year fuel use during a cooler than average heating season with an old oil boiler that was also heating your domestic hot water implies a design heat load of somewhere between 25-30,000 BTU/hr at most. So yes, the -105 was a pretty lousy choice, as it is for most homes. The ALP080 is a more appropriate boiler for 19 out of 20 single family houses in MA (and 99 out of 100 duplexes- even older uininsulated duplexes!)

If you can figure out a way air seal and insulate the place it's likely that your heat load would drop to the 15 K-BTU/hr range, at +8F (or whatever the 99% outside design temp is in Newton), which would be below even the min-fire output of the -105 even during the polar vortex event. Before insulating you'll probably burn something like 500-800 therms/year with the thing, which may cost about a grand a the high end at recent years' pricing. There isn't a quick financial return on it with heat loads that low, but it's worth insulating for comfort reasons alone.

Run the short-cycling test by dropping the programmed output temp to see where it really lives then report back. My gut tells me you probably have enough mass in the system that it isn't going to be too bad. Big old radiators have a distinct advantage over fin-tube baseboard when running low temps.

 

I understand the absurdity of the 105 as I stated earlier. Being a tenant I was a bystander to the decision making process. It was only after it was installed that I discovered this forum and want to learn to use what I have. I will run the test you outlined earlier. I don't believe you indicated how to determine the return water temperatures. I'm assuming that the display reads the supply temperature. Is there another screen that shows it or do I need special equipment to read it off the return pipe.

 

To get the output water temp, first hit the MODE button until it is in InFo mode, as indicated in the paragraph on page 51 of the manual. If it doesn't automatically then show a number (don't know if it does or doesn't, haven't used this one), hit the STEP button.

It should have a "1." in front of the temperature reading which indicates that it is displaying the output temperature.

Tap the "STEP" button again and it should have a "2." followed by a number, which is the temp of the return water that is entering the boiler.

Keep tapping it and it'll step through other valuable bits of info too, always preceded by the step number it is on, to indicate what the number on the display is indicating.

See figure 36 on page 53 of the manual.

Really, don't just use it for a pillow- read the whole programming section!

 

Sounds like you're on the right track. I started with 1 zone on the first floor (second floor unfinished) of my house with about 35 feet of Multipak80. After the first winter of short cycling I took all of that out and put in cast iron basebaord which works much better. With the max fan speed set to a little over the minimum I get about 2 cycles an hour during the winter (recently renovated home, Roxul in all cavities, all new windows/doors). Shoulder months are a little more. Since Dana was nice enough to include some technical direction above I will copy that down and make some adjustments this year to try to cut cycles down when it's not below freezing. From what I've seen I condense on all heating calls.

 

Sounds like the right tweaking will result in a majority of condensing heat runs without freezing me or smoking me out. Being a rental, I have no options with respect to changing radiation etc. All I can do is adjust the boiler settings. Since the DHW is set at 140, I assume there is no condensing option there because you need higher supply and return temps to heat the water. Since that only amounts to probably 15 minutes a day max of run time I won't worry about that.

 

The best you can do on the domestic hot water efficiency front is to insulate all of the potable near-tank plumbing to R4, including the cold-feed into the tank and any temperature/pressure relief outflow. The 5/8" wall closed cell stuff is about R4, but you may have to settle for the crummy R2 3/8" wall goods found at box stores. Insulating all of the hot water distribution plumbing to R4 would be worth it too.

The hydronic loop plumbing between the indirect & boiler could use R4 as well, but for potential high-temperature reasons it has to be rated for at least 180F, which most of the foamy stuff isn't. The 1" fiberglass stuff for steam pipes works, but it's expensive enough that the payoff won't be in just one season. The half-inch fiberglass stuff at box stores is overpriced and only R2-ish.

 

That's next on the to-do list.

 

It's a rental and the landlord is ok with you screwing with his boiler? If I was the landlord you would be looking for another place. His liability doesn't cover you screwing with things.

 

Tom, nobody is looking for landlord/tenant help. Let's stay focused on plumbing advice. He has the identical setup as me (newly installed also) and we are good friends experimenting with the boiler together. Thanks.

 

You are experimenting on expensive equipment that doesn't belong to you for one and for two you need a license to work on heating equipment especially if you don't own the house or the equipment. You screw that up and cause damage and you are liable.

 

Tom, nobody is screwing anything up except you for offering unwanted legal advice. Do you have a license to practice law? Didn't think so. Leave this thread for those who graciously share their PLUMBING knowledge, which has been very helpful.

 

Why are two non professionals screwing around with equipment they don't own?

 

I do have a license to install and survice gas piping and equipment. It's required and especially in Massachusetts it's required. What you are doing and asking advice to do is illegal. Had Dana and jadnashua realized that at the beginning I'm sure both would have shut you down. You are messing around with equipment that does not belong to you. The law in Massachusetts says clearly that you are not allowed to work on gas appliances without a proper license. Plain as that.