New Boiler/Installer....Some Help Please

FloMo201

Hello All,

This is my first post but I have spent a day or so reading. I wish i had known about this site sooner.

I want to upgrade my boiler (hot water system) before this winter and after speaking to 4 installers in my area have narrowed it to 2 of the 4. First I would like to say that all 4 quoted the same size boiler at 175k BTU...which is the size of my current equipment. All 4 cited that the house is about 30 years old and the current boiler is original....they all said the boiler would have been sized for the house as it was new construction at the time. The house is about 3k sq feet with 4 heating zones.

The biggest difference between the 2 installers seems to be the piping. They both quoted a Peerless MI6. Because of this site I was able to confirm that both pipe their boilers with the pump on the supply side feeding away from the expansion tank, which they pointed out is how my current boiler is piped. They are both quoting new feed, backflow, spirovent, and zone valves.

Installer #1 is planning on using a primary/secondary set up. Not knowing what this is, he tells me it will benefit the boiler and protect it from cold water return. My googling is what lead to this site .

Installer #2 has no mention of this in his quote. He told me its not necessary and my current boiler is not piped that way.

Between the 2, I liked Installer #1 better. Privately owned business where I spoke directly to the owner and he seemed knowledgeable. I was also able to verify his licenses, which I was unable to do with the larger outfit...but they are popular in the area.

Your thoughts on this primary/secondary set up? I am paying for something that i don't need or is there really a benefit here? Are there questions I should be asking the installer about the set up?

Obviously there is a price diff, which I know I cant discuss. I just want to make sure I am not being sold something I don't need.

I am trying to go as simply as possible given all the manufacturing nightmares that are going on with both overseas manufacturing and covid causing manufacturing delays.

For sizing....I have learned about this heat loss that is done. Does it require someone spending alot of time in my house throughout my entire house? Due to covid, I am limiting people entering my home. But after reading here, I would like to discuss sizing with Installer #1. How do I do that without making him feel as if I am stepping on his toes?

Thank you for your help, Flo.

Robert O'Brien

Keep looking, 175K isn't the number.

Jamie Hall

On the heat loss. If you go to the bottom of this web page: https://www.slantfin.com/slantfin-heat-loss-calculator/ you will find a well hidden "click here" which will allow you to do your own heat loss. You do need to know something about how your house is built, but that's not a problem. It's easy and rather fun to do -- and the calculator is astoundingly accurate, or at least I've found it to be.

Try it.

As to primary/secondary piping -- there are some real benefits, mostly in that you can more easily run the best temperature for the radiation, and can run the pump for the radiation almost continuously if the mixing valve is driven by outside temperature (called outdoor reset) which gives more even comfort. However... it's much less of a benefit without that, and with big radiators or relatively short baseboards you may not gain anything at all. Hard to say.

Ironman

The the main concern that I see is that both are sizing the new boiler from the size of the old one. That’s a huge error. What if the old one was sized wrong (very likely)? Then they’re just repeating the original mistake. If the house has had any upgrades like new windows, more insulation, etc, then the heat loss is decreased and a smaller boiler may be needed. Also, new boilers are more efficient and don’t waste as much heat up the chimney. So a smaller one may be sufficient from that standpoint alone.

IDK of a house built in the last 30 years that needs more than 25 btus per square foot. Even if you needed 30 btus per square foot, that would only be 90k btus needed on the coldest night of the year.

What type of radiation do you have? Fin tube baseboards? If so, you can figure an output of about 500 btus per linear foot of ELEMENT. Measure them and see what total number you get. For instance: if you have 200 feet of element, then you’d have 100k btus output capacity from your radiation. It would make no sense to install a boiler with higher OUTPUT than that since that’s all that the radiation could emit.

A heat loss calculation needs to be done and compared to the radiation survey mentioned above. A good contractor should be willing to do this, but may have to charge for it.

You can download a free app from Slant/Fin and do one yourself and then you’ll know the ACTUAL heat loss of your house and what size you need. As long as you enter the correct data, you’ll get an accurate estimate.

Again, you only need that many btus on the coldest night of the year (0-10*). At 35-40*, you only need 1/2 that amount. 

KC_Jones

Roughly speaking, I'd suggest 175k is probably close to if not double the size you actually need. Do your own heat loss, then find someone who is willing to do one for the installation. Doing your own is a good reality check for what an installer is doing. In your case it will be a major eye opener for what you currently have, as well as what they are proposing. Bigger isn't better.

As far as stepping on their toes, they are planning on doing something incorrectly, at that point I usually don't worry about their delicate sensibilities since they seem to be ok wasting my money.

FloMo201

Thank you everyone. The boiler is connected to baseboard throughout the house. I will check out the link to the calculator and/or measure the baseboard..seems easy enough for me to do.

I will also discuss a heat loss with Installer #1. You are all right...I shouldn't be worried about stepping on toes.

Lets assume he works with me and resizes the boiler....am I wasting money on the primary/secondary thing, or does it actually help the boiler?

Thank you again for your help, Flo

Ironman

P/S piping is a good thing to help maintain proper flow through the boiler, but not really necessary for a cast iron boiler connected to fintube since the volume of cool water returning to the boiler is low and not sustained for very long.

Personally, I'd be considering a mod/con which would probably be more efficient depending upon your locale and some other factors.

Is your present chimney masonry and if so, is it on an outside wall?

STEAM DOCTOR

Hi. 50 or so BTU per square is a bit much. Don't see much benefit to a mod/con on a relatively small system. Especially one that's using fin tube baseboard. Cast iron boiler will typically outlast modcon by factor of 2 or 3. Simple machine with not to many parts to go wrong. Just my 2cents.

FloMo201

Thank you all again for the input. I am purposely choosing to stay with an old school cast iron boiler. i really don't want to deal with the added complexity these mod/con/condensing/whatever they do equipment does to save some money. In the long run do ya ever really save anything?? I am looking for simplicity and comfort.

I used that calculator and I got approx 106k as my value. I will be having that sizing conversation with both installers.

Again...i appreciate the help. i really wish i found this site sooner.

Flo

Ironman

Even the cast iron ones are not that simple anymore; the weather compensated controls which are now mandated are almost as complex and expensive as those on mod/cons.

Please answer my previous question about the type of chimney that you have. You may not be able to connect a new 80%+ cast iron boiler to a chimney where the previous 65% one was. A lot of installers don't know this and do it and then the problems arise: flue gas condensation, poor or improper drafting, CO poisoning, etc.

mattmia2

How do you make domestic hot water? Is it from this boiler or is it a separate appliance?

The primary-secondary may also let you run your supply water temp at a lower temp for more even heat if your emitters are oversized. It also has some benefits if you are making domestic hot water with an indirect water heater off of the boiler.

FloMo201

Hi,

Okay I understand...chimney is a prefab...vinyl sided box with flue pipe in it. My domestic hot water is from a separate hot water heater, gas, and also connected to the same flue pipe venting that boiler uses. Each has its own damper before the flue pipe comes together into a larger pipe and up the chimney chase.

Thank you again, Flo

EBEBRATT-Ed

@FloMo201

using the Slant Fin app will give you an accurate heat loss. Once you have a btu # from the baseboard or the Slant Fin app you pick a boiler that will produce the btus you need as a "Net" rating.

Realize the the net rating (the heat output you need) is different from the input rating of the boiler by as much as 35% depending on the boiler you pick.

So for instance if the boiler quoted above is 175,000 input the output (net rating) is probably around 120,000

If It was me I would use PS piping

Steamhead

Fire him if you haven't already. There's no excuse for that behavior.

psb75

FloMo201 you are now "armed" with incontrovertible knowledge from this website. A properly done heatloss spreadsheet, or a simple "tally" of total radiation is hard to dispute (but some will still try-- by hemming and hawing). A properly sized boiler is a shockingly 'rare beast' in our built-world. If a qualified mechanic is on-site (a Godsend?) installing a new, right-sized boiler--why not have that person do a little near-boiler re-plumbing and have your boiler set-up with all of the benefits of primary/secondary principles? Seriously. Fo' "mo-bettah FLO."

FloMo201

Thanks again everyone. I will certainly discuss sizing with both. Hopefully I don't have to start over with a new installer.

Regarding Ironman's question on my chimney. Is there anything that I should be addressing here? My chimney is one of those boxes, vinyl sided....pre-fab I believe they are called, which I assume has a flue vent pipe inside.

Flo

EBEBRATT-Ed

@FloMo201

Probably not a bad Idea to call in a certified chimney sweep and have them check the flue out

FloMo201

@EBEBRATT-Ed , I was already planning on doing that. Earlier you had mentioned that the new equipment should come close to the heat loss value. In my calc I came to approx 106k. Looking on Peerless' website, the MI06 has an input of 175, output of 143 and a Net Water of 124.

Is it the net water value that I want to match up closely to my 106k heat loss calc?? Which sounds like the MI05 is the better choice at 140 input, 115 output, and 100 net water. Do i have that correct??

Thank you again!! Flo

Alan (California Radiant) Forbes

Here on HeatingHelp, we are always talking about following piping diagrams and instructions in the boiler's installation manual. For some reason, Peerless doesn't mention primary-secondary piping; only direct piping is shown. Maybe they are confident they have enough mass to overcome micro zoning problems, but flue gas condensation in radiant heating applications would be troublesome.

Primary-secondary piping has more advantages than disadvantages and is worth the extra time, effort and cost for any application: radiators, baseboard, fan coils, radiant............

Jamie Hall

FloMo201 said:

@EBEBRATT-Ed , I was already planning on doing that. Earlier you had mentioned that the new equipment should come close to the heat loss value. In my calc I came to approx 106k. Looking on Peerless' website, the MI06 has an input of 175, output of 143 and a Net Water of 124.

Is it the net water value that I want to match up closely to my 106k heat loss calc?? Which sounds like the MI05 is the better choice at 140 input, 115 output, and 100 net water. Do i have that correct??

Thank you again!! Flo

I'm not @EBEBRATT-Ed -- far from it! -- but I'd say yes.

Robert_25

Flo - what is your general location?  What did you use for design temperatures in your calculations?

I live in a 3000 sq ft house built in 1910 on the Canadian border.  Blown in insulation, new windows, baseboard heat...I very rarely see a heating load over 50,000 BTUs per hr.

FloMo201

Thank you all again. You all are super helpful!

@Robert_25 , I am in the mid hudson valley (NY). The house is almost 30 years old. Andersen windows/doors so I chose double pane, its frame construction so I used 3" insulation for walls and 6" for attic (both guesses). For temperature, I used 0 outside and 70 inside.

Regards, Flo

Robert_25

I would expect your house to have twice that amount of insulation, but it would be best to check.

EBEBRATT-Ed

@FloMo201

I agree with @Jamie Hall looks to me like the smaller boiler will be fine. As for you insulation guess I think your right on a 30 year old house would generally have 3 in the walls and 6 in the ceiling.

I also agree with @Alan (California Radiant) Forbes

primary secondary isn't always required but for a few extra fittings and an extra pump it is good to have and you will always have the correct flow through the boiler.

Now that you have the right size boiler the savings will pay for the PS piping.


Now, to double check measure the footage of baseboard you have and multiply that (the finned element only footage) x 500btus/foot that @Ironman mentioned

Ironman

At 36 btus per square foot on a 30 year old house, I’d say your calculation is still very high.
I use the same design temp for houses up in the mountains near me. Even with an old leaky farm house, I’ve never seen one that needed more than 32 btus per square foot.

Remember, you only need that many btus on the coldest night of the year and then only for a few hours. Any other time the boiler is over-sized for the load.

JakeCK

With design conditions existing for such a short window, I would think one would be better off undersizing their heating system and installing a backup source for those cold nights? Something like a gas log set, which is what I have.

Worst case scenario you wake up and its a bit chilly.

Jamie Hall

Actually I expect that for a 30 year old house in your area, @FloMo201 , your guesses as to insulation are pretty good -- unless it was a real Cadillac job. Nominal 2x4 walls -- 3" insulation. You might have more the 6" in the attic, though I'll bet not unless some has been added.

Id go with your numbers...

psb75

2 x 4 walls in a 30-yr.-old house? 1991-- that is well after the 1973 Arab oil embargo Jamie.
I suspect more insulation and better air sealing than she's assumed. Easy to add attic cellulose though.

Hot_water_fan

Another way to figure heat loss is to look at the historical consumption compared to historical heating degree days.
Dana's method is easy to follow:
https://www.greenbuildingadvisor.com/article/out-with-the-old-in-with-the-new

Basically, the idea is that you rely on the gas meter since that captures reality.

mattmia2

psb75 said:

2 x 4 walls in a 30-yr.-old house? 1991-- that is well after the 1973 Arab oil embargo Jamie.
I suspect more insulation and better air sealing than she's assumed. Easy to add attic cellulose though.

But contractors are cheap so many put in as little insulation as possible. It could be well insulated, it could be next to nothing. The addition my parents had built in the late 80's has 2x6 walls spec'd for more insulation but when I looked in the attic 20 years later while replacing the roof I found that there was only like 6" in the inaccessible attic.

Unless you look you really won't know. The walls sometimes you can look in around outlet boxes. The ceiling hopefully you have some attic access.

psb75

Another way to figure heat loss is to look at the historical consumption compared to historical heating degree days.
Dana's method is easy to follow:
https://www.greenbuildingadvisor.com/article/out-with-the-old-in-with-the-new

Basically, the idea is that you rely on the gas meter since that captures reality


Correlating the gas bills/usage with the heating degree days DOESN'T account for an aging, inefficient boiler sending lots of BTU'S up the stack. Doing a proper heat-loss calc. is still the "Gold Standard."

Hot_water_fan

@psb75 I mean you discount the heat loss by the boiler efficiency of course, so it does.

tim smith

I still didnt see anywhere what size of house this is???? It could be a 5000 sftr or more. May or may not need that size boiler. Of course I agree with no one sizing properly, it is a shot in the dark.

Canucker

tim smith said:

I still didnt see anywhere what size of house this is???? It could be a 5000 sftr or more. May or may not need that size boiler. Of course I agree with no one sizing properly, it is a shot in the dark.

First post, 3000 sq ft