gravity hot water conversion

STEVEN MARKS

Installing a new gas fired cast iron boiler. Would yo size boiler by the heat loss only or add a little to the size to make up for the oversized piping and radiators.

2 choices

Peerless MIH5 109,000 net, 95,000 IBR

Peerless MIH6 136,000 net, 118,000 IBR

90,000 BTU/HR Heat loss

icesailor

Gas conversion

Personally would go with the larger of the two. The 95,000 Net IBR will do the job and will give you what it is rated for.

But in the world I live in, oil gives you a rated number. It is always the same BTU content per gallon of oil.

Nat. Gas is the perfect fuel. As long as the supplier can deliver gas at the rated pressure and the rated BTU content, on the coldest design day, you will be fine. If however, something happens and the gas pressure is lower due to unanticipated demand due to weather conditions, you will not be covered. You will rue the day that you picked the smaller one.

But that is my opinion and others will argue that it never happens. Except when it does happen.

I was at a Veissmann class and a guy asked about the ability of a Vitodens 200 being able to correct for lower gas pressures. The instructor said that the burner brain could adjust down to below ..045" but wouldn't give the rated output. The guy said that in certain areas around New York City, it goes that low when it really gets cold.

Just my opinion.If I did the install and you were cold, what could I say?

How are you going to connect the high mass system to the new boiler? 

STEVEN MARKS

piping

Thanks for the input. I was planning on piping primary/secondary with a bypass on the boiler loop to try and keep the boiler from condensing. I was also planning on a Taco outdoor reset system.

icesailor

Gravity Conversion

Check out the Taco I Series 4-way mixer. You get Primary/Secondary and outdoor reset PLUS boiler protection. They are the nuts. It modulates the system and resets the system water. They are the perfect set-up. I just did one on a gravity system that was one zone on two floors with 4" supply and return. The new boiler was over pumping the system and so on. They are about to call my flight. If you are interested, I'll tell you more.

NYplumber

please, lets hear more

Icesailor, if you can, explain more. I have used four way valves to correct others mistakes on long runs where there was not enough btus in the water to supply heat to the emitters.



As much as you can explain, the more I'm willing to read

JohnNY

Gravity

I find that constant circulation via an outdoor reset device like a tekmar 260 provides the most even distribution.

icesailor

"I" Series Mixers:

This valve will do it all for you.  I used the 4-Way. It comes with either outdoor reset to the boiler or reset the valve to control the system. That's what I used. It has two DIP switch settings. 120 degrees for gas boilers or 140 degrees to protect oil boilers.



http://www.taco-hvac.com/en/products/i%20Series%3Csup%3E%26reg%3B%3C/sup%3E%20Mixing%20Valves/products.html?current_category=184



I turned the boiler on at a cold start. I have no idea how much water is in the system. In 15 minutes, all the returns were coming back at the same temperature. I put thermometers on the system supply and return. In that 15 minute period, the system settled down and I had a 20 degree delta T in the system while the boiler ran on the high limit it had been set at, 160 degrees.

What has been said about primary/secondary piping will overcome gross mismatching of pumping is true in spades. I could get adequate flow in the system with the pump set on #1, the slowest speed.

If you had a high mass system with a low mass boiler, this valve will solve a lot of problems. It comes with the sensors and all.

Check it out.

icesailor

Hot water to emitters:

Did you have not enough hot water to the emitters because the boiler was too small or because the temperature leaving the boiler was out of control?

Did your 4-way valve have sensors?

STEVEN MARKS

low limit

What if I instaled alow limit control that would shut of the boiler/primary pump whenever the boiler temp was below 125 F. When the boiler temp rises above 125 degrees the pump would start and inject hot water into the secondary loop.

I also found the Weil McClean CGA 5 has a DOE of 117,000 and IBR of 102,000. I think this boiler would be a good fit for the 90,000 BTU/HR heat loss.

kcopp

The boilers...

you have mentioned are OK..... but did you ever consider upgrading to a mod/ Con? The outdoor reset function is built in and the concern for too low a water temp is not an issue... Figuring the add-ons in the CGa/ MI boiler you may be closer to a Mod/Con price... especially if the local utility has a rebate.... kpc

icesailor

Conversions:

I did this on an existing gravity system that had a 10 YO +/- Peerless boiler with an indirect. It is cold start. The owner, and most all customers I run into will not spring for a new boiler and such. It is just too much money at this time.

This 4-way valve gave me boiler protection, outdoor reset and total temperature control of the system. The system was extremely over pumped with a Taco 010. I left that as the boiler pump. I installed a much smaller system pump that does the job better than before. You don't need 40 GPM in a 4 GPM system. You can install it in a day. You can connect the primary pump wiring to the secondary pump so that they pump together. The supplied system sensors can be connected to make that part of the valve work. If you supply it with 24 volts, and connect the low voltage outdoor sensor, it is running.

I'd personally rather offer this to someone who might spend the money on it and I get something for my time than offer toots and whistles and get nothing because of the cost.  If you have an old system, with an old boiler, you could offer this as the first stage of an improvement/upgrade. Connect the supply and return together on the old boiler, make your closely spaced tee connections as recommended, and when the customer sees that you gave them something truly awesome and they save money too, and you have a potential customer for life. When they get the cash for the new boiler, you just connect it in place of the old boiler on the boiler loop side. Piece of cake.

I've seen a lot of old gravity/pumped systems where a new radiator was installed on a long run off the system. It never gets hot as fast as the rest of the system so there is a cold room. When you do this, the long pumping times where the water really flows into the whole system, this cold return would usually be resolved or at least improved. Gravity systems weren't designed to have high capacity flow to work properly. They depended on low flow in big pipes to get the GPM proper. A lot don't understand this.

The only time I make money is when I sell something. If I don't offer what someone needs and can afford, I don't make any money.

Think about it.

icesailor

Low Limits:

Not to be redundant, but you don't need to worry about a low limit because the boiler protection lets the boiler heat up really quickly and as it gets to the set point, allows more cold water to enter the boiler, stopping condensation. A far better way than cold shocking the boiler. I'm big on low limits. With this, it isn't a problem.

So far.

NYplumber

long loop

Too many emitters in a row.

Jason_13

Mod/con

I usually would rather see a cast iron boiler in high temp systems but this is probably going to be a low temp system. You did the heat loss now measure the radiation and divide the heat loss by the sq ft of radiation and that gives you the btu's per sq ft of radiation. Use a radiation chart and determine the high water temp on the ODR control. My guess is the max water temp you will need is 140f or less.