Boiler vs. High Eff Water Heater for radiant system

Dave_4

With high humidity winters, there is lots of free heat to be gotten out of dehumidification, right out of the high latent heat content of foggy air. Air source heat pumps add extra punch in places such as rainy Seattle.

Of course, I don't know at all how your place compares, in view of the rust you mention, I simply imagine all the Salt Lake vistas you must enjoy.

Steam systems can look very rusty on the outside (just because of their advanced age, and 65 is nothing) Usually a nice paint job and adding insulation covers up all the cosmetic stuff. At the same time, the inside of steam pipes remain eternally clean and brand-new-like while the returns in some instances do get to accumulate a lot of crud.

Crud that often ends up in the boiler (with neglected maintenance). Thus, new boilers from time to time are necessary. Indeed, boiler for boiler, there is a small difference in what these appliances do, but home heating doesn't stop there: consider the whole system; steam has all the attributes that give the glowing radiators the highest thermal efficiency.

That's where the creepy crawly steamy bugs live. We can all be Teetotalers when it comes to drinking the boiler water.

Thanks Alex, for enjoying this site - I most certainly do so myself.

Unknown

Use a boiler or high-eff water heater for a radiant system?

We anticipate replacing our steam heat system with a staple-up radiant retrofit. A major divide in companies we have talked to is using a boiler or (Polaris) high-efficiency water heater. Any input? Thanks.

Mike T., Swampeast MO

Sounds like you're dealing with internet-based, primarily DIY, "it's so easy" radiant sites. Be very, very wary!!

In a house old enough to have steam heat, there's a good chance that radiant floors of any sort will be insufficient to meet the load in some areas and depending on the system used (1 x 3/4" tube per joist bay with "flashing" type "plates" is common) may prove inadequate everywhere--floors in old houses are often quite thick and multi-layered...

"Water heaters" (where allowed) do certainly have a place in modern hydronic space heating, but in general only when the load is so small that a comparable, true "boiler" is significantly oversized.

And by the way, I would personally NEVER consider a heating system that combines space and domestic hot water heating in the same water.

hot_rod

The best first step

would be a room by room heat load calculation. Have a contractor help you or try on of the free calculators available here.

With those numbers you will be able to decide if a radiant floor system will "do the job" The calculation will tell you how many BTU's per square foot you require for each room.

A radiant floor could possibly give you as much as 25- 30 BTU/ ft. If the room requires more you may need supplemental heat. Floor coverings need to be considered also. Carpet and pad will put a hurt on radiant floor output.

The word boiler is slowly disappering from the radiant industry. Many new condensing heaters are showing up on the market that are ideal for low temperature radiant systems.

If you use a tank type like you mentioned, be sure the domestic water is seperated from the heating water. A heat exchanger may be needed.

If you work with a local contractor they could do a site visit to suggest the best equipment, safe venting, and possible upgrades to the home to save energy.

hot rod

Unknown

Two posts, each reflecting one side of the issue! It is confusing. It does seem that the new generation of water heaters, ie. Polaris, are well suited to radiant floor heating, mostly because of the temperature of water they excel in making is about the right temp for floors.

Slant/Fin heat loss calc: Total 48,000 BTUs/hr. The radiant floor calculator indicated the heat load could be met in all of the rooms.

Unfortunately, I could not find any local contractors to help with these issues. Also, the change in heat source is only possible with sweat equity.

The mix of DHW and radiant has concerned us, being biologists. Seems like bad stuff could start growing in all that tubing. Heat exchanger, or instant hot water heater for DHW? Tax credits practically give instants away.


Thanks for the input!

hot_rod

being biologists

maybe you could convince the folks selling those combined radiant/ DHW systems of the dangers

It seems sometimes low cost trumps the public safety with regard to combined systems.

Sounds like you are off to a good start with your project. Send pics as you go.

hot rod

[Deleted User]

You have good reason to be concerned...

The combination system COULD hurt you, or worse. A water heater turned too low almost killed me from Legionairres Disease.

http://www.contractormag.com/articles/column.cfm?columnid=645

ME

Jeff Lawrence_25

Where

Are you Alex, What part of the country?

Alex_13

To save energy, some advocate turning water heaters down to 120 F, and Mg and Ca precipitate out around 140 F. Sounds like the ideal water temp for any domestic water heater is 135 - 140.

For microbial growth, it also seems the dozens of feet of hot water pipe from the water heater to the taps is the ideal incubator as well. My brother-in-law is a wastewater engineer, and pointed out rightly that this is the reason why it is a bad idea to use hot water for anything but washing.

We are located in Logan, UT. Hard water and hard winters (but they sure seem to be getting milder).

Will a modulating, condensing boiler last 3X as long as a modulating, condensing SS water heater? I have perused postings here enough to know that cheap is not the same as inexpensive.

Have a great day.

Unknown

The polaris is not "new generation". it's a dinosaur. If you run it hot enough to be safe as a DHW source you don't condense, and if you run it cool enough to condense you fry out your igniters. I do not believe its energy claims, plus they are pretty loud.

The newer Phoenix water heater seems to have fixed some issues the other Voyager had, and if I were going to use a tank heater I would go that route. But then we still have the 140 tank temp limiting condensation... so I could see an arguement against that.

Part of this depends in part on what temperatures your radiant system needs. In a staple up retrofit, unless you are using heavy gauge plates and/or you have a very low heat loss, it is unlikely you'll be able to run the tank temperature low, even if it's dedicated for heating only.

With a mod/con and indirect tank, the tank can be kept hot, the boiler can fire hot to satisfy the DHW tank, and the boiler can run at a lower, variable water temperature based on the heat load for the radiant. This is, IMHO, a better solution IN MOST CASES. Not all, but most.

Joe Brix

How about a Combi-cor

combo WH from Bradford-White? Not condensing but you could probably run it at a low enough temp. Probably a little less then a Polaris and it will only last 10-15 years tops, but maybe it's more cost effective then a pricier mod/con.

ALH_4

Water Heaters

Inhalation is also a danger with Legionella. Ideally, the water heater is 140°F or hotter with point-of-use tempering valves at each fixture.

It sounds like the budget is relatively tight. For the lowest cost option, the Bradford White Combi2 that Joe mentioned is ok, but your heat load is reaching the point where a modulating condensing boiler is appropriate, though it sounds like it is not in the budget. Some of the low cost condensing equipment has a reputation for requiring more maintenance and repairs than its more expensive counterparts. Service calls will negate any financial benefit from high efficiency combustion (and then some) pretty quickly.

If using a combination heating/DHW appliance, the Combi2 is the best design in my opinion. It provides separation of the heating and domestic water, and it does so without the need for an external heat exchanger.

Dave_4

Sanitized scheme

And at steam hot temperatures all the bugs are fried - the ultimate in safety.

Dear Alex, is there any really valid reason for abandoning the steam system? Nothing new exists that delivers the performance as efficiently as steam does, plus steam maintenance is way cheaper than any rip out.

All that said, I think it exciting to install a perfectly new radiant floor system while keeping all of the steam in operation, for the sake of design failure redundancy alone, and also for the sake of following the weather curves thrown at you by nasty clouds, all that with the precision of a pro player.

Thus, a tiny output floor heat gives you base heat with little risks of expensive overheating, while morning steam wakes you up while it plugs the night time heat losses.

This way, not having to rely for life on radiant floor heat, you can allow yourself to go low temp, super low temp, as in hot water delivered to you by a heat pump - here, there is much energy savings to be gotten... all found in the magic of phase change heat transportation such as that of a heat pump cycle and of the good old home heating steam system.



Is AC a need you currently envision? Likewise, do you have very humid winters?

Alex_13

I suppose the reason (perhaps not valid) is the system is 65+ years old, and instead of a boiler (one bid from a trusted contractor was 7.5 K), we thought a new system for ~10K would then outlive the house. Higher efficiency, all-new system, and nice, warm floors were the compelling reasons for looking at DIY radiant.

Perhaps keeping the old system alive with a new boiler makes sense, but it sure seems like its rusting fast, and steam boilers don't have the highest efficiency.

It is great to have a clearinghouse of information like this, even if there are still some subjects that are, well, subjective. One bid for equipment only quoted a Munchkin boiler with indirect DHW tank - what is the perceived value of a Munchkin boiler compared to other high-efficiency models?

As for AC, Christian, RH hovers around 15% during the cooling season even in northern Utah, and a swamp cooler works wonders, especially for the dried-out sinuses. Our winters are rather humid, however, with snow sticking for most winter months.

ALH_4

steam

Christian just brought it back to the heart of the matter. For some reason I assumed you were switching primarily because you wanted radiant floors.

Unless it is in terrible shape, your best investment would very likely be to rehab the steam system and invest money in reducing the heat loss of the house, unless that has already been done. You might buy The Lost Art of Steam Heating at the Online Store above. It is an excellent description of the operation of steam heating systems. Once you have read through it, you can make a more informed decision about yours.

Why does it seem like the steam system is rusting fast? It may take some re-piping to revitalize the steam system. You might even add some thermostatic radiator valves to reduce the temperature of some zones and save some energy.