Water Heater or Boiler

giceman1337

What method do you use for heating your hydronic radiant heat and domestic hot water. Please comment as to why you chose that method (pro/con).

Zman

I think you need to include an option for boiler with indirect..

Steve_210

Boiler with indirect
But depends on the customers needs and budget

giceman1337

I meant for the "Combo Boiler for Hydronic and Domestic" to represent that. I wasn't sure the exact wording to use. Also can't figure out how to edit the poll.

Gordy

Depends on the demands, and wants of the owner. Some nice combos with greater tdrs that can manage lower heating loads better, and have the extra output for DHW.

I’d favor indirect, and boiler. Nice to have a reserve of hot water on hand if the boiler goes down.

A lot depends on water quality with combis on the domestic side hx. Maintenance , and longevity can be an issue.

Tankless has same concerns.

With indirect very high storage temps can decrease longevity. However you can leverage storage capacity with higher tank temps, and having a tempering valve for the fixtures.

What’s your situation?

giceman1337

I will have about 1200ft^2 in basement (likely Warmboard or Roth panels) and 1200ft^2 underfloor on main level with aluminum spreaders. I have forced air heating as well, so the radiant heat is to "take the chill out" of the floor. Rough estimate I made was <70K BTUs/hr for radiant.

The domestic needs are 3 bathrooms with showers. 2 adults and 2 kids.

Right now we have a crappy electric water heater that is 14 years old. Looking to replace water heater, at same time as installing radiant heating, so I'm wondering what's the best fit.

Gordy

You would want to run the radiant with forced staged to supplement the radiant IF needed, not both together.

Deffinetly do a heat loss calculation room by room before you start your project. It is the basis for creating the radiant heating design. Is this new construction? 70 k sounds high.

There is one advantage to a stand alone gas tank style water heater. That is if boiler goes down you will still have hot water. Made a lot less efficiently however.

giceman1337

I was wondering how to configure to the 2 thermostats. I have a thermostat on the main level for the forced air. I will have a thermostat in the basement for radiant heat. I may have an additional thermostat on the main level for the radiant heat. I also have a 2nd story which only heats with forced air. I do have a connected "smart home" hub system where I could wirelessly connect all the devices and provide some of the controls within the hub.

The 70K estimate was high. I was calculating 20 BTU/ft^2 * 2400 ft^2 = 48K BTU. Then I added in radiant back loss for the basement slab ~10% loss (2 BTU/ft^2) = 2.4KBTU. Then I just fudged the numbers to a much higher value. What I also computed, which I believe is adequate is 15 BTU/ft^2.

So I am probably closer to 40K - 50K BTU/hr for the 2400ft^2 of heating.

Ironman

@giceman1337
If you're trying to use a poll to determine the best choice for your situation, you're going about it all wrong. This is a scientific trade that requires dealing with facts - facts that can be somewhat different for each job site. Those facts are NOT derived from an opinion poll.

A heat loss calculation, actual job site conditions, viable methods of design and installation, and how much $$ is reasonably budgeted are all things that must be factored.

As far as personal experience and opinion go, I would almost always recommend a boiler + an indirect. And so would most every knowledgeable pro - under most circumstances. But that doesn't mean that's the correct choice for your application.

A combi unit is one that does both space and domestic heating in ONE appliance. A boiler + an indirect is NOT a combi; it's two appliances.

delta T

Where are you getting those heat loss numbers from? Not disagreeing with them, but just curious. Heat loss is not done on a per sq ft basis, but on the actual construction of the building, type of radiant system used, insulation under the slab, insulation on the edge of the slab (very important factor that many don't take into account) and air infiltration (usually your highest single source of heat loss).

As per your question, I always prefer a boiler with an indirect water heater. Least amount of maintenance, best efficiency (usually), and longest life (assuming a stainless steel indirect such as an HTP Superstor or a Lochinvar Squire.)

giceman1337

I got the heat loss numbers from a supplier. I realized I misinterpreted the numbers and extracted meaning from them that was incorrect. I'm a noob.

The specific numbers were
21000 BTU Heating - 15 BTU/ft^2 * 1400 (included unfinished areas in this math)
9087 BTU Radiant Back Loss - uninsulated 4" slab, 6" exterior wall R19 (1) and poured foundation below grade with foam insulation (3), finished ceiling.

I then just doubled this estimate for the main level.

Ironman

You need to do an ACTUAL SCIENTIFIC heat loss calc. It's the foundation for sizing and designing everything in the system. Guessing, assuming and quick square footage calculators are worthless and grossly inaccurate.

SlantFin has a free app that you can download and it will get you close enough - if you input the correct info and choose the correct construction data.

giceman1337

I have looked at a couple of the apps and I don't even understand the information they are asking for. Any help in input parameters would be greatly appreciated.

giceman1337

I think I figured out SlantFin. My data is pretty close to what I had before. I came out with 29698 BTU for my 1400 ft^2 basement. I need to work the main level.

Brewbeer

Are you heating with natural gas? If so, you can get a good heat loss estimate using your gas consumption.
A scientific room-by-room heat loss calculation in a spread sheet looks like the attached file. If you are handy with a tape measure and a spreadsheet, it's worth looking at.

giceman1337

My primary heat is forced air. The floor heating is supplemental to just have a warm floor under your feet.

The boiler and/or water heater will be natural gas.

Gordy

You should do radiant primary, and stage the forced air as supplemental IF the radiant can't cover the load. However you will not know this with out a heat loss for proper design.

You will not feel any benefit from the radiant using them together.
Saved the f/a for cooling......

Gordy

Over 29k for a basement seems high. Is this a walk out. Daylight? Especially if your previous construction detail is correct.

Mark Eatherton

Combo Boiler for Hydronic and Domestic

My actual preference would be a boiler (modcon) with a reverse indirect DHW heater. It keeps the boiler in the condensing mode, even when its doing DHW production.

ME

giceman1337

I have a walk-out basement. 6" framed walls with R19 on exposed wall. The other 3 walls are below grade poured concrete with rigid foam insulation and thermal reflective coating. The floor is 4" poured concrete slab with no insulation.

Jamie Hall

giceman1337 said:

... The floor is 4" poured concrete slab with no insulation.

Oh dear. That's too bad. You will be trying to heat an awful lot of dirt -- and possibly ground water -- that way...

giceman1337

A friend I know with a radiant system and a domestic hot water uses this system from Westinghouse. Anybody know anything about using these?

Otherwise I was looking at the Navien systems. Are these Combi systems different from a boiler and indirect?

Jamie Hall

Well... it seems to be a nice fancy high efficiency water heater anyway...

If it were mine to do, I'd use a nice mod/con for the radiant heat, and whatever I wanted for the domestic hot water. That way you are using the equipment for what it's intended.

giceman1337

(Sorry, I accidentally edited my previous post instead of posting new).

I need a good recommendation. My current water heater just died. What is a good boiler with indirect system to use? Very ironic since I was looking to replace it.

Gordy

Mod/con boiler, and indirect. Far better control than that....

Gordy

Look no farther than HTP, Lochinvar,many others well versed in hydronics, and DHW.

Search the board for Navien, combi, and water heater radiant woes.

giceman1337

Thanks guys.

Mod/con boiler

That looks like overkill for my needs. That seems like a commercial boiler.

I think I received a quote on an HTP EFT combi-boiler. Are Combi systems different than boiler w/ indirect?

giceman1337

One question I have always had on boilers and usage in the radiant flooring. The boiler produces water that is typically very hot (>150F), but the flooring will require relatively cool temps (100F). Does this harm the boiler to "over-supply" that much heat?

Gordy

A modulating condensing boiler can produce what your radiant floor needs easily. Actually the lower the supply water the better, it makes the boiler more efficient. A cast iron boiler would require a mixing valve to reduce the supply water temp to the radiant. It mixes some of the cooler return water with the supplied hotter water.

Gordy

If you really want to up scale DHW production efficiency. Go with a reverse indirect.

giceman1337

I feel like an idiot. I thought "mod/con" was a brand name. The first thing that showed up on Google was HTPs 6.5M BTU system.

Mod/con = Modulating condensing boiler

Gordy

Correct. Many different sizing slots. This is one of the reasons a heat load calc is very important.

giceman1337

What about the pro/con of Combi vs Indirect Water Heater?

Gordy

Pro takes up less space one unit does both.
For some with limited space, and lower DHW needs its the right choice.

Cons unless you get a high TDR ( turn down ratio) 10:1, 15:1 combi the unit has a very high btu input to make enough hot water instantaneously. Which translates to way more than necessary for CH (central heating).

Of your water supply is high in chlorides, and or hardness the domestic HX will require higher intervals of maintenance.

You will need to carefully analyze your DHW needs, expectations, and incoming water temps to decide if a combi is right for you. Don't expect to run dishwasher, clothes washer, and shower with a combi.

giceman1337

I completed my Heat Load using Slant/Fin App. Assuming I entered everything correctly, here's what I computed.

Heating needs:
Basement - 29698 BTU
Main Level - 28681 BTU

My DHW needs is 2 adults and 2 growing boys (8 & 6). I expect times of multiple showers occurring at the same time. I don't know about multiples showers + clothes + dishwasher (seems overkill).

My incoming water in Minnesota is quite cold. I think it listed average of 45F.

Gordy

I'm really not sure what you want to hear, or read on this.

giceman1337

I am just looking to gather as much information I can. I figured if I shared some of my information it may help guide the responses.

giceman1337

I don't know how to compute my DHW needs and size the boiler and/or Water Heater.

Gordy

The boiler would be sized for your heating needs as close as possible. Just under 60k (output) so an input of 80 k. probably a uft 80, Lochinvar wh 80, Lochinvar KHN 80, Weil McClain etc. this size will be sufficient for producing DHW for an indirect of 40 gal.

Many other choices. The ones I listed are 10:1 and 5:1 tdrs.

giceman1337

Thanks Gordy. So if I am understanding the indirect tank doesn't need to be as big as normal domestic water heater because the boiler will be able to continuously reheat the water within the indirect water heater?

Is 10:1 and 5:1 TDR the modulation efficiency of the mod/con? I assume higher is better.

hot_rod

Combo Boiler for Hydronic and Domestic

The main attractions to Combi units are the small footprint, and instantaneous DHW production.

The downside is they are often oversized to the heating load.

Some brands have the ability to limit fire rate on the heating mode and ramp delay to help reduce that cycling.

The Lochinvar Nobel, 110 which I have in my house can deliver 3 gpm or so on the DHW function and can be derated on the heating to 11,000. That would be a fairly good match up for your home.

I'd guess Minnesota water drops lower than 45. Milwaukee water temperatures can drop to about 37F in winter months where it is stored above ground.

We had a webinar back in December presented by Paul Rohrs from Lochinvar. It compared tank, tankless and comb pro and cons.

This slide shows the range of sizes, DHW production and min firing rate for SH mode.

Yes, if you have hard water you may be deliming yearly. It's a fairly simple task if you install service valves and buy a delime kit. Most homeowners can do the service. Plenty of You Tube videos on servicing tankless or combis.

Here is the link to the 1 hour webinar.

https://www.youtube.com/watch?v=ACRhtPUsJnE&amp;list=PLuuV0ELkYb5VE0I4evUZ30b5U78CRlRdg&amp;index=41