HTP Tankless for Radiant and Domestic Hot Water

_Mike_

I'm considering a recommendation to install a HTP propane on-demand system to heat 11 glycol-filled radiant circuits and a smaller baseboard circuit (separate zones) plus the domestic hot water. They are all the rage in my small town in NH , and the state offers an energy rebate to convert. My friends who have this brand (and this type of system in general) love them. Any thoughts, experience, or opinions on this brand or type of system in general?

Happy New Year!
Mike

Gordy

Model number?

_Mike_

UFTC-140

Ironman

Have you done a heat loss calculation like a Manual J?

_Mike_

*Gulp* what's that?

hot_rod

An innovative, well know brand, with plenty of track record in the high efficiency market.
As Bob mentioned, do a load calc to help you select the best size.

Ironman

_Mike_ said:

*Gulp* what's that?

It's a scientific heat loss calculation that determines the ACTUAL amount of heat your house needs. It's the foundation for sizing and designing everything in the system - including the boiler.

This isn't like buying a stove where you just pick the one you like.

Gordy

I see you are contemplating not fixing your existing boiler, and buying a new one?

_Mike_

> @Gordy said:
> I see you are contemplating not fixing your existing boiler, and buying a new one?

My plumber asked me to give him two options to price out when the distributors reopen tomorrow. I'm thinking option #1 is to fix gas valve on 17 year old boiler & replace indirect tank w/stainless steel tank as one guy suggested. and option #2 is the HTP system my plumber recommends. I know #1 is the less expensive option initially, and I am confident it will work since it met our demands before, but I am thinking #2 would pay off over 20 years. I have not yet discovered any disadvantages to the HTP system except higher initial cost.

I could potentially have all this work done on option #1 and the boiler goes in 5 years...

I'm thinking the mess on the flue could be resolved with a good service to the boiler - it has been a few years.

_Mike_

> @Ironman said:
> *Gulp* what's that?
>
>
> It's a scientific heat loss calculation that determines the ACTUAL amount of heat your house needs. It's the foundation for sizing and designing everything in the system - including the boiler.
>
> This isn't like buying a stove where you just pick the one you like.

I found a calculator online... I plugged in some rough numbers for my marginally-insulated 3,000 sf house with single pane Windows and got ~50,000 BTUs. Does that at least pass the giggle test? Sorry, I'm an amateur at this...

Ironman

I would say that's low. You're probably gonna be around 75 to 90k btus. There are a lot of variables. Those online calculators are about as reliable as politicians. They're definitely not scientific.

SlantFin has a heat loss calc program that's free and you can download. You've got to take measurements and input the info.

What's also important is know what type of radiation you have and how much output it's capable of.

I wouldn't recommend the combi version for a house your size. Look at using a properly sized UFT and a SuperStor indirect water heater.

_Mike_

Thanks - will take a look at Slant Fin... For what it's worth, 3 upstairs bedrooms are heated with baseboard electric

Ironman

_Mike_ said:

For what it's worth, 3 upstairs bedrooms are heated with baseboard electric

a lot of dollars wasted when you could do it with gas.

Gordy

Electric bills around my parts are like we are at 11.5 cents a kw after all fees.....

mikeg2015

If looking at propane you might also consider using an air to water heat pump or undersized geo with propane to supplement.

Baseboard electric radiant might still make sense for upstairs. Better zone control. Could use with heat pump in mild weather if you have AC.

Need to look at propane vs electric costs

Brewbeer

What are your domestic hot water requirements and incoming winter water temperature ?

_Mike_

Awesome feedback guys - I've been doing my heat loss calc (kind of guessing at some of the insulation questions) and found the following:

Whole house, including crawlspace: 76463 BTUs
Area heated with propane: 56,863 BTUs
Area heated with electric (3 bedrooms upstairs): 12,415 BTUs
Crawlspace heated to 32 degrees: 7,185 BTUs

We do have a wood stove and a fireplace, which probably increases the BTU's needed.

Electric cost: $0.196 per kWh
Propane cost: 2.799/gal

We only run the electric upstairs when we are home so that level of zone control seems to have worked well. One of the rooms is a guest room anyway and rarely gets used.

Groundwater temp is pretty chilly... probably 40 degrees coming out of the well.

Hot water needs: bathtub, shower, two bathroom sinks, kitchen sink, dishwasher, and laundry washer.

No A/C, it would rarely be needed.

_Mike_

Also, the radiant heat is 11 -filled plastic tubes under a wood subfloor with insulation between joists. Above the subfloor is a pine floor.

Jamie Hall

I might to the confusion... the odds of a tankless lasting 20 years for you are slim to none.

_Mike_

Jamie Hall said:

I might to the confusion... the odds of a tankless lasting 20 years for you are slim to none.

What would be more reasonable to assume? 10?

Gordy

The UFT is a combi.

Gordy

Depends on water quality. The boiler could last 20 years so long as it is maintained well.

Let's face it if your old boiler is 17 years old? The longevity may be a moot point in comparison of options.

Gordy

With the radiant emitter the modulation condensing boiler is the better option. The UFT is a fine boiler for the price point. Personally I like a tank style WH. At least you have a reserve if something goes wrong with the boiler. Tankless, and combis are sensitive to water quality on the domestic side.

hot_rod

In my area well water never drops below 50- 52 degrees for a 300' deep well. Unless you are storing it in a cold well house I'd guess yours would run about the same.

Most combis are spec for a 70 degree or more temperature rise so 50- 120° is right at what their output sheets show.

120F is a common DHW setting, most folks rarely bath above 102- 105. So even with 34° water you will get a hot shower with a 70° rise.

Really the designer and installer is the key to a successful installation, pretty much all the brands are about the same components and quality. Installers generally have a few brands they prefer and trust.

_Mike_

Here are some photos of my radiant system

hot_rod

If that is your radiant tube installation it is what is known as suspended tube method. The heat transfer is from the tube wall, to the air space- to the floor.

It needs to be well insulated below, have a few inches of air space above the insulation.

It is not one of the most efficient ways to transfer energy to a floor, and generally requires a higher operating temperature.

If you have under-performing areas, adding heat transfer plates will help the output.

Gordy

Yeah that radiant detail is lowest on the list for output, and highest on the list for hottest water temps needed.

Is it doing the job as is?

_Mike_

Gordy said:

Yeah that radiant detail is lowest on the list for output, and highest on the list for hottest water temps needed.

Is it doing the job as is?

Yes, current system does the job. House is plenty warm on the coldest days (but a little drafty due to single pane windows and marginal insulation). Hot water was never an issue either: 15 min after someone showers it is ready for the next person.

heathead

Mike,

Brewbeer hit the nail on the head with the tankless water heaters. Measure your cold faucet temp now. Is it coming in at about 36-42 degrees. The Boiler is rated for 77 degree rise with 3.3 or 4.8 Gallons per Min. output. Depends on model. When you raise the temperature of the water from say 36 to 130 rise of 94 degrees. That gives you less than 3.3 GPM or 4.8 GPM search for other threads on that, it will supply the hot water but will slow the delivery rating for the 3.3 GPM to say (just a guess 2.2 GPM)

The boiler being combi unit hot water and radiant The boiler will turn on and off every time you run hot water. Ask question about longevity of standard boiler vs combi unit.

The current boiler has bad gas valve, What is the story with fire, did something block the flue or did the draft inducer not work properly? Make sure that the safeties for draft inducer work before using boiler with replaced gas valve.

Questions for others on this site is indirect water heater vs combi unit. I think lots would think the indirect tank would be better option. Last longer lower moving parts no descaling of heat exchanger. Others thoughts

As has been said check gasket in top IE verify tank leak as other have said and not just top gasket. That tanks track was not as good as it should have been being Buderus . I think lots have failed around 10-14 years I could be wrong. If you don't have high clorides in the water the stainless steel indirect tanks should last a much longer time.

The heat loss for the structure is important, and should be done as not to oversize things, but the system is hooked up to under floor heat. That heat can only put out so many BTU's per square foot. one could size the boiler on the output of that, assuming you don't add more radiant heat to upper bedrooms. Can you take picture of the tube running under floor move some of the insulation out of the way. Is the tubing running through aluminum plates or just stapled to bottom of floor boards.

Others think the boiler is worth fixing the gas valve, Can't post prices but you could say to replace gas valve is % of new boiler replacement. The one point on the gas valve is that will get you running. Take some more pictures of piping because the zones should be mixed down from the boiler temp. I think the boiler will run down to 130 degrees without the propane condensing. The white powder on the exhaust flue is residue from boiler running a very low temp and starting to condense.

heathead

Question for others on this site with suspended tube and no transfer plates, what temp will the system run? What efficiency could one expect on the UTF combo boiler at that running temperature vs current Buderus Boiler? What are maintenance cost between the two to think about ? That should be a deciding factor based upon current gas usage for previous years. Thoughts ?

_Mike_

The fire on the gas valve was from a buddy showing me how to change a thermocouple... We're lucky more damage was not done...

Water temp measured at 41 degrees today. So to get it to 130-140 degrees would be a rise of 89-99 degrees. However, wouldn't the starting temp be the temperature of the glycol in the radiant tubes? Not the water coming in from the well? The water coming in from the well would rise from 41 degrees to 111, which seems like it would be OK for a shower.

Photo of radiant pipes posted above - no plates. An inch or two of space between tube and insulation. Tubes stapled to bottom of floor.

Ironman

No, the starting temp is what's coming from the well.

Let me recommend three things:
1. Find the best boiler pro that you can; he's 98% of the equation.
2. Install and indirect water heater ( SuperStor) with the UFT, not a combi unit.
3. Get good quality EXTRUDED aluminum plates installed (not beer can) on your floor. You'll be able to lower the water temp from 180* to 130* or less. That will make a huge difference in comfort and energy savings with a mod/con boiler. Look at the chart: 7 btus output per sq. ft. the way you are now vs. 18 btus with good plates.

_Mike_

Doesn't The indirect tank defeat the purpose of the uft on-demand system? Maybe they replace the tank now as it is leaking, then with the boiler goes replace with UFT

Gordy

I think you should fix what you have see how far it gets you. That indirect may be repairable.

_Mike_

I got the quote on the HTP plus baseboard for the crawlspace... Still waiting for price on repairing what I have but I think my estimate of half the cost was pretty good so I am leaning toward following the advice I've gotten in this forum to fix existing system. Guy at supplier said I could get another 10 years out of that boiler I have.

Ironman

Again, I'm not talking about the UFTC combi, I'm talking about the UFT heating only + an indirect.

Like this:



The indirect is the silver tank on the right. The boiler heats it.

_Mike_

Isn't that an on-demand boiler in the photo? I'm a novice, so I'm having a hard time understanding why the tank is still needed.

Gordy

No.

A tankless is for heating DHW only.
A combi does central heating, and DHW via a seperate heat exchanger in the same unit.
A. Boiler does Central heating, and can do DHW via an indirect.

The UFT comes in a boiler only, and a combi.

_Mike_

Gotcha! Thanks!