Boiler sizing and make for propane?

TAG

Rebuilding an old stone house (gutted). Getting lots of conflicting information. The heat loss is coming in around 52k ... I'm getting various recommendations for both sizing and make. One contractor is recommending a Viessmann 200 telling me they are the best with propane (only choice of fuel) .. other are saying to stay away and recommending Bosch/ Buderus. The house is around 3k SF (spray foam) -- 2 baths (no tubs). Initially, a weekend house --eventually full time. Sizing for boiler is all over the place -- 67k to 110k BTU. The guy recommending the Viessmann says 67K with a 50g indirect .... others say 110k w/ 40 gallon. House will have heated slabs and Warmboard. Ducted AC (Actually HP). I'm a bit worried about the hot water w/ 67k. House has a well in PA .. so the incoming is cold.

I'm not a newbie when it comes to all of this except the condensing boilers. Have done numerous personal houses with radiant/panels/runtal/warmboard and indirect HW. I did a Eccomatic Buderus Cast Iron boiler w/ Buderus indirect back in the early 90's (actually went to one of DH's seminars and got the books) --- just copied that system for all the others. The smallest being 118k boiler w/ 40g indirect. Seems the CI boiler w/ radiant is a dead duck -- except oil.

Is there really one boiler better with propane ....... and should I worry about only 67k into the indirect? I get that a typical water heater is only about 30k .. but they run out.

Thanks for any help -- I'm a long term lurker.

Ironman

Has a SCIENTIFIC heat loss been done like a manual J? That's what should be determining the boiler size. Don't upsize for the indirect; increase the indirects size if more domestic is needed (probably isn't).

I don't see where any particular boiler runs better on LP.

EBEBRATT-Ed

They will all run propane. Viessmann is usually looked at as the top of the line and also most $$$. Others will disagree.

An old stone house with 52k. I am not doubting it but you need to make sure your heat loss is accurate. You could use the Slant fin app and run it as a check.

I agree with @Ironman an accurate heat loss, don't upsize for the indirects (the boiler you select will probably be larger than your load anyhow) and the boiler rating will include the standard 1.15 pick up factor

Size the indirect base on the # of people in the house. I would think 40 gallon minimum, a 50 is a reasonable choice with two bathrooms

TAG

An engineering firm did one of the early calculations ...builders HVAC contractor was paid to do another using Wrightsoft. Have no idea how the first was done. It was based on 10/70 -- 60 degree difference. I think the engineer was 52K the second was 54k

It's big open space -- all spray foam ... new windows. The upsizing with others was for the hot water production .... when I asked the guy using the Viessmann 67KBTU .. he said if I was concerned about DHW production to just get the bigger indirect tank (going from 40g to 50g) .. the standby loss is small (most likely accurate).

Others just factored the SF and upsized the boiler -- I think the next Viessman is around 100k .. same with the Bosch.

For the most part the house will only have two people --- but we often invite guests ... so it's typical to have both bathrooms going on a weekend when both couples would be getting ready.

I'm installing ductwork and a mini split in one of the odd spaces for cooling -- They will be heat pumps so there will be some additional BTU's available.

bob eck

Boiler needs to be sized to meet heating load.
40 or 50 gallon indirect should be big enough. Store water at 140 - 150 degrees F and mix down to 120 degree F going out to your faucets.
Boiler needs to be sized right for heating load, piped in correctly, needs to be vented correctly, water going into the system needs to be checked and treated correctly, boiler needs to be set up with testing equipment, control on the boiler needs to be set up.
You the home owner is responsible for yearly maintenance.
Maintenance - maintenance - maintenance

You can buy the best high efficiency boiler on the market and If not installed correctly and not maintained yearly your boiler and indirect water heater can live a short life and give you many problems.

Where in PA are you located at?

TAG

The property is in northern Bucks County --

sunlight33

Have you considered 200-W B2HA with 19-100 (or 19-125) kBUT/hr modulation?

Ironman

What type of radiation do you have? Baseboards may require 180*+ on the coldest night of the year (design temp).

Viessman is a great product, but the manufacture limits that model to 167* SWT. That may not be hot enough depending upon your radiation's output.

Was an EDR (radiation) survey done?

Gordy

Is it all radiant?

I’d stick to the size matching the heat loss as others have stated.

You could go with a 10:1 tdr mod/con like a HTP uft, or a lochinvar. Gives you a lower end modulation, and you can lock out the upper end modulation so it gives a bit more breathing room on sizing.

Are you zoning? How many zones if so? Are zones ample size to reduce short cycling?

A uft 80 gives you a low end of 8k, and a high end of 80 if needed.

We are hitting 6 times below design temps in my region this week. Sometimes I think this is a better approach with unpredictable design day temps. At least you have the extra horsepower if you ever need it,

EBEBRATT-Ed

Sounds like your heat loss is accurate. I would go with a 50 gallon indirect. Boiler should at least cover your heat loss. Size heat emitters based on the water temp you want to run, must be below boilers maximum temperature. The lower the better to increase the efficiency

Sounds like your Viessman guy knows what he is doing

TAG

Radiant heat. Other sizes were recommended -- but do I really want to put in a 100k boiler and be 40% oversized ... or 125k? Originally, I was concerned only about the hot water with the 67k. I get that they modulate ...

Here is the building: Heated slab on the lowest level -- most of the building has Warmboard sub-flooring. The uppermost level (living room) will have plates. One of the bathrooms is on the heated slab portion the rest of the building will be wood floors -- except a small part of the second bathroom.

This is an 30 x 48 old stone sanctuary with a new 18x25 2x6 addition (kitchen w/ basement). It's a church -- so it's multi level floors. All the floors are open to each other including the addition. The total SF is actually 2604sf for the stone part (37060 BTU) and 972sf (15785BTU) for the addition. Actually 3576sf Total. With a room to room heat load done of 52845 BTU. All with +4" of closed cell foam -- new windows.

I can only assume that the heat load is correct -- the cooling load is 34100 and 8745. For the AC -- I'm going to do a ducted system in the stone building and mini splits in the kitchen addition (no space for ducts). They will both be heat pumps as well. The 34100 makes that unit a 4T -- multi speed of some manufacturer.

Gordy

But Is there zoning? You have to think about that.

Especially above design conditions with a small load. The 53k is at design day.

Viessmann is a fine boiler, and that installer has a good grasp of the loads as you mentioned.

TAG

Gordy -- Small load? Are you taking warm day? The design temp on the wrightsoft says 10 degrees .. we do get some days colder ... but it's uncommon. I was told there was some factoring in that figure within the software -- I don't know how much. So I don't know what occurs on a 5 degree day when I want 72. With a 10 - 70 design ... even at 95% efficiency the boiler should give 63k -- that's 8k above the heat load needed at 10 degrees.

These are the things I don't understand. With my CI Buderus using the Eccomatic -- it just modulates based on outdoor temp into my panel and floor radiant. But it's a 119k -- 85% feeding a 40g Buderus indirect. Being high mass it does not cycle all that often.

I was able to layout the Warmboard so each room/ area can be zoned. It was surprising how the loop lengths worked out. Only the bathroom zone is a bit short in length. In reality, I'm not sure how important it will be. Most of the house is so open. But, it's easy to place a valve controller on any loop of the manifold -- I'm going to burry some wires just in case. The lower level slab will be one zone .. my thought was to see how it works with two temp outdoor reset .. and modify from there.

I was also debating on maybe a heated towel rack ....

bob eck

If you do not want to go high efficiency condensing LP gas boiler or combi boiler you could look at using a Weil Mclain GV90 LP gas boiler and a indirect water heater.
The Weil Mclain GV90 is 90% AFUE and this boiler can be sidewall vented with PVC and I believe with CPVC SCH80 and polypropylene vent pipe. Check their installation book for approved vent pipe.
You can get a condensing boiler and use a indirect water heater with a coil and use that during the heating season and have electric elements in the indirect water heater and use it as a electric water heater during the non heating season. Plus if the boiler goes down and it takes a few days to get parts you can still have domestic hot water using the electric elements.

TAG

I see something about an EDR .. radiation. Not sure what that is.

TAG

Bob -- The mechanical room is small -- so I'm limited. Viessmann also makes the 22 w/ the tank. Not something anyone has used around me and the smaller size (they make two it looks like) matches the 67k boiler output -- but I think it may only have 32 gallons .... so now I'm back to the hot water worry.

I'm going to be venting through the roof and intake through the side wall.

sunlight33

Once I limited my Viessmann to 50% max. output, since it's a 114k boiler, half would be 57k. I was monitoring the DWH temp when my wife was taking a shower, and it's below 90 degrees when she finished, so definitely not good when two people shower at the same time. She likes it hot btw.

Gordy

What I’m driving at is IF you are zoning the zones calling individually can cause short cycling. Especially when it is warmer than design day.

It’s an open floor plan, and it sounds like you are not zoning which is good.

TAG

Sunlight33. On my two first Buderus boilers back in the early 90's - did a ST151 indirect -- it looks like a blue diving bell with three legs. Thermoglase coated steel tank and coil -- it's unbelievably heavy. My memory is they are under 40g. When they were first installed the boiler would would not hit 180 limit before they were satisfied. As they aged the boiler would hit the limit -- also had to bump up the temp. The first one failed about a year ago -- so 25+ years .. I replaced it with the 40g Buderus all SS model. The current thermoglase are of a different design and don't get great reviews. This new tank has to be set higher to satisfy the shower load in the morning -- it's just does not transfer as well (maybe less coils) I also think the mass of the old tank was so great that it held more heat so the incoming cold water was tempered a bit. The SS Viessmann tank gives me some concern as it's the same design as the Buderus.

sunlight33

I have a 53-gal Viessman indirect, with 75-80% max. output from the boiler, it can provide hot water to two showers endlessly.

hot_rod

Sounds like a 40 gallon indirect has always served your needs, go with that, top size if you plan on filling a large tub, perhaps.

Any of the small modulation boilers you mentioned are fine, Sounds like the Viessmann bid did his homework with the load calc. That in itself indicates he is a professional.

You may be able to run all systems on one temperature with some planning, or one high and mixed.

After the load calc would be design to spell out temperatures and flow rates requires in the various zones and emitters.

Contractors may not supply the design specs, with their bid, as some HOs will shop around a free design